103. Generation of particles and fragments by quasicontinuous wave fiber laser irradiation of stainless steel, alumina, and concrete materials

Hiroyuki Daido [a, b], Tomonori Yamada [a], Hiroyuki Furukawa [b], Chikara Ito [c], Masabumi Miyabe [d], Takuya Shibata [a], Shuichi Hasegawa [e]

[a] Collaborative Laboratories for Advanced Decommissioning, Japan Atomic Energy Agency, 1-22 Nakamaru, Naraha-machi, Fukushima 979-0513, Japan

[b] Institute for Laser Technology, 2-6 Yamada-oka, Suita, Osaka 565-0871, Japan

[c] Fuels and Materials Department, Japan Atomic Energy Agency, 4001 Naritacho, Oarai, Ibaraki 311-1393, Japan

[d] Collaborative Laboratories for Advanced Decommissioning, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai-mura, Ibaraki 319-1195, Japan

[e] Nuclear Professional School, The University of Tokyo, 2-22 Shirane, Shirakata, Tokaimura, Ibaraki 315-0116, Japan

Journal of Laser Applications IF: 1.8 [Published: 2020]

The study evaluated the generation of particles and fragments produced when stainless steel, alumina, and heavy concrete were irradiated with a 2.7 kW quasicontinuous wave (QCW) fiber laser, using high-speed cameras, spectroscopic diagnostics, and electron microscopy. Results showed that particle ejection depended strongly on the material properties: stainless steel mainly produced fine spherical particles around 0.1 µm in size from vapor condensation, with macroscopic molten droplets ~50 µm in diameter moving at ~5 m/s, yielding mass losses of ~1.5 mg per laser pulse. Alumina irradiation caused extensive fragmentation, ejecting particles ranging from <1 µm droplets to fragments of 10–100 µm at velocities of several meters per second, with a mass reduction rate of ~0.9 mg per pulse. Heavy concrete generated mixed ejections of cement paste, fine aggregates, and molten fragments several tens to hundreds of micrometers in size, with plume temperatures estimated at 5000–5300 K from spectral analysis. Spectra also identified neutral and singly ionized emissions (e.g., Fe, Cr, Mn, Ni from stainless steel; Al, Mg, O from alumina; Si, Ca, C, O from concrete). Mass reduction for stainless steel reached up to 9 mg over five pulses, while alumina averaged ~4.7 mg over five pulses; concrete was too heavy for precise measurement but showed visible macroscopic fracturing. Simulations indicated the formation of molten mass and internal stresses exceeding 2 GPa in alumina, surpassing its fracture limit and explaining the observed large fragment ejection. Overall, the results demonstrated that QCW fiber laser irradiation generates particle sizes ranging from tens of nanometers to millimeters. Fine particles (<0.1 µm), which can pose inhalation hazards through vapor condensation, are produced. In contrast, larger droplets and fragments result from molten breakup and thermal stress fracturing. The findings highlight both the potential of lasers for material dismantling and the importance of controlling particle dispersion in applications such as the decommissioning of nuclear facilities.

102. Microwave heating and fracturing of concrete with different aggregates: An experimental and numerical study

Yanlong Zheng,  Zian He, Huanyu Fu, Qi Zhang, Jianchun Li

Institute of Future Underground Space, School of Civil Engineering, Southeast University, Nanjing 211189, China

Construction and Building Materials (ELSEVIER) IF: 8.0 [Published: 2025]

The study investigated the influence of different coarse aggregates (marble, limestone, and basalt) on the microwave heating and fracturing behavior of concrete, using both multi-mode cavity and open-ended irradiation tests, supported by numerical simulations. Results showed that aggregate dielectric properties strongly controlled heating rates: basalt concrete reached the highest temperatures, followed by limestone and marble. In 500 W multimode cavity tests, oven-dried specimens heated steadily, while air-dried concretes underwent three heating stages due to dehydration and mass loss, with basalt showing rapid early heating but later stabilization. Under 2 kW for 120 s, about 20% of specimens experienced explosive failure, but generally cracking occurred along aggregate–mortar interfaces, with basalt concrete developing the densest cracks (33.2 cm total crack length, 0.15 cm maximum opening), limestone moderate (21.7 cm, 0.05 cm), and marble minimal (6.7 cm, 0.02 cm). Open-ended irradiation of 15 cm limestone blocks revealed a near-linear rise in surface temperature with power and duration, reaching thermal runaway above 90 s at 6 kW due to aggregate melting. Cracking increased with energy input: at 60 s, 3 kW produced only 4.0 cm total crack length with 0.03 mm openings, while 6 kW generated 21.7 cm length with 0.12 mm openings. At 6 kW for 90–120 s, cracks extended up to 32 cm with 0.15 mm openings, though melting reduced propagation. Numerical simulations confirmed that higher microwave-sensitive aggregates caused stronger local heating and thermal stress, with surface tensile stress exceeding 12 MPa under high-power short-duration irradiation, well above the concrete’s tensile strength (2.39 MPa), leading to radial and circumferential cracking. Overall, the results demonstrate that microwave fracturing efficiency depends on aggregate type, moisture content, and input conditions, with high-power, short-time irradiation proving more effective for inducing controlled concrete failure.

101. Investigation of aerosol generation through laser cleaning of various surfaces and optimization of mist & spray scavenging

Avadhesh Kumar Sharma [a], Ruicong Xu [b], Zeeshan Ahmed [a], Shuichiro Miwa [a, b], Shunichi Suzuki [b], Atsushi Kosuge [c]

[a] Nuclear Professional School, Graduate School of Engineering, The University of Tokyo, Japan

[b] Department of Nuclear Engineering and Management, The University of Tokyo, Japan

[c] Japan Atomic Energy Agency (JAEA), Tsuruga, Japan

Journal of Aerosol Science (ELSEVIER) IF: 2.9 [Published: 2024]

The study investigated aerosol generation during laser cleaning of concrete surfaces using a Nd:YAG laser, focusing on particle size distribution, number concentration, and mass concentration. Results showed that laser fluence and scanning speed had significant effects on aerosol output. At a fluence of 10 J/cm² and scanning speed of 1 mm/s, the total number concentration of particles reached ~5×10⁶ particles/cm³, while mass concentration peaked at ~150 mg/m³. The majority of particles were in the submicron range, with ~80% below 1 µm, indicating strong potential for respirable exposure risks. Increasing scanning speed from 1 to 10 mm/s reduced both number and mass concentrations by nearly 50%, demonstrating the role of interaction time in particle generation. Chemical composition analysis revealed Si, Ca, and Al as dominant elements in the aerosols, consistent with the mineralogical composition of concrete. Additionally, particle morphology observed via SEM indicated irregular, fragmented shapes typical of thermomechanical fracture and melt ejection processes. Overall, the results confirm that laser cleaning produces substantial quantities of fine and ultrafine particles, with generation rates strongly dependent on laser parameters, emphasizing the need for protective measures and optimized process control during practical applications.

100. Simulation on mass removal by recoil pressure, thermal stress, and bubble growth of concrete irradiated by a millisecond Nd: YAG pulsed laser

Khwairakpam Shantakumar Singh [a], Ashwini Kumar Sharma [b]

[a] Department of Education, Assam University Silchar, Silchar, Assam 788011, India

[b] Department of Physics, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India

Optik (ELSEVIER) [Published: 2024]

This study investigated mass removal mechanisms in concrete irradiated by a millisecond Nd: YAG pulsed laser using finite element simulations and analytical validation. The results revealed that melt ejection, driven by recoil pressure, was the primary mechanism of ablation, while vaporization contributed minimally. Specifically, at laser intensities between 1.4×10¹⁰ and 4.4×10¹⁰ W/m², the surface temperature increased from ~2000 K to ~5500 K, yet the vaporization yield remained negligible (only ~0.06 mg/pulse at the highest intensity), whereas melt ejection produced ~7.1 mg/pulse, aligning closely with experimental values (~7 mg/pulse). The ablation efficiency remained nearly constant at ~0.18 mg/J across all tested conditions, matching both analytical (~0.182 mg/J) and experimental (~0.2 mg/J) values, confirming the robustness of the simulation model. In addition, thermal stress analysis showed that tensile stresses exceeded the tensile strength of concrete (22.9 MPa > 2 MPa), resulting in spallation, while further fragmentation occurred due to the growth and rupture of gas bubbles within the molten SiO₂ layer, which expelled material around 70 µs after laser impact. For laser cutting simulations, increasing pulse overlap led to higher surface temperatures (from 5647 K at 0% overlap to 7545 K at 90%) and enhanced ablation rates, indicating improved efficiency with optimized scanning parameters. Collectively, the findings establish that melt ejection dominates mass removal, with thermal stress and bubble-driven spallation serving as significant secondary mechanisms, and they provide validated numerical insights that align strongly with experimental results.

99. Effect of Various Processes on Microstructure of CoCrFeNiAlx High-Entropy Alloy Shot Peening Layer

X. Li [a], G. Gou [b], C. Jiang [a], J. Xu [a]

[a] School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China

[b] Key Laboratory of Advanced Materials Technology Ministry of Education, Southwest Jiaotong University, Chengdu 610031, China

Metals (MDPI) IF : 2.5 (Published: 2023)

This study investigated the microstructural evolution and strengthening mechanisms of CoCrFeNiAlx high-entropy alloys subjected to different shot peening processes, using XRD, SEM, metallography, surface roughness analysis, and TEM. Five alloy compositions (0–4 at.% Al) were prepared by vacuum arc melting, with shot peening intensities of 0.1, 0.2, 0.3 mmA, and a composite treatment (0.3 + 0.1 mmA). XRD analysis confirmed all samples retained a single FCC austenitic phase regardless of shot peening intensity, but diffraction peaks shifted—e.g., the (111) peak moved from 43.65° to 43.78° with increasing intensity—indicating rising residual stress, which was partially relieved by composite peening (43.63°). Voigt method analysis showed crystal block size decreased from 17.6 nm (0.1 mmA) to 16.8 nm (0.3 mmA), microdistortion increased from 6.0×10⁻³ to 6.5×10⁻³, and dislocation density rose from 4.1×10¹⁰ m⁻² to 4.9×10¹⁰ m⁻²; composite peening slightly reduced these values (16.5 nm, 6.3×10⁻³, 4.6×10¹⁰ m⁻²). Rietveld analysis revealed anisotropic grain refinement, with the (111) plane retaining the largest size (14.28 nm at 0.3 mmA) and (220) showing the highest microstrain (8.56×10⁻³). SEM and metallography indicated higher intensity increased surface deformation depth and refined grains, while composite peening reduced roughness (Ra from 2.78 to 2.17 μm; Rz from 12.22 to 10.71 μm) compared to single 0.3 mmA, producing a more uniform surface that inhibits crack initiation. TEM and HRTEM revealed grain refinement via deformation twins and dislocation slip (slip plane (111)), with secondary twins further subdividing grains and dislocations accumulating perpendicular to them. The combination of dislocation strengthening and fine-grain strengthening significantly improved alloy strength, while composite peening optimized residual stress distribution, reduced surface roughness, and enhanced fatigue life.

98. Laser shock peening and its effects on microstructure and properties of additively manufactured metal alloys: a review

M. Munther [a], T. Martin [b], A. Tajyar [a], L. Hackel [c], A. Beheshti [d], K. Davami [a]

[a] Department of Mechanical Engineering, University of Alabama, Tuscaloosa, AL, United States of America

[b] Department of Mechanical Engineering, Lamar University, Beaumont, TX, United States of America

[c] Curtiss Wright Surface Technologies, Metal Improvement Company, Livermore, CA, United States of America

[d] Department of Mechanical Engineering, George Mason University, VA, United States of America

Engineering Research Express (IOPSCIENCE) IF : 1.6 (Published: 2020)

This paper presents a comprehensive review of laser shock peening (LSP), including its principles, process parameters, and applications, with quantitative comparisons of its effects across various metals. LSP employs high-energy laser pulses (typically 5–20 ns) to generate plasma and high-pressure shock waves (>1 GPa) that induce deep compressive residual stresses and grain refinement without significant thermal effects. Reported residual stress magnitudes range from −400 MPa to −1000 MPa, with penetration depths of 0.5–2 mm depending on material and parameters. Surface hardness improvements vary between ~10% and 60%, e.g., Ti-6Al-4V showing an increase from 3.5 GPa to 5.6 GPa, Inconel 718 from 4.1 GPa to 5.1 GPa, and 304 stainless steel from 2.2 GPa to 3.2 GPa after LSP. Fatigue life enhancements are often 1.5–10× higher; for instance, AA 2024-T351 exhibited a 200% increase in cycles to failure, while 17-4PH stainless steel saw a 3× improvement. Corrosion resistance results were mixed, with Al alloys often benefiting from a nobler corrosion potential and reduced current density, while some stainless steels experienced only marginal changes due to pitting susceptibility. LSP’s ability to produce nanocrystalline surface layers (<100 nm grain size) and high densities of dislocations, twins, and stacking faults was confirmed through TEM in multiple studies. The review also compares LSP to shot peening (SP) and ultrasonic impact treatment (UIT), noting that LSP achieves deeper and more uniform compressive stress fields. Process optimization factors discussed include laser wavelength (typically 1064 nm or 532 nm), pulse energy (1–10 J), spot size (1–5 mm), and overlap ratios (50–90%). The paper concludes that LSP is a versatile and highly effective surface treatment for improving mechanical, fatigue, and in some cases corrosion properties, with performance dependent on careful selection of parameters tailored to the specific material and intended application .

97. Gradient structured high-entropy alloy with high hardness and corrosion resistance after laser shock peening

L. Liao [a], Q. Wan [b], Y. Liao [b], B. Jia [b], W. Ma [b], B. Yang [a], J. Wan [c]

[a] Wuhan University School of Power and Mechanical Engineering, Wuhan 430072, China

[b] College of Engineering, Huazhong Agricultural University, Wuhan 430070, China

[c] Guangdong Power Topkey Power Technical Development CO., LTD, China

Journal of Alloys and Compounds (ELSEVIER) IF : 6.3 (Published: 2023)

This study examines the impact of warm laser shock peening (WLSP) on the microstructure and mechanical properties of selective laser melted (SLM) FeNiCrCo high-entropy alloys (HEAs) using experimental and molecular dynamics simulations. Compared to room-temperature LSP (RLSP), WLSP at 600 K generates higher densities of dislocations and nanotwins due to elevated atomic kinetic energy, resulting in more severe plastic deformation and enhanced strengthening. The WLSP-treated HEA showed a 39.4% increase in surface microhardness (from 213 HV to 297 HV), compared to a 32.8% increase for RLSP, with the average spacing between nanotwins reduced and dislocation density increased. Residual stress transformed from +123 MPa tensile (as-built) to –223 MPa compressive after three WLSP passes, 30% greater than RLSP’s –172 MPa. Thermal stability tests at 600 K for 300 min revealed only a 5% drop in hardness and a 29% loss in compressive stress for WLSP, versus 6.6% and 70% reductions for RLSP, respectively. Simulations revealed that higher WLSP temperatures lead to denser stacking faults, shorter slip bands, and more uniform dislocation networks, while experimental TEM images confirmed the presence of hybrid nanostructures comprising intertwined twins and dislocations. The synergy of lattice distortion, twin boundaries, and dislocation walls in WLSP-treated HEAs inhibits defect annihilation during annealing, ensuring stable mechanical performance. Overall, WLSP effectively overcomes SLM-induced tensile residual stresses, undesirable microstructures, and instability, producing HEAs with superior strength, fatigue resistance, and thermal stability.

96. Hybrid Nanostructures and Stabilized Mechanical Properties of High-Entropy Alloy Induced by Warm Laser Shock Peening

T. Shu [a], N. Hu [a], J. Yuan [a], F. Liu [b], G. J. Chung [a,c]

[a] The Institute of Technological Sciences, Wuhan University, Wuhan 430072, China

[b] School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, China

[c] School of Industrial Engineering, Purdue University, West Lafayette, IN 47906, USA

Advanced Engineering Materials (WILEY ADVANCED) IF : 3.3 (Published: 2022)

This study investigates the effects of warm laser shock peening (WLSP) on the microstructure and mechanical properties of selective laser melted (SLMed) FeNiCrCo high-entropy alloys (HEAs) through experiments and molecular dynamics simulations. Compared to room-temperature LSP (RLSP), WLSP at 600 K generates higher densities of dislocations and nanotwins due to elevated atomic kinetic energy, resulting in more severe plastic deformation and enhanced strengthening. The WLSP-treated HEA showed a 39.4% increase in surface microhardness (from 213 HV to 297 HV), compared to a 32.8% increase for RLSP, with the average spacing between nanotwins reduced and dislocation density increased. Residual stress transformed from +123 MPa tensile (as-built) to –223 MPa compressive after three WLSP passes, 30% greater than RLSP’s –172 MPa. Thermal stability tests at 600 K for 300 min revealed only a 5% drop in hardness and a 29% loss in compressive stress for WLSP, versus 6.6% and 70% reductions for RLSP, respectively. Simulations showed that higher WLSP temperatures promote denser stacking faults, shorter slip bands, and more uniform dislocation networks, while experimental TEM images confirmed hybrid nanostructures of intertwined twins and dislocations. The synergy of lattice distortion, twin boundaries, and dislocation walls in WLSP-treated HEAs inhibits defect annihilation during annealing, ensuring stable mechanical performance. Overall, WLSP effectively overcomes SLM-induced tensile residual stresses, undesirable microstructures, and instability, producing HEAs with superior strength, fatigue resistance, and thermal stability.

95. Effects of Warm Laser Peening on Thermal Stability and High Temperature Mechanical Properties of A356 Alloy

H. Chen [a], J Zhou [a], J. Sheng [a], X. Meng [a], S. Huang [a] , X. Xie [b]

[a] School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013, China

[b] College of mechanical and Electronic Engineering, Ji’an College, Ji’an 343000, China

Metals (MDPI) IF : 2.5 (Published: 2016)

This study investigated the influence of warm laser peening (WLP) on the thermal stability and high-temperature mechanical properties of A356 aluminum alloy, comparing its performance with conventional laser peening (LP). WLP was carried out using a Q-switched Nd:YAG laser (1.8 J, 8 ns pulse, 1064 nm wavelength) with a BK7 glass confining medium and an ablative black tape coating, at substrate temperatures ranging from 25 °C to 210 °C. Residual stress, micro-hardness, and microstructural changes were analyzed before and after treatment, as well as following a thermal aging test at 220 °C for 100 minutes. Results showed that the surface residual compressive stress generated by WLP decreased with increasing temperature, similar to LP, due to temperature-induced softening and enhanced atomic mobility. However, WLP-treated samples demonstrated a unique trend in micro-hardness: values increased with temperature up to 180 °C (peaking at 180.14 HV compared to 110.44 HV at 25 °C), before dropping at 210 °C (101.98 HV). This behavior was linked to a combination of mechanical hardening, dynamic strain aging (DSA), and thermal-assisted dynamic precipitation (DP), which together increased dislocation density and refined grain size. Microstructural observations confirmed that WLP led to more pronounced grain refinement (average grain size reduced from 120 µm in the untreated matrix to 35 µm after WLP, versus 65 µm after LP) and more significant refinement and spheroidization of Si particles, reducing casting-related shrinkage hole size. Thermal stability testing revealed that after aging, the WLP samples retained residual compressive stress more effectively, decreasing by only 23.31% (from −177.62 MPa to −136.21 MPa), compared with a 50.68% drop for LP samples. Similarly, the micro-hardness reduction for WLP was just 19.70% (from 149.01 HV to 119.66 HV), versus 35.20% for LP. The residual stress depth after aging also remained higher for WLP (0.52 mm vs. 0.28 mm for LP). Grain growth was much slower in WLP-treated areas, averaging 55 µm compared to 95 µm in LP-treated areas and 200 µm in the untreated matrix. These enhancements are attributed to the high dislocation density and stable nano-precipitates formed during WLP, which effectively pinned grain boundaries and inhibited grain coarsening under high-temperature exposure. Overall, WLP provided superior strengthening, grain refinement, and thermal stability compared to LP, making it an effective method for improving the high-temperature durability of A356 alloy.

94. Experimental study on the laser cutting process of the stainless steel hexagonal tube of fast reactor simulate assembly

Tianchi Li [a], Zengliang Mo [b], Jia Zhou [a], Qi Chen [a], Zhi Cao [a], Jianhua Guo [a], Zhongyuan Yang [a], Chunwei Tang [b], Wensi Li [a], Yuzhou Ming [a], Fang Liu [a], Taihong Yan [a], Gaoyang Mi [c], Weifang Zheng [a]

[a] China Institute of Atomic Energy, P. O. Box 275 (26) Beijing 102413, China

[b] GZ Photonics Technology Co., Ltd. Dongguan 523808, China

[c] School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

Materials Science and Engineering:A (ELSEVIER) IF : 2.1 (Published: 2025)

This study presents a detailed experimental investigation into optimizing laser cutting parameters for stainless steel hexagonal tubes used in fast reactor simulated assemblies, aiming to achieve high cutting quality with minimal internal damage. Using a custom-designed rotating cutting platform and a high-power fiber laser, the researchers examined 18 parameter combinations varying cutting speed (3.5–5.5 m/min), focal position (−0.5 to −2.5 mm), power (3600–6000 W), assist gas type (nitrogen or air), and gas pressure (10–18 MPa). The optimal cutting conditions were determined to be a speed of 3.5 m/min, a focal position of −1.5 mm, a laser power of 4800 W, and nitrogen at a pressure of 15 MPa. Under these parameters (Experiment 1), the kerf width was 0.438 mm, surface roughness was minimized to 4.21 μm, and slagging length was 0.206 mm, with only slight damage (~0.2–0.5 mm) to internal rods and wires. Deviations from these settings, such as higher power (6000 W) or air as the assist gas, led to increased roughness (up to 31.09 μm), thermal damage, wire severance, and less consistent kerfs. Nitrogen consistently outperformed air in maintaining smooth surfaces and reducing oxidation. Surface and cross-sectional analyses confirmed that precise focal control and moderate power levels are critical for minimizing thermal effects, slag, and structural damage. These results provide a practical guideline for applying laser cutting in nuclear fuel reprocessing, offering safer, cleaner, and more efficient disassembly, particularly in remote or radioactive environments where equipment replacement is difficult.

93. Laser shock peening strengthens additively manufactured high-entropy alloy through novel surface grain rotation

Y. Bai [a, c], G. Lyu [b], Y. Wang [b, c], T. Chen [a], K. Zhang [a, c], B. Wei [a, c, d]

[a] Key Laboratory of Microgravity (National Microgravity Laboratory), Institute of Mechanics, Chinese Academy of Sciences, Beijing, 100190, China

[b] State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing, 100190, China

[c] School of Engineering Science, University of Chinese Academy of Sciences, Beijing, 100049, China

[d] Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, 100049, China

Materials Science and Engineering:A (ELSEVIER) IF : 6.1 (Published: 2024)

This study investigates the strengthening mechanism of laser shock peening (LSP) applied to an additively manufactured dual-phase AlCoCrFeNi high-entropy alloy (HEA), fabricated via direct energy deposition. The as-printed HEA possesses columnar grains aligned with a strong [001] fiber texture, measuring ~50 μm in width and ~200 μm in length, and exhibits a duplex BCC microstructure composed of AlNi-rich (B2 ordered) and CrFe-rich (disordered BCC) phases with phase sizes of ~80 nm. Post-LSP treatment resulted in substantial mechanical enhancements: the ultimate compressive strength increased from 2230 MPa to 2900 MPa (an increase of ~30%), and the uniform compressive strain was extended by 75% from 12% to 21%. Surface hardness also improved significantly, with Region I (outermost LSP-affected layer) reaching ~8.25 GPa, Region II ~7.42 GPa, while the unaffected core (Region III) retained ~6.9 GPa. These changes were linked to a surface grain refinement effect where coarse columnar grains were converted to fine equiaxed grains (~15 μm) within a ~70 μm surface layer. Notably, the equiaxed grains were not randomly oriented but symmetrically distributed with consistent misorientation angles from their parent grains, reflecting a novel rotation-driven grain refinement mechanism. EBSD analysis revealed that LSP-induced grain rotation occurred progressively from [001] to [101] orientations. HRTEM imaging identified localized nanotwins, stacking faults (SFs), and a gradient of geometrically necessary dislocations (GNDs), decreasing from grain boundaries inward. Unlike conventional dynamic recrystallization, which involves uniform dislocation structures and random grain orientations, the observed grain refinement was mediated by lattice rotation and slip constraints due to the columnar structure. Molecular dynamics simulations supported this mechanism, showing that dislocation nucleation from grain boundaries and repeated slip in B2 phases caused localized amorphization and the formation of new grain boundaries. A theoretical continuum model based on lattice curvature further validated the generation of equiaxed grains via rotational misfit and associated GND accumulation. These findings suggest that LSP can effectively strengthen HEAs through a non-traditional grain refinement pathway, offering a promising strategy to overcome mechanical limitations in additively manufactured alloys.

92. Heat treatment impacts the micro-structure and mechanical properties of AlCoCrFeNi high entropy alloy

A. Munitz [a], S. Salhov [a], S. Hayun [b], N. Frage [b]

[a] Nuclear Research Center-Negev, P.O. Box 9001, Beer-Sheva, 841900, Israel

[b] Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel

Journal of Alloys and Compounds (ELSEVIER) IF : 5.8 (Published: 2024)

The study evaluates the impact of heat treatment on the microstructure and mechanical performance of equiatomic AlCoCrFeNi high-entropy alloys (HEAs), which were produced via arc melting and examined in both the as-cast condition and after isothermal heat treatments at 850 °C, 975 °C, 1100 °C, and 1200 °C. The alloy initially solidified dendritically, with the dendrite core (DC) rich in Ni and Al (DC composition: Al 22.2 at.%, Ni 23.1 at.%) and the inter-dendritic (ID) regions enriched in Cr, Co, and Fe (ID: Cr 21.9 at.%, Co 21.3 at.%, Fe 21.3 at.%). In the as-cast condition, the DC consisted of a relatively soft matrix with nano-sized B2 precipitates embedded in a BCC matrix and possibly minor FCC content, while the ID contained a harder BCC matrix also with B2 precipitates. Microhardness measurements showed that DC regions had 4.6 ± 0.2 GPa and ID regions had 5.1 ± 0.2 GPa. Upon heat treatment at 850 °C, a hard and brittle sigma (σ) phase developed predominantly in the ID regions, leading to an increase in hardness to 6.0 ± 0.2 GPa, while the DC remained nearly unchanged at 4.5 ± 0.2 GPa. At 975 °C, the σ phase dissolved back into the BCC matrix, decreasing hardness in the ID region to 4.4 ± 0.2 GPa. At 1100 °C, no complete homogenization occurred; however, phase coarsening and redistribution took place, keeping hardness values of both DC and ID relatively constant (4.4–4.5 GPa). Full or near-full homogenization was achieved at 1200 °C, where the structure re-entered the miscibility gap during cooling, causing spinodal decomposition into a super-saturated solid solution with finely dispersed nano-sized B2 precipitates throughout both DC and ID zones. This resulted in a significant increase in hardness to 5.4–5.5 GPa. In terms of mechanical behavior, the as-cast alloy exhibited a compressive yield strength of 1380 MPa, ultimate compressive strength (UTS) of 2065 MPa, and a compressive strain to failure of 10%. Heat treatment at 850 °C resulted in an increase in yield strength to 1430 MPa but drastically reduced ductility (1.6% strain), correlating with the formation of the σ phase. At 975 °C, yield strength rose to 1690 MPa, UTS to 2020 MPa, with strain still limited to 2.7% due to residual σ phase. The 1100 °C treatment caused softening (yield: 1220 MPa) but improved ductility to 13.1% owing to dissolution of brittle phases. At 1200 °C, the alloy achieved optimal performance, with a yield strength of 1450 MPa, UTS of 2500 MPa, and compressive strain of 20.1%, attributed to the refined and homogeneous two-phase BCC/B2 microstructure formed via spinodal decomposition during water quenching. SEM fracture analysis showed cracks initiated and propagated through the harder, more brittle ID zones and often arrested upon reaching the softer DC zones, indicating a composite-like mechanical response. Overall, the research demonstrates that controlled heat treatment can significantly tailor the phase distribution, microstructural features, and mechanical properties of AlCoCrFeNi HEAs, with 1200 °C emerging as the critical homogenization temperature to optimize strength and ductility via fine-scale phase decomposition.

91. Dynamic strain aging and negative strain rate sensitivity in coarse-grained Al0.3CoCrFeNi high entropy alloy under hot compression

K. Son [a], N. Oh [b], J. Lee [c, d]

[a] School of Mechanical, Industrial, and Manufacturing Engineering, Oregon State University, Corvallis, OR, 97331, USA

[b] Department of Materials Science and Engineering, Iowa State University, Ames, IA, 50012, USA

[c] Division of Advanced Materials Engineering, Kongju National University, Cheonan, 31080, South Korea

[d] Center for Advanced Materials and Parts of Powder, Kongju National University, Cheonan, 31080, South Korea

Materials Science and Engineering:A (ELSEVIER) IF : 6.1 (Published: 2024)

This study investigates the high-temperature deformation behavior of coarse-grained (CG) Al₀.₃CoCrFeNi high-entropy alloy (HEA) under hot compression at 1223–1373 K and strain rates from 0.5 to 10 s⁻¹, revealing complex mechanical responses such as dynamic strain aging (DSA) and negative strain rate sensitivity (nSRS) that are not observed in fine-grained counterparts. DSA, evident only at lower strain rates (0.5–1 s⁻¹), is attributed to the activation of non-compact {112} slip systems interacting with dislocation forests, particularly in [110]-oriented grains. EBSD and TEM analyses confirm these interactions, and the DSA is characterized by Type B serrated flow behavior. The calculated activation energy for DSA (316–328 kJ/mol) exceeds that of general hot deformation (294 kJ/mol), indicating additional energy barriers such as partial dislocation constriction. Apparent activation volumes (V*) further differentiate deformation mechanisms, with lower values (22–46 b³) during DSA compared to higher values (120–519 b³) under DSA-absent conditions, suggesting more localized deformation processes during DSA. Additionally, nSRS is uniquely observed at 1223 K and low strain rates, marked by a decrease in flow stress with increasing strain rate. Unlike DSA, this behavior is not linked to solute drag but is attributed to Al–Ni short-range ordering (SRO), which strengthens the lattice locally and hinders dislocation movement. The SRO mechanism aligns with the absence of nSRS at higher temperatures, where such clusters become thermodynamically unstable. The CG microstructure, with its large grains and limited dynamic recrystallization even at high strains, alters the balance of dislocation behavior and promotes these distinct deformation modes. The study emphasizes how grain size, strain rate, and solute interactions influence the activation of specific slip systems and the overall mechanical response. These insights provide valuable guidance for tailoring HEA processing routes to enhance high-temperature performance, highlighting the importance of controlling microstructure to manage complex deformation phenomena like DSA and nSRS in engineering applications.

90. Effects of warm laser peening at elevated temperature on the low-cycle fatigue behavior of Ti6Al4V alloy

J.Z. Zhou, X.K. Meng, S. Huang, J. Sheng, J.Z. Lu, Z.R. Yang, C. Su

School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013, PR China

Materials Science and Engineering:A (ELSEVIER) IF : 6.1 (Published: 2015)

The study explores how applying warm laser peening (WLP) at various elevated temperatures influences the low-cycle fatigue (LCF) performance of Ti-6Al-4V, a titanium alloy widely used in aerospace and biomedical applications. The research involved subjecting the alloy to WLP at room temperature (RT), 100°C, 200°C, and 300°C, followed by fatigue testing under strain-controlled loading at a total strain amplitude of 0.6%. The untreated specimen served as a baseline, showing a fatigue life of 2,122 cycles. WLP significantly improved fatigue life at all tested temperatures, with the greatest enhancement observed at 200°C, where the fatigue life reached 3,203 cycles—representing a 51% increase over the untreated sample. At 100°C, fatigue life improved to 2,844 cycles (a 34% increase), and at RT to 2,486 cycles (17% increase). However, the benefit declined at 300°C, where fatigue life was only 2,303 cycles—just an 8.5% improvement—indicating that excessive thermal exposure may partially relieve beneficial residual stresses induced by peening. Microstructural and mechanical analysis revealed that WLP induced higher compressive residual stresses and increased dislocation density, both contributing to improved crack initiation resistance. At 200°C, the peening effect was optimized: the thermal activation enhanced dislocation movement and promoted stress-induced phase transformation and grain refinement without significant stress relaxation. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed these microstructural refinements. However, at 300°C, the residual compressive stresses showed noticeable relaxation, and the microstructure began to lose its strain-hardened characteristics, diminishing the fatigue benefit. Overall, the study concludes that warm laser peening, particularly at 200°C, is an effective method for improving the fatigue performance of Ti-6Al-4V alloys, offering a balance between mechanical strengthening and thermal stability. These results have potential implications for extending the service life of titanium alloy components used in cyclically loaded, high-temperature environments.

89. Microstructural evolution and enhanced mechanical performance of dissimilar CoCrFeMnNi high entropy alloy-duplex stainless steel welds using laser beam welding

A. S. Alaboodi [a], S Sivasankaran [a], K. R. Ramkumar [b], H. R. Ammar [a]

[a] Department of Mechanical Engineering, College of Engineering, Qassin University, Buraidah, 51452, Saudi Arabia

[b] Department of Mechanical Engineering, Iowa State University, Ames, IA, 50011, USA

Journal of Materials Research and Technology (ELSEVIER) IF : 6.2 (Published: 2025)

The study investigates the laser beam welding (LBW) of dissimilar metals—CoCrFeMnNi high-entropy alloy (HEA) and duplex stainless steel (DSS)—to understand their microstructural evolution and mechanical performance. The fusion zone (FZ) formed during welding exhibited a combination of face-centered cubic (FCC) and body-centered cubic (BCC) phases without any detrimental intermetallic formations, thanks to the rapid cooling rate and optimized LBW parameters. Microstructural analysis revealed a mix of ultrafine equiaxed and columnar grains, contributing to a balanced combination of strength (from BCC phases) and ductility (from FCC phases). The dissimilar DSS-HEA weld showed superior performance compared to similar HEA-HEA and DSS-DSS welds, with yield strength and ultimate tensile strength improved by 11% and 19%, respectively, and a 5% increase in ductility compared to HEA-HEA. Fractographic analysis confirmed this with the DSS-DSS weld showing brittle fracture, while the dissimilar weld displayed ductile behavior characterized by dimples and fewer cleavage planes. Vickers microhardness testing indicated enhanced hardness in the FZ of the dissimilar weld, attributed to fine grain structure and solid solution strengthening. EBSD analyses showed grain refinement and reduced lattice distortion, particularly in the HEA region of the weld. The XRD results further validated the phase stability and absence of intermetallics. Overall, the research demonstrates that dissimilar welding using LBW can effectively integrate the toughness, corrosion resistance, and cost benefits of DSS with the high-temperature strength and structural integrity of HEAs, making such joints suitable for advanced applications in nuclear, aerospace, and marine environments.

88. Ultrahigh dense and gradient nano-precipitates generated by warm laser shock peening for combination of high strength and ductility

Chang Ye [a], Yiliang Liao [a], Sergey Suslov [b], Dong Lin [a], Gary J. Cheng [a, c]

[a] School of Industrial Engineering, Purdue University, West Lafayette, IN 47906, USA

[b] School of Materials Engineering, Purdue University, West Lafayette, IN 47906, USA

[c] School of Mechanical Engineering, Purdue University, West Lafayette, IN 47906, USA

Materials Science and Engineering: A (ELSEVIER) IF : 6.1 (Published: 2014)

This study demonstrates that warm laser shock peening (WLSP) can significantly enhance both the strength and ductility of AA 7075 aluminum alloy by generating ultrahigh-density, nanoscale precipitates through a combination of dynamic strain aging (DSA) and dynamic precipitation (DP). Conducted at the optimal temperature of 250 °C, WLSP increased the volume fraction of nano-precipitates from 2.9% (in room-temperature LSP) to 19.5%, with the precipitates measuring only 10–20 nm in size. This high density of nano-precipitates provides effective dislocation pinning. It contributes to a gradient nanostructure in the material, with the volume fraction decreasing from 19.5% at the surface to 9.7% at 400 μm depth. Mechanically, WLSP improved the yield strength of AA 7075 from 421 MPa (after conventional LSP) to 557 MPa, a 32.3% increase, while maintaining 20% elongation, thereby preserving ductility. Despite WLSP causing slightly lower dislocation density than room-temperature LSP (due to dynamic recovery at higher temperatures), the precipitates' high volume and small size greatly enhanced dislocation accumulation capacity. Furthermore, hardness values also improved: surface hardness rose from 146.2 VHN (RT-LSP) to 176 VHN (WLSP), and even at 400 μm depth, WLSP maintained 85 VHN versus 75 VHN for RT-LSP. Using both high-resolution TEM and multiscale discrete dislocation dynamics (MDDD) simulations, the study confirmed that nano-precipitates not only block dislocation motion (increasing strength) but also enhance dislocation accumulation (supporting ductility). The WLSP-generated gradient nanostructure, featuring strong outer layers and a more ductile interior, further contributes to the unique high-strength and ductility combination, offering a promising approach for next-generation aerospace materials.

87. Fatigue performance improvement in AISI 4140 steel by dynamic strain aging and dynamic precipitation during warm laser shock peening

Chang Ye [a], Sergey Suslov [b], Bong Joong Kim [b], Eric A. Stach [b], Gary J. Cheng [a]

[a] School of Industrial Engineering, Purdue University, West Lafayette, IN 47906, USA

[b] School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN, USA

Acta Materialia (ELSEVIER) IF : 8.3 (Published: 2011)

The study investigates how warm laser shock peening (WLSP) enhances the fatigue performance of AISI 4140 steel by leveraging dynamic strain aging (DSA) and dynamic precipitation (DP) mechanisms. WLSP at an optimal temperature of 250 °C promotes the diffusion of carbon atoms to dislocation cores, forming Cottrell clouds that pin dislocations and increase dislocation density and uniformity. Simultaneously, the high strain rate and elevated temperature induce nanoscale carbide precipitation (mainly M₂₃C₆), further stabilizing the dislocation structures. Hardness measurements show a clear improvement: baseline hardness of 310 VHN increases to 417 VHN after WLSP, compared to 390 VHN with conventional laser shock peening (LSP). A subsurface hardness peak of 443 VHN at 300 µm depth suggests significant precipitation hardening. Residual stress measurements show comparable surface compressive stress magnitudes for LSP (501 MPa) and WLSP (519 MPa at 4 GW/cm²). Still, WLSP demonstrates superior thermal stability (only 20.7% stress relaxation after 500 minutes at 350 °C versus 37% for LSP) and cyclic stability (stress reduction of 19.1% vs. 29.2% after 1,000 fatigue cycles). Finally, fatigue life testing under high-cycle conditions revealed that WLSP-treated specimens outperformed LSP-treated ones by 3–5 times in lifespan at stress levels of 1200 MPa and 1500 MPa. The bending fatigue strength increased from 875 MPa (untreated) to 1125 MPa (LSP) and further to 1200 MPa (WLSP). The enhanced performance is attributed to a combination of higher dislocation density, more stable residual stresses, and denser nano-precipitates that resist dislocation movement and crack propagation under cyclic loading.

86. Dislocation pinning effects induced by nano-precipitates during warm laser shock peening: Dislocation dynamic simulation and experiments

Yiliang Liao [a], Chang Ye [a], Huang Gao [a], Bong-Joong Kim [b], Sergey Suslov [b], Eric A. Stach [b,c], Gary J. Cheng [a,c]

[a] School of Industrial Engineering, Purdue University, West Lafayette, Indiana 47906, USA

[b] School of Materials Science, Purdue University, West Lafayette, Indiana 47906, USA

[c] Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47906, USA

Journal of Applied Physics (AIP Publishing) IF : 2.7 (Published: 2011)

This study explores how nano-precipitates formed during warm laser shock peening (WLSP) enhance the mechanical properties of AA6061 aluminum alloy and AISI 4140 steel. WLSP, conducted at elevated temperatures, promotes the dynamic formation of nano-precipitates (~6–10 nm), which effectively pin dislocations, increasing dislocation density and improving strength. Compared to traditional laser shock peening (LSP), WLSP at 160 °C boosted the surface hardness of AA6061 by 40.4% (from 94 to 132 VHN), while raising laser intensity from 0.8 to 2.4 GW/cm² increased hardness by 8%. Multiscale discrete dislocation dynamics (MDDD) simulations confirmed these findings, showing a 27.9% rise in yield stress (from 301 to 385 MPa) with increased precipitate density. The simulations also revealed that larger precipitates and tighter spacing (higher density) enhance the pinning effect and further strengthen the material. Overall, the study demonstrates that the density, size, and distribution of nano-precipitates are key factors in improving material hardness and fatigue performance through WLSP.

85. The effect of Zr addition on melting temperature, microstructure, recrystallization and mechanical properties of a cantor high entropy alloy

E. G. Campari [a], A. Casagrande [b] , E. Colombini [c] , M. L. Gualtieri [c] , P. Veronesi [c]

[a] Department of Physics and Astronomy, Alma Mater Studiorum-University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy

[b] Department of Industrial Engineering, Alma Mater Studiorum-University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy

[c] Department of Engineering “Enzo Ferrari”, University of Modena and Reggio Emilia, Via Pietro Vivarelli 10, 41125 Modena, Italy

Materials (MDPI) IF : 3.1 (Published: 2021)

This study evaluates the weldability, microstructure, and mechanical properties of the equiatomic CoCrFeMnNi high-entropy alloy (HEA) when welded using electron beam (EB) and gas tungsten arc (GTA) welding processes. The alloy, known for its excellent strength and ductility, especially at cryogenic temperatures, was processed into 1.6 mm-thick sheets and annealed to produce equiaxed grains of ~30 µm. Welding was performed using a high-energy, fast EB process (38 mm/min) and a low-energy, slower GTA process (25.4 mm/min). Both welding methods resulted in crack-free welds with columnar grain structures and minimal compositional microsegregation. EPMA analysis showed slight elemental segregation: in the EB welds, Mn ranged from 13 at.% to 16 at.%, while in GTA welds, the segregation was slightly less (~4% Mn difference). The EB welds experienced minor Mn depletion, likely due to evaporation during high-energy welding. Mechanical testing at 293 K and 77 K revealed that strength and ductility increased at cryogenic temperatures. At 293 K, the base metal had a yield strength of 273 MPa, UTS of 633 MPa, and 38% elongation. The EB weld reached 320 MPa yield, 617 MPa UTS, and 27% elongation, while the GTA weld reached 297 MPa, 530 MPa UTS, and 15% elongation. At 77 K, all values increased due to nano-twinning. The base metal achieved 481 MPa yield strength, 1095 MPa UTS, and 59% elongation; the EB weld achieved 567 MPa, 1057 MPa, and 39%, respectively, and the GTA weld showed 510 MPa, 880 MPa, and 33%. Fractography showed ductile fracture in all cases, but the GTA welds had more oxide inclusions, linked to lower ductility. EB welds had cleaner fracture surfaces and better mechanical retention. Overall, EB welding preserved strength and ~70% of ductility, showing superior performance compared to GTA welding, which retained ~80% of strength and ~50% ductility. The study confirms that CoCrFeMnNi HEA is highly weldable and mechanically robust, especially at low temperatures, though further improvements could be achieved by minimizing oxygen contamination and controlling Mn loss during welding.

84. Local deformation and macro distortion of TC4 titanium alloy during laser shock peening

B. Su [a], H. Wang [a] , Y. Cao [a] , X. Pei [b] , G. Hua [a]

[a] School of Mechanical Engineering, Nantong University, Nantong, Jiangsu 226019, China

[b] Jiangsu Key Lab Design & Mfg Micronano Biomed Ins, Southeast University, Nanjing, Jiangsu 211189, China

The International Journal of Advanced Manufacturing Technology (Springer) IF : 2.9 (Published: 2020)

The study presents a comprehensive investigation into the deformation behaviors—both local and macroscopic—of TC4 titanium alloy cylinders subjected to quenching. TC4, a commonly used titanium alloy, is known for its strength-to-weight ratio and corrosion resistance, making it widely applicable in aerospace and biomedical industries. However, during thermal treatments like quenching, significant distortions can occur, adversely affecting component accuracy and performance. This paper combines experimental measurements with finite element simulations to understand the deformation mechanisms and quantify the resulting distortions. The research involved heating a TC4 cylindrical specimen and quenching it in water under controlled conditions. Deformations were measured post-quenching and compared with those predicted by simulations. The results revealed that local deformation was most pronounced at the lower end of the cylinder—where cooling occurred more rapidly—and reached a value of approximately 0.54 mm. Meanwhile, macro distortion, characterized by the overall shape change of the entire cylinder, peaked at 1.63 mm. These distortions were largely driven by thermal gradients induced during quenching, with higher temperature differences leading to internal stress accumulation, plastic deformation, and eventual shape changes. The finite element model accurately captured these phenomena, predicting both temperature distributions and resultant deformations with high fidelity. Key findings also showed that the distribution of equivalent plastic strain and residual stress varied significantly along the height of the cylinder, corresponding closely with the temperature gradient. Notably, the lower portion of the cylinder—subjected to faster cooling—exhibited higher tensile stress and larger plastic strain. Conversely, the upper portion, cooling more slowly, experienced relatively less distortion. In conclusion, the study underscores the importance of understanding localized thermal and mechanical behaviors in TC4 titanium alloys during quenching. The validated simulation model offers a valuable tool for predicting and mitigating unwanted deformations in industrial heat treatment processes, supporting improved precision in the manufacturing of high-performance titanium alloy components.

83. Laser cutting of thick steel plates and simulated steel components using a 30 kW fiber laser

K. Tamura, R. Ishigami, R. Yamagishi

Department of Research and Development, The Wakasa Wan Energy Research Center, 64-52 Nagatani, Tsuruga city, Fukui prefecture, 914-0192, Japan

Journal of Nuclear Science and Technology (Taylor & Francis) IF : 1.5 (Published: 2015)

The study presents a comprehensive investigation into the capabilities of high-power laser systems for processing thick steel materials, which are commonly used in heavy industries like shipbuilding, energy, and structural engineering. Utilizing a 30 kW fiber laser, the research explored the performance of oxygen-assisted and nitrogen-assisted cutting across a variety of steel plate thicknesses, ranging from 10 mm to 60 mm, and included simulated component-like geometries to represent real-world industrial conditions. The findings demonstrated that oxygen-assisted cutting enabled effective and consistent processing of mild steel up to 60 mm thick, with optimal cutting speeds varying from 1.8 m/min for 10 mm thickness to approximately 0.35 m/min for 60 mm thickness. Kerf widths in these cuts ranged from around 0.5 mm to over 1 mm depending on thickness, and the cut surfaces remained relatively smooth with minor dross formation. For stainless steel, nitrogen-assisted cutting showed excellent results up to 40 mm thick, producing high-quality, dross-free edges. Notably, the best surface roughness (Ra) values—measured between 5 and 7 µm—were observed in thinner sections (e.g., 15 mm) cut at higher speeds, such as 1.2 m/min, though acceptable quality was maintained even as thickness increased and speeds decreased. In component-based tests, where the laser was used to cut through complex geometries resembling real industrial parts, the results confirmed high dimensional accuracy, consistent kerf geometry, and good repeatability. There were minor differences in surface quality between flat plate and component cutting, primarily due to heat accumulation and variable cutting angles, but overall the fiber laser system maintained strong performance across all tests. The study concludes that high-power fiber lasers, particularly those at or above the 30 kW range, offer robust, efficient, and high-quality solutions for cutting thick steel plates and components, paving the way for broader adoption in large-scale industrial manufacturing processes.

82. Radionuclide distribution during ytterbium doped fibre laser cutting for nuclear decommissioning

J. M. Dodds [a], J. Rawcliffe [b]

[a] National Nuclear Laboratory, Workington Laboratory, Havelock Road, Derwent Howe, Workington, Cumbria, CA14 3YQ, UK

[b] National Nuclear Laboratory, Preston Laboratory, Springfields, Salwick, Preston, Lancashire, PR4 0XJ, UK

Progress in Nuclear Energy (ELSEVIER) IF : 3.3 (Published: 2020) 

The study examines the distribution of radionuclides during ytterbium-doped fiber laser cutting of contaminated stainless steel in a simulated nuclear decommissioning scenario. Two stainless steel plates (25mm thick) were contaminated with Sr-85, Ru-106, Tc-99, and non-active Cs-133 before undergoing laser cutting at 5 kW power. The low-activity plate, cut at a length of 1.5m, exhibited volatilization losses of 42.4% Cs-133, 43.8% Sr-85, 36.9% Ru-106, and 73.2% Tc-99. The high-activity plate, subjected to a 3.0m cut length, showed higher volatilization rates: 69.9% Cs-133, 61.1% Sr-85, 53.3% Ru-106, and 88.3% Tc-99. The radionuclide distribution analysis revealed that most activity was retained within dross beneath the test piece and the local exhaust ventilation (LEV) system, with the highest levels detected in LEV filter blow-back material (1438.3 Bq Sr-85, 657.75 Bq Ru-106, and 0.4897 kBq Tc-99). Surface swabs inside and outside the LEV hood showed traces of Sr-85 (0.949 Bq) but no detectable Ru-106 or Tc-99. No Sr-85, Ru-106, or Tc-99 was found on the internal facility walls or in samples collected from the post-HEPA ventilation system. However, Cs-133, which was applied in significantly higher concentrations (200 mg per plate), was found throughout the facility, albeit at decreasing levels correlating with distance from the cutting site. The study underscores the importance of efficient ventilation and fume abatement strategies, as dross and LEV filtration systems effectively captured the majority of radionuclide emissions. These findings contribute to developing safety cases and optimizing laser-cutting technologies for nuclear decommissioning while minimizing contamination risks and airborne particulate dispersal.

81. High-power fiber laser cutting parameter optimization for nuclear Decommissioning 

A. B. Lopez [a], E. Assuncao [a, b], L. Quintino [a, b], J. Blackburn [c]

[a] IDMEC, Instituto Superior Tecnico, Universidade de Lisboa, Lisboa, Portugal

[b] European Federation for Welding, Joining and Cutting, Porto Salvo 2740-120, Portugal

[c] TWI Ltd., Granta Park, Cambridge, CB21 6AL, UK

Nuclear Engineering and Technology (ELSEVIER) IF : 2.6 (Published: 2017) 

This study shows the optimization of high-power fiber laser cutting for nuclear decommissioning, aiming to enhance efficiency and minimize material loss when cutting thick sections. A 10 kW IPGYLR-10000 fiber laser was used to cut carbon-manganese steel bars up to 70 mm thick, testing various cutting speeds (ranging from 50 mm/min to 1,500 mm/min) and nozzle configurations. The key parameters analyzed included stand-off distance (10 mm and 25 mm), focal position (0 mm and -15 mm), and beam diameter (ranging from 0.36 mm to 1.14 mm). Results indicate that focal position is the most significant factor influencing kerf width, with smaller beam diameters leading to narrower kerfs. For instance, a focal position of 0 mm resulted in a kerf width approximately 20% narrower than those achieved with CO2 and Nd:YAG lasers. Additionally, the study found that increasing specific point energy (SPE) allows for deeper cuts, with a maximum cut thickness of 70 mm achieved under optimized conditions. The material removal rate varied with thickness, peaking at 12 mm due to higher cutting speeds, but decreasing for 40 mm and 70 mm sections. Overall, the research confirms that fiber lasers are highly effective for nuclear decommissioning, offering improved cutting precision, reduced waste, and enhanced performance by fine-tuning parameters such as focal position and beam diameter.

80. In-situ immobilization technique for radioactive cesium using laser technology for Fukushima Daiichi decommissioning

H. Ozaki [a], Y. Kawahito [b, c], M. Mori [b], M. Shibata [d], , T.Nakamura [b], T. Mase [c] , H. Yoshida [f] , H. Kawakami [a, b] , M. Hori [b]

[a] Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan

[b] Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 3173-25 Showa-machi, Yokohama, Kanagawa 236-0001, Japan

[c] Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 567-0871, Japan

[d] Taiheiyo Consultant Co., Ltd., 2-4-2 Osaku, Sakura, Chiba 285-0802, Japan

[e] Faculty of Contemporary Human Life Science, Tezukayama University, 3-1-3 Gakuen-Minami, Nara 631-0034, Japan

[f]Tokyo Electric Power Services Co., Ltd. (TEPSCO), 7-12 Shinonome 1-chome, Koto-ku, Tokyo 135-0062, Japan

Materials & Design (ELSEVIER) IF : 7.6 (Published: 2025)

The study investigates an in-situ immobilization technique for radioactive cesium (Cs) using laser technology to support the decommissioning of the Fukushima Daiichi nuclear power plant. The method involves irradiating concrete samples mixed with non-radioactive 133Cs, simulating the contaminated structures at the site, using a high-brightness 500-W fiber laser. This process vitrifies the concrete, effectively trapping cesium within a stable glass matrix that can be selectively removed during decommissioning. Experimental analysis through X-ray diffraction (XRD) confirmed the vitrification process, while electron probe microanalyzer (EPMA) mapping revealed a heterogeneous but stable distribution of Cs within the fused material. The technique achieved a 99% cesium immobilization efficiency, a significant improvement over the conventional plasma melting method, which retained only 57% of Cs. Additionally, the normalized mass loss of Cs in elution tests ranged from 0.06 to 0.08 g/m², well below the ASTM International safety limit of 2 g/m², indicating strong containment properties. The study also found that the depth of vitrification decreased as the laser travel speed increased, with lower speeds yielding deeper fusion. The findings demonstrate that laser-assisted immobilization is a highly effective method for reducing radioactive waste volume while ensuring safe containment of hazardous materials. This technique offers a promising solution for efficient decommissioning efforts, minimizing long-term environmental risks associated with cesium contamination, and could significantly accelerate the Fukushima cleanup process. Future research should focus on optimizing laser parameters for large-scale applications and integrating this approach with other waste management strategies.

79. Compositional Approach to Designing FCC High-Entropy Alloys that Have an Enlarged Equiaxed Zone

M. Kang, J. Won, K. Lim, H. Kwon, S. Seo, Y. Na

Korea Institute of Materials Science, 797 Changwondae-ro, Seongsan-gu, Changwon, 

Gyeongnam 642-831

Metals (MDPI) IF : 2.6 (Published: 2018)

This study explores a compositional approach to enlarging the equiaxed zone in face-centered cubic (FCC) high-entropy alloys (HEAs) by modifying solute partitioning during solidification. The research focuses on CoCrFeMnNi HEA, where directional solidification quenching (DSQ) experiments revealed that manganese (Mn) heavily segregates into the liquid phase with a partition coefficient (Ke​) of 0.66, reducing the melting temperature at the columnar front and limiting constitutional undercooling. In contrast, chromium (Cr) partitions into the solid phase with a Ke​ ​of 1.13, increasing the melting temperature and reducing undercooling effects. To optimize undercooling and promote equiaxed grain formation, Mn and Cr concentrations were modified, and vanadium (V) was introduced at varying levels (5%, 10%, and 15%). Experimental results demonstrated that the newly designed HEAs (V5, V10, and V15) significantly increased the equiaxed zone area, with the V15 alloy exhibiting an equiaxed fraction 2-3 times higher than the original Cantor alloy. Tensile tests on pilot-scale castings further confirmed improvements, with the V15 alloy achieving a yield strength of 246-264 MPa (compared to 168-194 MPa for the Cantor alloy), tensile strength of 479-525 MPa (vs. 409-455 MPa for Cantor), and elongation of 72.8-78.7% (vs. 65.6-78.7% for Cantor). Additionally, the anisotropy index in the V15 alloy was significantly lower (3.53-4.65%) than in the Cantor alloy (5.33-9.08%), indicating improved mechanical uniformity. These findings confirm that optimizing constitutional and thermal undercooling through alloy composition adjustments effectively enhances the equiaxed zone, reduces anisotropy, and improves mechanical properties, making this approach a scalable and practical solution for enhancing HEA castings in industrial applications.

78. Significant improvement in surface hardness of CrMnFeCoNi high entropy alloy via nanosecond pulse laser grain refinement

H. Huang [a], X. Tian [a], C. Wang [a], J. Yan [b]

[a] Key Laboratory of CNC Equipment Reliability, Ministry of Education, School of Mechanical and Aerospace Engineering, Jilin University, Changchun, Jilin, 130022, China

[b] Department of Mechanical Engineering, Faculty of Science and Technology, Keio University, Yokohama, 223-8522, Japan

Vacuum (ELSEVIER) IF : 4.3 (Published: 2024)

This study explores the enhancement of surface hardness in CrMnFeCoNi high-entropy alloy (HEA) using nanosecond pulse laser grain refinement. While HEAs possess excellent mechanical properties, their low hardness limits structural applications. Traditional methods like plasma nitriding have limitations, whereas fine-grain strengthening offers a versatile alternative. Using a nanosecond fiber pulse laser (100 ns pulse width, 19.9–34.0 W power, 1.99–3.4 kW peak power), researchers irradiated CrMnFeCoNi samples, refining their grain structure and significantly increasing surface hardness. Experiment results showed a hardness improvement of 46% to 112%, with a peak hardness of 3.9 GPa (up from ~1.84 GPa). Grain sizes were reduced from 22.01 ± 26.38 μm in untreated samples to as small as 4.35 ± 3.95 μm, with refinement depths reaching up to 250 μm. Low-angle grain boundaries (LAGBs), which enhance strength, increased from 16.1% to 67.9%. X-ray diffraction (XRD) confirmed that the alloy retained its FCC phase, while energy dispersive X-ray spectroscopy (EDS) verified that the chemical composition remained unchanged. The hardness improvement was attributed to rapid heating and cooling during laser irradiation, inducing subcooling effects that promote fine grain structures. Therefore, this study demonstrates nanosecond pulse laser irradiation as an effective method to enhance HEA surface hardness without altering composition, making it a promising approach for aerospace, nuclear, and structural applications.

77. Dissimilar laser welding of an as-rolled CoCrFeMnNi high entropy alloy to Inconel 718 superalloy

D. Afonso [a], J. G. Lopes [b, c], Y. T. Choi [d], R. E. Kim [d], N. Schell [e], N. Zhou [c], H. S. Kim [d, f], J. P. Oliveira [a, b]

[a] CENIMAT/I3N, Department of Materials Science, Faculty of Sciences and Technology, Universidade NOVA de Lisboa, Caparica 2829-516, Portugal

[b] UNIDEMI, Department of Mechanical and Industrial Engineering, NOVA School of Science and Technology, Universidade NOVA de Lisboa, Caparica 2829-516, Portugal

[c] Centre of Advanced Materials Joining, Department of Mechanical & Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada

[d] Graduate Institute of Ferrous Technology, POSTECH (Pohang University of Science and Technology), Pohang 790-794, South Korea

[e] Institute of Materials Physics, Helmholtz-Zentrum Hereon, Max-Planck-Str. 1, Geesthacht D-21502, Germany

[f] Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan

Optics and Laser Technology (ELSEVIER) IF : 4.6 (Published: 2025)

This study explores the feasibility of dissimilar laser welding between an as-rolled CoCrFeMnNi high-entropy alloy (HEA) and Inconel 718 superalloy, both widely used in high-performance structural applications due to their excellent mechanical properties and corrosion resistance. A Miyachi Unitek LW50A pulsed Nd:YAG laser system was used to achieve full penetration welding under an argon protective atmosphere in a butt joint configuration. The resulting welds were free of defects such as cracks or porosity, indicating good compatibility between the two materials. Microstructural characterization using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), energy-dispersive X-ray spectroscopy (EDS), and high-energy synchrotron X-ray diffraction (SXRD) revealed distinct phase transformations across the welded region. The fusion zone (FZ) exhibited a keyhole mode morphology, and phase analysis confirmed the formation of a Laves (C14) phase, which may contribute to embrittlement. The heat-affected zone (HAZ) varied between the two materials, with Inconel 718 exhibiting a wider HAZ (approximately 265 ± 22 μm) with an average grain size of 16.4 ± 0.8 μm, whereas the CoCrFeMnNi HEA had a narrower HAZ (195 ± 33 μm) with grain sizes reaching up to 4.5 ± 0.9 μm. The chemical composition of the fusion zone reflected a mixture of both base materials, with EDS analysis showing 13.4% Co, 22.0% Cr, 19.5% Fe, 11.3% Mn, 32.7% Ni, and 1.0% Nb, suggesting dilution effects during melting and mixing. Mechanical characterization demonstrated that the welded joint exhibited an ultimate tensile strength (UTS) of 822 ± 63 MPa and a fracture strain of 7.1 ± 0.4%, which is lower than the base materials but still suitable for structural applications. Microhardness mapping revealed a hardness of approximately 220 ± 35 HV0.3 in the fusion zone, falling between the as-rolled CoCrFeMnNi HEA (343 ± 9 HV0.3) and annealed Inconel 718 (208 ± 12 HV0.3). Fracture surface analysis indicated a mixed ductile and brittle failure mode, attributed to the presence of intermetallic phases such as Laves (C14). Despite some embrittlement, the study successfully demonstrated the potential of laser welding to join these two dissimilar materials, paving the way for their use in advanced structural components where high strength and corrosion resistance are required.

76. Enhancing bonding of fresh concrete to steel through laser surface texturing   

M. Pontrandolfi [a, b], C. Gaudiuso [b], F. P. Mezzapesa [b], A. Volpe [a, b], M. Bevillon [c], A. Ancona [a, b]

[a] Intercollegiate Department of Physics “M. Merlin”, University of Bari and Polytechnic University of Bari, Via G. Amendola 173, 70125 Bari, Italy

[b] National Research Council (CNR), Institute for Photonics and Nanotechnologies (IFN), Via G. Amendola 173, 70125 Bari, Italy

[c] Gunnebo Innovation Hub, Department of Physics “M. Merlin”, Via G. Amendola 173, 70125 Bari, Italy

Surface and Interfaces (ELSEVIER) IF : 5.7 (Published: 2024)

The study investigates laser-based techniques to improve adhesion between concrete and steel, a critical factor in reinforced concrete durability. Traditional methods like sandblasting enhance roughness to improve bonding, but Laser Surface Texturing (LST) offers a more precise, contactless, and environmentally friendly alternative. The research compares Direct Laser Writing (DLW), which creates controlled micro-grooves for mechanical interlocking, and Laser-Induced Periodic Surface Structures (LIPSS), which enhances wettability to improve capillary suction. Adhesion tests on AISI 304 stainless steel samples (3 mm thick, 20 × 20 mm treated area) using a custom pull-out test revealed that untreated steel had a shear strength of 1.9 N/cm² (Sa = 0.31 µm), while LIPSS-treated surfaces increased adhesion to 3.1 N/cm² (Sa = 0.34 µm) due to enhanced wettability. Sandblasting increased adhesion strength to 4.2 N/cm² (Sa = 0.42 µm) for 20 seconds and 7.1 N/cm² (Sa = 2.50 µm) for 2 minutes, confirming that rougher surfaces promote bonding. However, DLW micro-grooves produced the best results, with longitudinal grooves (parallel to the pulling force) increasing adhesion to 8.1 N/cm² (Sa = 1.65 µm) and transversal grooves (perpendicular to the pulling force) achieving a remarkable 30.6 N/cm² (16× improvement) due to superior mechanical interlocking. Energy Dispersive X-ray Spectroscopy (EDX) detected calcium (Ca) from cement particles inside the DLW grooves, confirming the effectiveness of mechanical anchoring. These findings demonstrate that DLW, particularly with transversal grooves, is the most effective technique for improving concrete-steel adhesion, offering a precise, scalable, and chemical-free alternative to traditional methods. Optimizing laser-textured surfaces could significantly enhance the durability, structural integrity, and lifespan of reinforced concrete applications.

75. Laser dissimilar welding of CoCrFeMnNi-high entropy alloy and duplex stainless steel  

N. K. Adomako [a], G. Shin [a, b], N. Park [c], K. Park [d], J. Kim [a]

[a] Department of Materials Science and Engineering, Hanbat National University, Yuseong-gu, Daejeon, 34158, Republic of Korea

[b] Department of Materials Science and Engineering, Pusan National University, Geumjeong-gu, Busan, 46241, Republic of Korea

[c] School of Materials Science and Engineering, Yeungnam University, 280 Daehak-ro, Gyeongbuk, 38541, Republic of Korea

[d] Rare Metal R&D Group, Korea Institute of Industrial Technology, Incheon, 21999, Republic of Korea

Journal of Materials Science & Technology (ELSEVIER) IF : 11.2 (Published: 2021)  

The paper presents an in-depth study on the laser dissimilar welding of CoCrFeMnNi high-entropy alloy (HEA) and duplex stainless steel (DSS), focusing on the microstructure, mechanical properties, and the effects of post-weld heat treatment (PWHT) at 800°C and 1000°C. High-entropy alloys, known for their superior mechanical properties, corrosion resistance, and fracture toughness, are gaining traction in structural applications, particularly in the nuclear and aerospace industries. Since nuclear reactors require the joining of different materials to optimize cost and performance, welding HEAs to conventional steels such as DSS is critical. In this study, laser beam welding was chosen due to its high precision, deep penetration, and minimal heat-affected zone (HAZ), ensuring a defect-free joint with full fusion. Microstructural analysis using SEM, EDS, and XRD revealed that the weld metal (WM) retained an FCC phase without forming detrimental intermetallic compounds, microsegregation, or liquation cracks. The heat-affected zone of HEA exhibited Cr-Mn oxide inclusions, while DSS showed no such inclusions. Hardness measurements indicated that the WM had lower hardness than the base metals due to grain coarsening and recrystallization, and the application of PWHT further reduced hardness, particularly in the HEA, due to substantial grain growth. Tensile testing revealed that the as-welded joint had a strength of 584 MPa but exhibited lower ductility due to strain accumulation in the fusion zone. However, after PWHT, ductility improved significantly (by over 20%) with only a slight reduction in strength, as the deformation mechanism shifted from dislocation-dominated behavior in the as-welded joint to twinning in the heat-treated joint. Despite the overall good weldability, the joint’s lower strength compared to the base metals remains a challenge. The study suggests laser beam offset welding as a potential approach to optimize elemental distribution and refine the microstructure, which could improve mechanical properties and enhance the joint’s suitability for structural applications, particularly in nuclear power plants. Future studies will focus on optimizing welding parameters to achieve better mechanical performance.

74. Laser Beam Welding of CoCrFeNiMn-type high entropy alloy produced by self-propagating high-temperature synthesis  

K. Kashaev [a], V. Ventzke [a], N. Stepanov [b], D. Shaysultanov [b], V. Sanin [c], S. Zherebtsov [b] 

[a] Institute of Materials Research, Materials Mechanics, Department of Joining and Assessment, Helmholtz-Zentrum Geesthacht, Max-Planck-Str.1, 21502, Geesthacht, Germany

[b] Laboratory of Bulk Nanostructured Materials, Belgorod State University, Pobeda 85, Belgorod, 308015, Russia

[c] Merzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Academician Osipyan Str., 8, Chernogolovka, Moscow Region, 142432, Russia

Intermetallics (ELSEVIER) IF : 4.4 (Published: 2018) 

This study performed the laser beam welding (LBW) of a CoCrFeNiMn-type high entropy alloy (HEA) produced using self-propagating high-temperature synthesis (SHS), a process that enables the cost-effective fabrication of complex alloys. The SHS-produced HEA exhibited a face-centered cubic (fcc) structure with reduced manganese (Mn) content compared to the equiatomic CoCrFeNiMn alloy, as well as the presence of impurities such as aluminum (Al), carbon (C), sulfur (S), and silicon (Si). Microstructural analysis revealed a dendritic grain structure with columnar grains and the presence of MnS inclusions along with fine M23C6 carbides. The alloy was successfully welded using a 2-kW fiber laser at a welding speed of 5 m/min, resulting in defect-free butt joints without visible porosity or cracking. Post-weld analysis demonstrated that while the overall fcc matrix structure remained intact, significant microstructural changes occurred in the fusion zone (FZ), including a higher density of defects and the precipitation of nanoscale B2 phase particles, which were not present in the base material. These structural changes were accompanied by a substantial increase in microhardness, from 153 HV in the base material to 208 HV in the fusion zone, suggesting that B2 phase precipitation played a key role in enhancing the material’s hardness. Thermodynamic predictions using the ThermoCalc software aligned well with the experimental findings, indicating that the B2 phase precipitation was thermodynamically favorable under the rapid cooling conditions of LBW. The results of this study not only confirm that CoCrFeNiMn-type HEAs can be effectively fabricated using SHS and joined through LBW but also highlight the intrinsic hardening effect induced by the welding process, which eliminates the need for additional post-weld heat treatments. This finding has significant implications for the future development of HEAs in laser processing and additive manufacturing applications, where controlled precipitation hardening could be leveraged to enhance mechanical properties and performance in structural applications.

73. Laser Beam Welding of CoCuFeMnNi High Entropy Alloy: Processing, Microstructure, and Mechanical Properties 

J. Fiocchi [a, b], R. Casati [b], A. Tuissi [a], C. A. Biffi [a]

[a] National Research Council, CNR ICMATE, Via Previati, 23900 Lecco, Italy

[b] Department of Mechanical Engineering, Politecnico di Milano, via La Masa 1, 20156 Milano, Italy

Advanced Engineering Materials (WILEY) IF : 3.4 (Published: 2022)

This study investigates the feasibility of joining CoCuFeMnNi high entropy alloys (HEAs) using laser beam welding (LBW), analyzing process optimization, microstructural changes, and mechanical properties. The optimal welding parameters were determined to be a power of 300 W, a scanning speed of 20 mm/s, and a laser spot size of 0.45 mm. During the welding process, segregation of copper (Cu) in the melted zone (MZ) and heat-affected zone (HAZ) led to the formation of Cu-rich phases, which contributed to an overall improvement in hardness and mechanical strength. The average hardness of the welded samples was measured at 187 HV, higher than the 160 HV of the base material (BM). Microstructural analysis revealed a dendritic structure with segregated Cu-rich phases in the MZ and Cu-rich grain boundary phases in the HAZ. The welded samples demonstrated mechanical properties comparable to the base material in tensile tests, with a tensile strength of 576.4 MPa and an elongation to failure of 28.3%. Notably, fractures occurred in the base material rather than in the weld bead or HAZ, confirming the structural integrity and mechanical reliability of the welded joints. Therefore, This study demonstrates that laser beam welding is a promising technique for effectively joining HEAs in structural applications. Despite the high strength and complex metallurgy of HEAs, LBW can produce high-quality joints with excellent performance. 

72. Microstructure characterisation of multi-principal element alloys welds produced by electron beam welding

R. H. Buzolin [a, b], T. Ticther [c], F. Pixner [b], M. Rhode [c, d], D. Schroepfer [c], N. Enzinger [b]

[a] Christian Doppler Laboratory for Design of High-Performance Alloys by Thermomechanical Processing, Kopernikusgasse 24, 8010 Graz, Austria

[b] Institute of Materials Science, Joining and Forming at Graz, University of Technology, Kopernikusgasse 24/I, 8010 Graz, Austria

[c] Bundesanstalt für Materialforschung und -prüfung (BAM), Department 9. Component Safety, Berlin, Germany

[d] Otto-von-Guericke Universität, Institute for Materials Science and Joining Technology, Magdeburg, Germany

Materials & Design (ELSEVIER) IF : 7.6 (Published: 2023) 

This study systematically analyzed the microstructure and mechanical properties of CrCoNi medium-entropy alloy (MEA) and CrMnFeCoNi high-entropy alloy (HEA) after electron beam welding (EBW). MEA and HEA were prepared in cold-rolled and annealed conditions, respectively, and their welded structures were evaluated using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and energy-dispersive X-ray spectroscopy (EDX). Hardness tests were also performed to compare mechanical properties. The results showed that the fusion zone (FZ) of MEA exhibited columnar grains, with noticeable microstructural changes in the heat-affected zone (HAZ) for cold-rolled samples, whereas HAZ was negligible in annealed samples. HEA exhibited finer grain structures in the FZ compared to MEA, with a specific texture fiber in the h100 direction. Chemical analysis revealed minor elemental segregation of chromium, manganese, and cobalt in the FZ, but the impact on mechanical properties was minimal. Hardness measurements showed that MEA had higher hardness than HEA, and the FZ displayed slightly higher hardness than the annealed base metal. This study demonstrated that EBW is an effective method for defect-free welding of MEA and HEA, highlighting the influence of alloy composition and welding conditions on the microstructure and mechanical properties of welded joints. The findings provide valuable insights into the applicability of EBW for multi-principal element alloys and guidelines for microstructural control.

71. Improvement of microstructure and performance of an extreme-high-speed laser cladding CoCrFeMnNi coating through laser shock peening

J. L. Du [a], W. W. Deng [a], X. Xu [a], Y. J. Wu [a], K. Y. Luo [a], H. M. Zhang [a], and J. Z. Lu [a]

[a] School of Mechanical Engineering, Jiangsu University, Zhenjiang, 212000, PR China

Journal of Alloys and Compounds (ELSEVIER) IF : 5.8 (Published: 2024)

This study utilized LSP as a post-treatment technique for CoCrFeMnNi HEA coatings prepared via EHLC. The impact of LSP on the microstructural characteristics of extreme-high-speed laser cladding (EHLC) HEA coatings was meticulously examined, and their wear and corrosion behaviors were analyzed. This investigation provides insights into the feasibility of establishing LSP as an effective post-treatment process for EHLC HEA coatings. This study achieved the infrared nanosecond pulse laser used for LSP through Q-switching. The output laser parameters were configured with a frequency of 5 Hz, wavelength of 1064 nm, and pulse duration of 10 ns. After LSP treatment, the phase of the EHLC CoCrFeNiMn coating did not change and remained FCC phase. EBSD and TEM analyses show that LSP introduced strong plastic deformation in the EHLC CoCrFeMnNi coating, producing a large number of LAGBs, high-density dislocations, and deformation twins. The grain size decreases with the increase in the shock number. After four LSP treatments, the average grain size is reduced from 22.39 μm to 13.39 μm. The depth affected by LSP significantly exceeds the thickness of the EHLC HEA coatings deposited in this study (approximately 200 μ m). Both the coating surface and the underlying 316 L stainless steel substrate exhibit grain refinement under the influence of LSP-induced shock waves. The strengthening effect on EHLC CoCrFeMnNi coatings in creases with the cumulative applications of LSP. Furthermore, the accumulated tensile stress inside the EHLC HEA coating is converted into compressive residual stress, with a maximum value of 141.5 MPa. The hardness of the untreated EHLC coating is uniform, with an average hardness of 225.8 HV. After one and four LSP treatments, the average surface microhardness significantly increases to 287.3 HV and 341.8 HV, respectively, demonstrating increases of 29.0% and 51.9%. The improvement in microhardness and wear resistance after LSP is attributed to the combined effect of Hall-Petch and Taylor hardening strengthening. The sample showed better wear resistance after LSP treatment. With a 12 N load, the wear rate for the LSP-4 specimen decreases by 62.8 % relative to the untreated EHLC specimen. It can be seen that the abrasion loss and friction coefficient are always smaller when the specimen was LSP treated compared to that untreated, which is due to the increased hardness in the surface layer of the specimen induced by LSP treatment. Electrochemical analysis reveals that LSP- treated specimens exhibit lower I_corr and higher E_corr, evidencing enhanced corrosion resistance. The residual stress and grain refinement induced by LSP are the reasons for improving corrosion resistance. This study provides a promising post-treatment method for improving the performance of CoCrFeMnNi HEA coatings prepared by EHLC. 

70. Combination of annealing and laser shock peening for tailoring microstructure and mechanical properties of laser directed energy deposited CrMnFeCoNi high-entropy alloy

Z. Tong [a, b], W. Wan [b], H. Liu [b], W. Zhou [b], Y. Ye [a, b] and X. Ren [b]

[a] Institute of Micro-nano Optoelectronics and Terahertz Technology, Jiangsu University, Zhenjiang, 212013, PR China

[b] School of Mechanical Engineering, Jiangsu University, Zhenjiang, 212013, PR China

Additive Manufacturing (ELSEVIER) IF : 10.3 (Published: 2023)

In this work, a combined post-treatment of annealing and LSP was performed on LDED-prepared CrMnFeCoNi HEA. The microstructure and tensile properties of LDED-prepared specimens before and after post-treatment were comparatively studied and the respective effects of annealing and LSP on improving the mechanical properties were clarified. A Q-switched Nd:YAG laser equipment was chosen for the LSP process. LSP experiments were conducted in the air condition under 25°C and the process parameters are set under the following conditions: repetitions rate of 5 Hz, pulse width of 10 ns, laser energy of 6 J, and LSP impact times of 3. After LSP experiments, compared to the pristine as-built specimen directly subjected to LSP, the strengthening effect of the combination of annealing and LSP was more evident owing to the increase in plasticity of the as- built specimen caused by annealing. Higher amplitude and deeper compressive residual stresses were formed in the surface layer of the annealed specimen than that of a pristine as-built specimen. LSP refined coarse grains on the surface of the annealed specimen into nano-scale grains and created high-density dislocations and deformation twins, resulting in an improvement in the strength and hardness of annealed+LSP specimen. The dislocation network annihilation and thermal stress relaxation caused by annealing, as well as LSP-induced strain gradient and compressive residual stress, contributed to the excellent ductility of the annealed+LSP specimen. 

69. Microstructure, microhardness and residual stress of laser additive manufactured CoCrFeMnNi high-entropy alloy subjected to laser shock peening

Z. Tong [a], H Liu [a], J. Jiao [a], W. Zhou [a], Y. Yang [a] and X. Ren [a]

[a] School of Mechanical Engineering, Jiangsu University, Zhenjiang, 212013, PR China

Journal of Materials Processing Technology (ELSEVIER) IF : 6.7 (Published: 2020)

In this study, LSP is used to modify the surface of CoCrFeMnNi HEA, and study the effect of LSP on the microstructure and mechanical performances. The subsurface residual stress and microhardness distribution along depth direction are measured before and after LSP. The microstructure evolution of CoCrFeMnNi HEA during LSP is examined and discussed. An underlying grain refinement mechanism of CoCrFeMnNi HEA during ultrahigh strain rate plastic deformation is systematically revealed. This work aims to provide a novel surface strengthening method for achieving high-performance CoCrFeMnNi HEA. A Q-switched Nd:YAG laser system was used to do LSP experiments under the following conditions: repetition rate of 5 Hz, wavelength of 1064 nm, and pulse width of 10ns. During LSP experiments, a 1 mm-thick running water layer and 100 um-thick aluminum foil worked as a confining layer and protective layer, respectively. The microhardness clearly increases after LSP and the surface strengthening effect significantly increases with increasing laser energy. The stress state in the subsurface transforms from tensile into com pressive after LSP and the stress amplitude increases upon increasing the laser energy. Nanograins are obtained at the top surface of the CoCrFeMnNi HEA after multiple LSP treatments. The microstructure evolution process is discussed and a grain refinement mechanism during LSP is proposed, which can be explained as follows: (1) formation of high-density dislocation structures at low strain, involving DTs, DWs and DCs, (2) concurrent NBs and MTs aligned in one direction divide the matrix into T/M and NB/M lamellae structures, (3) activation of two twinning systems and two-direction aligned NBs contribute to NB-NB, MT-MT and MT-NB interactions, which divide the matrix into nanoscale rhombic blocks, (4) transition of sub-grains generated by three-types of interactions into homogeneous equiaxed nanograins via dynamic recrystallization. The surface strengthening mechanism related to the gradient microstructure characteristic is proposed. 

68. Surface strengthening of single-crystal alumina by high-temperature laser shock peening 

Fei Wang [a], Xueliang Yan [a], Lei Liu [b], Michael Nastasi [c], Yongfeng Lu [b] and Bai Cui [a]

[a] Department of Mechanical & Materials Engineering, University of Nebraska–Lincoln, Lincoln, NE, USA

[b] Department of Electrical & Computer Engineering, University of Nebraska–Lincoln, Lincoln, NE, USA

[c] Department of Nuclear Engineering, Texas A&M University, College Station, TX, USA

Materials Research Letters (Taylor & Francis, 2021)

Single-crystal alumina (sapphire) is a critical structural and optical ceramic due to its excellent light transmission, chemical resistance, superior mechanical properties, and high thermal stability. Despite its benefits, sapphire has low fracture toughness, making it prone to cracking and mechanical failure. Traditional strengthening methods for ceramics (e.g., ceramic-matrix composites, transformation toughening) cannot be applied to single-crystal ceramics because they alter the material's phase composition or optical properties. Methods like solid solution strengthening, precipitation strengthening, and neutron irradiation also have limitations, such as reduced optical transmittance or safety concerns. Laser Shock Peening (LSP) is a surface engineering technique that improves mechanical properties by inducing compressive residual stress. While it has shown success in poly-crystalline ceramics, applying LSP to single-crystal ceramics is challenging due to potential surface damage from laser-induced shock waves. Therefore, the study introduces a novel high-temperature laser shock peening (HTLSP) process, hypothesizing that performing LSP above the brittle-to-ductile transition (BDT) temperature (1030–1100°C for sapphire) can induce plastic deformation and strengthen single-crystal ceramics without significant surface damage. As a result, high-temperature laser shock peening at 1200 °C is demonstrated as a novel and effective method for strengthening the surface of single-crystal ceramics. HTLSP significantly reduces surface damage from shock waves compared to conventional room-temperature LSP, enabling enhanced mechanical properties while maintaining the material’s optic properties. The treated sapphire retains 98.6% of its original optical transmittance. Also, HTLSP induces a compressive residual stress of about 1 GPa on the surface, leading to 29% increase in fracture toughness, 9% increase in microhardness, and 18% increase in nano-hardness. TEM analysis reveals a high density of dislocations on basal slip planes near the surface, extending to a depth of more than 10 um. These dislocations result from plastic deformation activated by high shock wave pressure at 1200 °C. In conclusion, HTLSP provides a promising strategy for strengthening single-crystal ceramics without sacrificing their optical properties, offering potential applications in industries requiring durable and optically transparent materials.

67. Laser cutting study on 30 mm thick stainless steel for application in decommissioning of calandria shells in heavy-water reactors

J. Shin [a, b]

[a] Quantum Optics Research Division, Korea Atomic Energy Research Institute, 111 Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon, 34057, Republic of Korea

[b] Department of Radiation Science, University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon, 34113, Republic of Korea

Nuclear Engineering and Technology (ELSEVIER) IF : 2.6 (2024) 

This study was entirely focused on cutting 30 mm thick stainless steel. Cutting tests were conducted using heads with various focal lengths to determine the proper cutting speed for each focal length, and the amount of secondary waste generated was also evaluated. They used a 6-kW ytterbium-doped fiber laser as the cutting light source. Four different types of cutting heads were employed, all of which were developed. They were also made from single fused silica with anti-reflective coatings to minimize power absorption by the lenses. 304L stainless steel, the primary material of the calandria shell, was used as the cutting material. Specimen 1 was used in the cutting tests to measure the maximum cutting speed, the amount of secondary waste, and for the change-of-direction cutting test. Specimen 2 was used for long-length cutting. Using the laser head, 30 mm thick stainless steel was successfully cut at a high-speed exceeding 250 mm/min. At this cutting speed, the average kerf width was 1.18 mm, and the amount of secondary waste generated was 279.5 g/m. The head was also used successfully for change-of direction and long-length cutting, with all cuts being completed without any failures when the proper speed was applied. These results are expected to provide valuable data for future applications of laser cutting on calandria shells in heavy-water reactor decommissioning projects.

66. Martensitic transformation in temporally shaped femtosecond laser shock peening 304 steel 

Y. Lian [a, b], Y. Hua [a, b], J. Sun [a, b], Q. Wang [a, b], Z. Chen [a, b], F. Wang [a, b], K. Zhang [a, b], G. Lin [a, b], Z. Yang [c], Q. Zhang [c], and L. Jiang [a, b, *]

[a] Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, PR China

[b] Beijing Institute of Technology Chongqing Innovation Center, Chongqing 401120, PR China

[c] Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, PR China

Applied Surface Science (ELSEVIER) IF : 6.3 (2021)

In this study, They conducted temporally shaped fs-LSP on 304 stainless steel and calculated the thermoelastic wave-spreading process. They adjusted the pulse delay from 5 to 50 ps and the laser fluence from 40 to 800 J/cm^2; the hardness of the laser-peened sample increased by 20% for a double-pulse delay of 20 ps and a laser fluence of 400 J/cm^2. The test results indicated that martensitic transformation, and not grain refinement, was the main underlying reason for hardness improvement. By analyzing the time-resolved shadowgraph images and simulation results, they identified electron dynamics, such as temperature and density, as the main factors affecting energy transfer and stress propagation. As a result, they achieved more than 20% improvement in hardness under a laser fluence of 400 J/cm^2 and a pulse delay of 20 ps. The XRD and EBSD results indicated that the martensitic transformation and its related residual compressive stress should be the main contributors to surface strengthening. In the case of the energy absorption and mechanical response mechanism, the decreased electron temperature during plasma expansion meant a lower energy conversion rate. Plasma expansion also meant decreased plasma electron density, which led to higher laser transmission and lower reflectivity. Therefore, with a suitable double-pulse delay of 20 ps, the plasma with a higher temperature could propagate stronger compressive stress toward the interior material, which easily induces martensitic transformation. The results provide novel insight into structural transformation and surface strengthening by temporally shaped fs laser.

65. Investigation on femtosecond laser shock peening of commercially pure copper without ablative layer and confinement layer in air

L. Chen, Z. Wang, S. Gao, L. Zhu, W. Yu, and H. Zheng

Centre for Advanced Laser Manufacturing (CALM), Shandong University of Technology, Zibo, 255000, PR China

School of Mechanical Engineering, Shandong University of Technology, Zibo 255000, PR, China

School of Materials Science and Engineering, Shandong University of Technology, Zibo 255000, PR China

Optics and Lasers in Engineering (ELSEVIER) IF : 3.5 (2022)

Laser shock peening using a femtosecond laser of commercially pure copper without an ablative layer and confinement layer in the air was investigated in detail. An Yb:KGW femtosecond laser source was employed to perform fs-LSP in this experiment. The effect of laser pulse energy on fs-LSP was evaluated by surface morphology, chemical composition, surface roughness, microstructure, residual stress, and microhardness, and the relevant mechanism of surface modification was discussed. As a result, When pulse energy is low, material removal and plastic deformation occur simultaneously, and regular dents are produced at the sample surface. With the increase of pulse energy, the laser ablation effect is accompanied by laser melting, surface oxidation, and a macro ripple structure appearing at the top surface. After fs-LSP, the surface roughness increases obviously. With the increase of pulse energy, the increase of surface roughness becomes not very significant. When pulse energy reaches 28 μJ, copper oxide forms at the treated surface. A grain refinement layer is detected by XRD analysis and nano-indentation tests, and an affected thickness of about 5 µm for fs-LSP on copper is indicated. The untreated sample exhibits an initial surface residual compressive stress of about 23.0 ± 9.7 MPa, which is greatly improved by fs-LSP. With the increase of pulse energy, the residual compressive stress gradually increases to a maximum 108.3 ± 10.8 MPa at 51 μJ. With the increase of pulse energy, the surface microhardness firstly increases from the untreated 113.32 ± 1.45 HV to a maximum 127.34 ± 3.42 HV by 12.4% at 28 μJ, and then experiences a slight decrease.

64. Laser cutting of steel plates up to 100 mm in thickness with a 6-kW fiber laser for application to dismantling of nuclear facilities

J. Shin, S. Oh, H. Park, C. Chung, S. Seon, T. Kim, L. Lee, and J. Lee

Korea Atomic Energy Research Institute, 111, Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon 34507, Republic of Korea

Optics and Lasers in Engineering (ELSEVIER) IF : 3.5 (2018)

A cutting study with a 6-kW ytterbium-doped fiber laser was conducted for stainless steel and carbon steel plates having various thicknesses. The maximum cutting speeds for various thicknesses were obtained to evaluate the cutting performance. As representative results, the maximum cutting speeds for a 60-mm thickness were 72 mm/min for the stainless steel plates, and 35 mm/min for the carbon steel plates, and those for a 100-mm thickness was 7 mm/min for stainless steel plates and 5 mm/min for carbon steel plates. The results of this work show an efficient cutting capability of 16.7 mm by kW, whereas the results of other groups have shown a cutting capability of ∼10 mm by kW. In addition, the maximum cutting speeds were faster for the same thicknesses than those from the other groups. The kerf width, another important characteristic, was also measured to determine the amount of secondary waste in the dismantling of a nuclear facility. For the cutting of 60-mm and 100-mm thick steels, the front kerf widths were ∼1.0 mm for all cases, and the rear kerf widths were larger than the front kerf widths but as small as a few millimeters. The experiment results showed that a steel plate of up to 100 mm in thickness can be cut at a laser power of 6-kW. However, a cutting speed of 7 mm/min or 5 mm/min for a thickness of 100 mm was shown to be too low for field application in the dismantling of a nuclear facility. Therefore, a higher power laser with the order of 10-kW is required in a field application, which was expected to be capable of cutting with a high speed of several millimeters per minute for a thickness of 100 mm with our system.

63. Laser cutting studies on 10 - 60 mm thick stainless steels with a short focus head for nuclear decommissioning 

J. Shin, K. Song, S. Oh, and S. Park

Korea Atomic Energy Research Institute, 111, Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon 34507, Republic of Korea

Optics & Laser Technology (ELSEVIER) IF : 4.6 (2024)

In this work, a cutting head was fabricated using a focusing element with a focal length half that of our previous head. Laser cutting studies with this head were performed on stainless steel plates with thicknesses ranging from 10 to 60 mm. Additionally, the cutting performance was evaluated based on changes in laser power, a factor that should have been investigated in our previous works. The maximum cutting speed for each plate thickness was measured and summarized as a representative performance indicator. Furthermore, the kerf width for each thickness was measured to evaluate the amount of secondary waste generated during the cutting process. In cutting capability, despite the relatively short focal length of 300 mm, the cutting system demonstrated the ability to achieve cuts on stainless steel plates up to a thickness of 60 mm at a laser power of 6 kW. The cutting capability was estimated at 10 mm/kW. These experiments included both constant speed-cutting and two-step speed-cutting approaches. Firstly, constant speed cutting demonstrated better maximum cutting speeds. However, for thicknesses greater than 10 mm, two-step speed cutting is better than constant speed cutting. Based on these results, two-step cutting achieved a more than twofold increase in maximum cutting speed for these thicker plates. In correlation with the kerf width secondary waste, the amount of secondary waste was calculated based on the kerf width, and it was determined that the cutting process generated a relatively small amount of secondary waste.

62. High-speed fiber laser cutting of thick stainless steel for dismantling tasks

J. Shin, S. Oh, H. Park, C. Chung, S. Seon, T. Kim, L. Lee, B. Choi, and J. Moon

Korea Atomic Energy Research Institute, 111, Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon 34507, Republic of Korea

Optics & Laser Technology (ELSEVIER) IF : 4.6 (2017)

This paper contains the design of the developed laser cutting head and the recent experimental results of the high-speed cutting of thick stainless steel plates with this head and a high-power fiber laser. Experimental studies of laser cutting were accomplished using a developed cutting head and a 6 kW fiber laser. As a representative experimental result of this work, a 60 mm thick stainless steel plate was cut with a maximum speed of 72 mm/min. To the best of our knowledge, this cutting speed is the highest when cutting 60 mm thick stainless steel with a 6 kW laser power. The successful high-speed cutting experimental results in this work proved that our laser cutting system and cutting conditions were more efficient than those of other groups. Our system also achieved a narrow kerf width. The measured kerf width of the front side was as small as 0.82 mm, and that of the rear side was also as small as 1.70 mm. In general, it has been known that the cutting capability of steel is about 10 mm per kW. Thus, based on this knowledge, a 10 kW laser power is necessary to cut to a thickness of 100 mm. However, it was expected that the experimental results show the possibility of a thicker cutting of more than 60 mm. From the trend of the maximum cutting speed, it was predicted that about a 100 mm thick steel plate can be cut with a speed of several mm/min even when applying a low laser power of 6 kW.

61. Improvement of microstructure and performance of an extreme-high-speed laser cladding CoCrFeMnNi coating through laser shock peening 

J. L. Du, W. W Deng, X. Xu, Y. J. Wu, K. Y. Luo, H. M. Zhang, and J. Z. Lu

School of Mechanical Engineering, Jiangsu University, Zhenjiang 212000, PR China

Journal of Alloys and Compounds (ELSEVIER) IF : 5.8 (2024) 

This study utilized laser shock peening (LSP) as a post-treatment technique for CoCrFeMnNi HEA coatings prepared via EHLC. An infrared nanosecond pulse laser used for LSP through Q-switching was applied to the experiments. The impact of LSP on the microstructural characteristics of EHLC HEA coatings was meticulously examined, and their wear and corrosion behaviors were analyzed. This investigation provides insights into the feasibility of establishing LSP as an effective post-treatment process for EHLC HEA coatings. After LSP treatment, the phase of the EHLC CoCrFeNiMn coating did not change and remained in the FCC phase. EBSD and TEM analyses show that LSP introduced strong plastic deformation in the EHLC CoCrFeMnNi coating, producing a large number of LAGBs, high-density dislocations, and deformation twins. The grain size decreases with the increase in the shock number. The accumulated tensile stress inside the EHLC HEA coating is converted into compressive residual stress, with a maximum value of 141.5 MPa. The hardness of the untreated EHLC coating is uniform, with an average hardness of 225.8 HV. The sample showed better wear resistance after LSP treatment. It can be seen that the abrasion loss and friction coefficient are always smaller when the specimen was LSP treated compared to that untreated, which is due to the increased hardness in the surface layer of the specimen induced by LSP treatment. 

60. An efficient laser decontamination process based on non-radioactive specimens of nuclear power materials

Y. Hu a,b, C. Liu a, K. Li a, J. Cheng c, Z. Zhang b and E. Han b

a Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China

b Institute of Corrosion Science and Technology, Guangzhou 510530, China

c Laser Group, School of Mechanical Engineering, Hubei University of Technology, Wuhan 430068, China

Materials (MDPI) IF : 3.1 (2023)

The process of laser decontamination of the oxide layer on the surface of non-radioactive specimens prepared under simulated one-loop aqueous chemical conditions was investigated using a pulsed fiber laser. A process with a high decontamination efficiency was explored, and the decontamination results were evaluated. In addition, the effect of different laser power levels on the surface morphology of the material, as well as on the elemental composition, was studied. The results show that the decontamination efficiency reached 10.8 m2/h under the conditions of a pulse width of 500 ns, a laser repetition frequency of 40 kHz, a scanning speed of 15,000 mm/s, and a line spacing of 0.2 mm, according to which the removal effect was achieved when the laser power was 160 W, and the oxygen content on the surface was 6.29%; additionally, there were no oxide phases in the XRD spectra after decontamination. Therefore, the laser cleaning process without spot overlap can provide a reference for future practical operations to remove radioactivity from nuclear power components efficiently.

59. Cutting performance of thick steel plates up to 150 mm in thickness and large size pipes with a 10-kW fiber laser for dismantling of nuclear facilities

Jae Sung Shin, Seong Yong Oh, Hyunmin Park, Chin-Man Chung, Sangwoo Seon, Taek-Soo Kim, Lim Lee, Jonghwan Lee

Korea Atomic Energy Research Institute, 111, Daedeok-daero 989 beon-gil, Yuseong-gu, Daejeon 34057, Republic of Korea 

Annals of Nuclear Energy (ELSEVIER) IF : 1.9 (2023)

In this study, attempts were made to cut 100 mm thick stainless steel and carbon plates at high speeds by introducing a 10 kW fiber laser, considering the 10 mm steel cutting capability per kW commonly known in laser cutting. The cutting performance up to 100 mm in thickness was evaluated for high-speed cutting of thickness of 100 mm, both stainless steel and carbon steel plates were cut at maximum cutting speeds of ~ 30 mm/min. In addition, the cut specimens showed narrow kerf shapes with front and rear kerf widths of less than 5 mm. A 150 mm thick stainless steel plate was attempted to be cut, based on the fact that previous work showed a cutting capability of ~ 15 mm per kW when using cutting head. The cutting thickness of 150 mm is the largest with a laser power of 10 kW. Large sized stainless steel pipes were also attempted to be cut. A 165 mm diameter pipes was able to be cut at a high speed using a single scan at a speed of 50 mm/min and a round trip scan at a speed of 100 mm/min. In conclusion, the cutting showed narrow kerf widths of less than 5 mm even for very thick steel of up to 150 mm in thickness. Although not expressed on the result and discussion section, the cutting performance was almost same in several attempts.

58. Laser cutting study of zirconium alloys for nuclear decommissioning 

J. Shin a,b, J. Ock c, S. Choi c,d

aQuantum Optics Research Division, Korea Atomic Energy Research Institute, 111 Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon 34057, Republic of Korea

bDepartment of Radiation Science, University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea

cDepartment of Nuclear Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

dInstitute of Engineering Research, Seoul National University, 1 Gwanak-ro, G wanak-gu, Seoul 08826, Republic of Korea

Nuclear Engineering and Technology (ELSEVIER) IF : 2.6 (2023) 

A laser cutting study on zirconium alloys, specifically Zircaloy-2 and Zr-2.5%Nb alloy, which are used as constituent materials in the fuel channels of CANDU 6 type PHWR is conducted. Each zirconium alloy exhibited the same maximum cutting speed, which was 1.7-1.9 times higher than that of SS304L. Additionally, the amount of secondary emissions per unit length of zirconium alloys when cut at a thickness of 10 mm ranged from 32-53 g/m, representing about 60-70% of that of stainless steel. Zircaloy-2 and Zr-2.5%Nb alloy showed similar aerosol characteristics. The CMAD for both alloys was approximately 0.25 μm, 15-17% larger than that of SS304L, indicating that zirconium alloys generated larger particles. Moreover, fewer particles smaller than 0.5 μm were generated from the cutting of zirconium alloys compared to SS304L. The total number concentrations of zirconium alloys were 16-18% higher than that of SS304L stainless steel. It means that more aerosols were generated during the cutting of zirconium alloys compared to SS304L. This result would only aid in designing and implementing effective aerosol collection and removal systems but also play a crucial role in significantly minimizing exposure risks, thereby enhancing workplace environmental safety and protecting worker health.

57. Experimental investigation of underwater laser cutting for thick stainless steel plates using a 6-kW fiber laser 

Seong Y. Oh , Jae Sung Shin, Seungkyu Park, Sungok Kwon, Sungmo Nam, Taeksoo Kim, Hyunmin Park, Jonghwan Lee 

Korea Atomic Energy Research Institute, 111, Daedeok-daero 989 beon-gil, Yuseong-gu, Daejeon 34057, Republic of Korea 

Annals of Nuclear Energy (ELSEVIER) IF : 1.9 (2023)

In this study, we cut stainless steel blocks with the thickness of 50, 60, 70, and 80 mm into two pieces to obtain a more accurate value of mass loss by removing the debris remaining inside the kerf, except for the dross adhering to the cutting surface. The kerf width was calculated based on the mass loss information, inherent density values of the employed stainless steels, and the cutting surface area. Furthermore, the mass loss per cut length was calculated to assess the amount of secondary emission for each laser-cut block under the assumption of neglecting the mass gained by the dross owing to the oxidation process. In underwater cutting, reducing the buoyancy effect acting on the submerged gas jet is an important step for increasing the permissible thickness to be cut completely using a laser. Therefore, a dual nozzle was used to reduce the buoyancy effect. The results demonstrated the capability of completely cutting out the steel blocks with a thickness of 50, 60, 70, and 80 mm into two pieces. In addition, the mass of secondary waste without considering the oxidation process was estimated to be 475, 517, 632, and 750 g/m, respectively. The average kerf widths, regardless of cutting route and specimen thickness, were measured to be narrower in the range of 1.1–1.2 mm. The narrower kerf width is mainly achieved by the smaller diameter of the laser beam radiated on the top plate surface. The kerf widths were approximately twice as large as the laser beam diameter of 647 μm. Our experimental results prove that the laser cutting tool has the capability of reducing the kerf width, which in turn can release lower secondary waste than other approaches, such as the water-jet, plasma arc, and mechanical cutting. The bubble trains that inevitably occur in the thermal cutting process interrupt the observation of the front face where the steel block is cut. This obstruction was significantly improved by monitoring the cutting process at the rear face of the specimen to avoid bubble trains. 

56. Ultra high power laser cutting of 1-m reinforced concrete with gravity

Yosuke Kawahito a b, Hitoshi Ozaki c, Michiko Mori a, Yuya Kino d, Tsuyoshi Nakamura a, Hiroyuki Yoshida e, Hiroshi Kawakami a c, Muneo Hori a 

aJapan Agency for Marine-Earth Science and Technology (JAMSTEC), 3173-25 Showa-machi, Yokohama, Kanagawa 236-0001, Japan

bGraduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 567-0871, Japan

cGraduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan

dARK Information Systems, INC., 4-2 Goban-cho, Chiyoda-ku, Tokyo 102-0076, Japan

eTokyo Electric Power Services Co., Ltd. (TEPSCO), 7-12 Shinonome 1-chome, Koto-ku, Tokyo 135-0062, Japan

Optics and Lasers in Engineering (ELSEVIER) IF : 3.5 (2023)

Lasers are an excellent source of directed energy. In this study, we developed a novel cutting method for reinforced concrete (RC), enabling separation of brittle RC vitrified by ultra-high-power laser ranging from 30 to 60 kW in power. The input laser energy, ranging from 13 to 124 mJ, was initially used to cut RC of 0.5 or 1 m in length without assist gas. Instead of the assist gas, the molten concrete was pulled down by gravity. Vitrification of the RC occurred under all conditions. A 50-kW laser with an energy of 43 mJ successfully penetrated 1-m RC by elevating the laser with focal reciprocation along the optical axis at a travel speed of 6 mm/min. The maximum fusing volume achieved was 5.19 × 106 mm3 with an energy input of 109.2 mJ. The average fusing volume per unit energy input was 46.7 mm3/kJ, which is approximately 1.2 times more efficient than that for carbon steel. Voids and cracks were observed at the boundary between the concrete and the vitrification, aiding in melting and separating the RC. Numerical analysis revealed that the through hole generated by burn-through concrete allows the laser to propagate inside the molten concrete. This study validates the potential outdoor application of ultra-high-power lasers, including cutting during the decommissioning of Fukushima. 

55. Continuous wave laser grooving of cementitious materials 

M. Rupp a, b, S. Hayashi a, b, c, C. Dashe a, b, S. Gupta b, d, R. Moini b, d, C. B. Arnold a, b 

aDepartment of Mechanical and Aerospace Engineering, Princeton University, Olden St., Princeton, NJ, 08544, USA

bPrinceton Institute for the Science and Technology of Materials, Princeton University, Prospect Ave., Princeton, 08540, USA

cSchool of Integrated Design Engineering, Keio University, 3-14-1, Hiyoshi, Kohoku-ku, Yokohama, Kanagawa, 223-8522, Japan

dDepartment of Civil and Environmental Engineering, Princeton University, Olden St., Princeton, NJ, 08544, USA

Applied Physics A (Springer) IF : 2.5 (2023) 

In this work, they explore the use of continuous wave laser processing to create V-shaped grooves in hardened cement paste at fixed laser power with different laser scanning speeds. They find that the laser process can produce the desired sharp notches with steep side walls under the correct processing conditions. Recast and restructuring of the groove sidewalls create bridges within the notch that can potentially be detrimental to the microstructure or lead to inaccurate fracture properties. The effects of laser processing on the microstructure are investigated using SEM and confocal microscopy. First, they fabricated the cement paste samples using OPC with a water-to-cement ratio of 0.275 based on previous studies. YLR-400-AC has a maximum power of 400 W with a beam diameter of 100 um. The laser irradiation was set to the maximum power, while the rastering speed was varied between 15 and 50 mm/s. Through control over laser processing parameters, it is possible to control the notch width and depth, all while maintaining a clear V-shaped groove in the material. As the scanning speed decreases, the depth and the width increase until a critical speed is reached. Below that speed, the laser process is unable to remove all the material cleanly and creates resolidified bridges across the groove that structurally supports the notch. In this study, with a 400 W laser, the critical scanning speed is 35 mm/s, which results in a 4 mm deep x 0.75 mm wide and clear groove across the sample. It is expected that higher-power lasers would enable much faster speeds, leading to a precise and commercially viable laser-based approach for creating grooves and engineered defects in concrete and other brittle or quasi-brittle infrastructure materials.

54. Improving the ductility in laser welded joints of CoCrFeMnNi high entropy alloy to 316 stainless steel 

J.P. Oliveira a g, A. Shamsolhodaei b, Jiajia Shen a, J.G. Lopes a, R.M. Gonçalves a, Mariana de Brito Ferraz g, Lourenço Piçarra a, Z. Zeng c, N. Schell d, N. Zhou b, Hyoung Seop Kim e f  

aUNIDEMI, Department of Mechanical and Industrial Engineering, NOVA School of Science and Technology, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal

bCentre of Advanced Materials Joining, Department of Mechanical & Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada

cSchool of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Sichuan 611731, China

dHelmholtz-Zentrum Hereon, Institute of Materials Physics, Max-Planck-Str. 1, Geesthacht 21502, Germany

eDepartment of Materials Science and Engineering, POSTECH (Pohang University of Science and Technology), Pohang 37673, South Korea

fInstitute for Convergence Research and Education in Advanced Technology, Yonsei University, Seoul, 03722, South Korea

gCENIMAT/I3N, Department of Materials Science, NOVA School of Science and Technology, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal

Materials & Design (ELSEVIER) IF : 7.6 (2023) 

In this study, laser welding of an annealed CoCrFeMnNi high entropy alloy to 316 stainless steel is accomplished. By changing the high entropy alloy condition, the joint ductility was significantly improved without a strength decrease. The microstructure evolution of the joint is studied by electron microscopy and high-energy synchrotron X-ray diffraction coupled with high throughput thermodynamic calculations. Mechanical testing aided by digital image correlation allowed to correlate the microstructure effects on the joint mechanical performance. This approach can be used for dissimilar combinations where there is no need to increase the joint strength, but the aim is to increase its ductility. Differences between thermodynamically predicted phases and those observed in the material may be explained by the significant non-equilibrium conditions associated with laser welding, where the large undercooling and the slow kinetics associated with the sigma phase prevent its formation within the fusion zone. Despite the deformation across the joint being more homogenous, as the difference in hardness across the joint is less than 50 HV, the large columnar grains in the fusion zone will eventually allow for massive strain accumulation to occur at this region, which ultimately leads to joint failure. Mixed features of ductile and brittle failure were observed in the fracture surfaces of the joint. These mixed features may indicate that certain compositional ranges within the Co-Cr-Fe-Mn-Ni system may present ductile or brittle behavior even though a fully FCC structure was observed in the fusion. The hardness gradient observed across the welded joint can be correlated to the strength of individual compositions, suggesting the potential to obtain high-strength materials in the as-cast condition in the Co-Cr-Fe-Mn-Ni system. 

53. Analysis of nano-particle release from the surface of structural concrete members by laser ablation using soft computing 

Zibing Su a, Rui Wang b, Dalibor Petković c, Nebojsa Denic d, Riadh Marzouki e, Mohamed Amine Khadimallah f g 

aArt College of Chongqing Technology and Business University, Chongqing 400067, China

bSchool of Smart City Design, Chongqing Jianzhu College, Chongqing 400072, China

cUniversity of Niš, Pedagogical Faculty in Vranje, Partizanska 14, 17500 Vranje, Serbia

dUniversity of Priština in Kosovska Mitrovica, Faculty of Sciences and Mathematics, Serbia

eChemistry Department, College of Science, King Khalid University, Abha 61413, Saudi Arabia

fPrince Sattam Bin Abdulaziz University, College of Engineering, Civil Engineering Department, Al-Kharj, 16273, Saudi Arabia

gLaboratory of Systems and Applied Mechanics, Polytechnic School of Tunisia, University of Carthage, Tunis, Tunisia

Optical & Laser Technology (ELSEVIER) IF : 4.6 (2023) 

In this study, the findings of ablation experiments on cement and concrete member specimens were performed with a fiber laser. In order to know the influence of substrate composition on the ablation ratio and processes, the laser-surface interaction was examined on type I portland cement with varying amounts of sand or fine silica. The purpose of this study is to use an adaptive neural fuzzy inference system (ANFIS) to categorize multiple input variables for material removal rate (MRR) and ratios based on process variables. particles formed by laser ablation decontamination from chromium-embedded cement, cement, alumina, and stainless steel surfaces were examined. The materials were aggregates of primary particles generated by laser ablation of plasma. More research is needed to identify the links between the provided materials' fundamental particles and aggregates. Regardless of laser wavelength, alumina generated the fewest particles at a set fluence. Annealing power has the greatest impact on aspect ratio, whereas micro structure width has the most effect on MRR. Analysis revealed that contaminants of alumina, stainless steel, and chromium were highly segregated into distinct areas of the aerosol's particle size distribution.

52. Dissimilar laser welding of a CoCrFeMnNi high entropy alloy to 316 stainless steel

J.P. Oliveira a, Jiajia Shen a, Z. Zeng b, Jeong Min Park d, Yeon Taek Choi d, N. Schell c, E. Maawad c, N. Zhou e, Hyoung Seop Kim d

aUNIDEMI, Department of Mechanical and Industrial Engineering, NOVA School of Science and Technology, Universidade NOVA de Lisboa, Caparica 2829-516, Portugal

bSchool of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Sichuan 611731, China

cInstitute of Materials Physics, Helmholtz-Zentrum Hereon, Max-Planck-Str. 1, Geesthacht D-21502, Germany

dGraduate Institute of Ferrous Technology, POSTECH (Pohang University of Science and Technology), Pohang 790-794, South Korea

eCentre of Advanced Materials Joining, Department of Mechanical & Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada

Scripta Materiallia (ELSEVIER) IF : 5.3 (2023) 

High-entropy alloys (HEAs) comprise a relatively recent class of metallic materials which possess remarkable thermophysical properties. The CoCrFeMnNi alloy presents good weldability, although most of the research on this topic has been focused on similar welding. Dissimilar welding of high entropy alloys is yet scarce. In this work, sheets of a cold-rolled equiatomic CoCrFeMnNi high entropy alloy and commercially available 316 stainless steel were used as the base materials. Pulsed laser welding along the joining interface was performed with a peak pulse of 2.25 kW, which had a duration of 10 ms and a total energy of 17.9 J. After welding, dissimilar laser welding of a rolled CoCrFeMnNi HEAs to 316 stainless was performed. Detailed microstructure characterization by means of electron microscopy, synchrotron X-ray diffraction, aided by mechanical property analysis, and thermodynamic calculations were used to understand and rationalize the microstructure evolution due to the weld thermal cycle and its impact on the joint performance. The fusion zone microstructure was composed of a single FCC structure. The microhardness increase regarding the as-cast base materials was observed. Large columnar grains developed in this region which ultimately will impact the joint mechanical performance. The welded joints presented a tensile strength of 450 MPa and elongation of 5%, showcasing the potential application of these dissimilar laser-welded joints for structural applications. 

51. Laser beam welding of CoCrFeNiMn-type high entropy alloy produced by self-propagating high-temperature syntheses 

Nikolai Kashaev 1, Volker Ventzke 1, Nikita Stepanov 2, Dmitry Shaysultanov 2, Vladimir Sanin 3, Sergey Zherebtsov 2

1Institute of Materials Research, Materials Mechanics, Department of Joining and Assessment, Helmholtz-Zentrum Geesthacht, Max-Planck-Str.1, 21502, Geesthacht, Germany

2Laboratory of Bulk Nanostructured Materials, Belgorod State University, Pobeda 85, Belgorod, 308015, Russia

3Merzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Academician Osipyan Str., 8, Chernogolovka, Moscow Region, 142432, Russia

Intermetallics (ELSEVIER) IF : 4.3 (2023) 

High-entropy alloys (HEAs) have recently emerged as a new class of advanced metallic materials with various applications. One promising class of HEAs is FCC-structured Co-Cr-Fe-Ni-Mn system alloys. Although the composition-structure properties relations of the Co-Cr-Fe-Ni-Mn system alloys are under investigation now, many aspects of their behavior have not received significant attention yet. Furthermore, not much information on welding HEAs is available. Recently, laser-based processes were only investigated for the cladding of HEAs. However, it is not clear whether HEAs can be successfully laser beam welded. Therefore, the effect of fiber laser beam welding on the structure and hardness of the CoCrFeNiMn-type HEA was reported. They performed the experiments using an 8.0 kW fiber laser and set the laser power to 2.0 kW and the scanning speed ranging from 3.0 m/min to 6.0 m/min. After that, they used the SEM/EDX, EBSD, TEM, and Vikers hardness testing machine. As a result, the difference in microstructure and grain orientation distribution between the base material, heat-affected zone, and fusion zone were not significant. An increased density of defects in the FCC matrix in the heat-affected zone as well as in the fusion zone in comparison to the base materials. Furthermore, the formation of the B2 precipitates after welding was found to be in reasonable agreement with the equilibrium phase diagram of the alloy produced. The microhardness measurements have revealed a significant increase in the microhardness from 153 HV in the base material to 208 HV in the fusion zone. The increase in the microhardness was attributed to the precipitation of the nanoscale B2 particles. 

50. Development of Concrete Building Cutting Technology Using HIgh-Power Laser

S. GOYA a, H. MORI b, T. OKUDA b , Y. FUJIYA c, N. SHIMONABE d, T. AKABA e

a)Research Manager, Manufacturing Technology Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd. 

b)Manufacturing Technology Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd. 

c)Senior Manager, Manufacturing Technology Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd. 

d)Chief Staff Manager, Nuclear Plant Component Designing Department, Nuclear Energy Systems, Mitsubishi Heavy Industries, Ltd. 

e)Manager, Research & Development Department, Nuclear Plant Service Engineering Co., Ltd. 

With the increasing power and better quality of laser oscillators, laser processing, which has not been applied to thick concrete, has been increasingly used in recent years. In this report, we describe laser cutting of thick concrete columns (with a maximum thickness of 1200 mm) by using high-power fiber laser of over 20 kW and an ultra-long focus optical system, aiming at establishing a remote demolition technology for nuclear plant buildings that are high radiation areas. This report also describes a new beam laser damper system using water that was developed as a technology for receiving the high-power laser beam passing through a cutting object, which has been an issue in high-power laser processing. 

49. Surface ablation efficiency and quality of fs lasers in single-pulse mode, fs lasers in burst mode, and ns lasers

M. Domke a, V. Matylitsky b, S. Stroj a 

a)Josef Ressel Center for Material Processing with Ultrashort Pulsed Lasers, Research, Center for Microtechnology, Vorarlberg University of Applied Sciences, Hochschulstr. 1, Dornbirn 6850, Austria 

b)Spectra-Physics, Feldgut 9, Rankweil 6830, Austria 

In recent years, the burst-mode caught a lot of attention in the field of ultrashort-pulse laser micro machining. One of the major issues is the influence of the burst pulse number and frequency on ablation efficiency and quality. A recent publication reported of a significant increase in ablation efficiency when processing with ≥25 burst pulses at ≥100 MHz burst frequencies. This raises the question of whether processing with such high pulse densities can be attributed to non-thermal ablation, or whether a quasi-nanosecond laser ablation behavior is achieved. To answer this question, we determined ablation efficiencies as function of fluence for silicon, stainless steel, and copper and compared the ablation quality at the optimal fluence using the following laser systems: femtosecond laser operated in single-pulse mode, fs laser operated in 28-pulse-burst mode with a burst pulse frequency of 148 MHz, and a nanosecond laser with a pulse duration of 175 ns, which is identical with the temporal length of the burst pulse train. The comparison showed that the burst mode used produces similar surface morphologies and melt burrs as the nanosecond laser, but at about 2/3 of its efficiency. 

48. Ultra vibration assisted laser (UVAL) treatment of copper for superhydrophobicity

Menglei Zhao a, Zeng Yang a, Jingnan Zhao a b, Pranav Shrotriya a b c, Yan Wang a b, Yuanchen Cui d, Zhiquan Guo a b 

a)Tianjin University of Science and Technology, Tianjin, China

b)Tianjin Key Laboratory of Integrated Design and On-line Monitoring for Light Industry & Food Machinery and Equipment, Tianjin, China

c)Iowa State University, Department of Mechanical Engineering, Ames, USA

d)U. S. Polyco, Ennis, USA

In this paper, a hybrid ultrasonic vibration assisted laser (UVAL) prepared copper surface of super-hydrophobic was reported. After UVAL treatment, the water contact angle (WCA) of copper surface to 3 μL water was 157.4°and the water slip angle (WSA) was less than 10°. The wettability, microstructure, chemical composition and durability of copper surface were measured by contact angle measuring instrument, field emission scanning electron microscopy (FESEM), surface predatory X-ray diffraction (XRD) and three-dimensional morphology. The results revealed that after UVAL treatment, the microcoral-like structure and nano-grass structure were formed on the surface of the sample, which were similar to the surface of lotus leaf. Ultrasonic vibration combined with laser treatment can accelerate the adsorption of airborne hydrocarbon contaminations on the surface of micro and nanostructures, and reduce the surface energy of copper particles on the surface. This study provides a fast, convenient and effective method for the rapid preparation of stable superhydrophobic copper surface. 

47. Development and testing of a laser-based decontamination system

A. Anthofer*, W. Lipopmann and A. Hurtado

Chari of Hydrogen and Nuclear Engineering, Institute of Power Engineering, Technische Universitaet Dresden, Germany

Decontamination of radioactive concrete surfaces may be necessary during operation or decommissioning of nuclear power plants. Usually only the upper layers of the concrete structure are contaminated and are removed using labor-intensive mechanical milling processes. Production of a large amount of dust, which can lead to secondary contamination, is inherent to these processes. Improvements in high-energy laser technology have now made it possible for laser radiation to be used in decontamination technologies for the removal of concrete layers. A decontamination unit comprising a diode laser with a beam power of 10 kW in continuous wave (CW) mode in combination with an autonomous manipulator was developed for use in nuclear plants. The laser beam melts the concrete surface to a depth of approximately 5 mm. Compressed air jets then detach the molten layer from the concrete surface and convey it to a suction system, with which it is transported to a collection container. Most of the radionuclides are trapped in the solidifying melt particles, which form an extremely stable effluent well suited to long-term storage. A relatively small amount of dust is generated in the process. Because there is no backlash during energy transfer, the laser device carrier can be designed to be lightweight and flexible. A specially developed manipulator that can move freely along walls and ceilings by means of suction plates is used for the carrier unit. This results in short setup times for preparing for use of the device and minimal personnel exposure to the radiation. Experiments were conducted on a concrete wall to demonstrate the functionality of the overall system in realistic conditions. An optimal ablation rate of 2.16 m2 /h at an ablation depth of 1–5 mm was achieved. Today’s commercially available diode lasers with powers higher than 50 kW enable ablation rates of 410 m2 /h to be achieved and hence make these laser-based systems competitive alternatives to mechanical systems.

46. A laboratory study about laser perforation of concrete for application in oil and gas wells

H. Kariminezhad1) , H. Amani2) and M. Moosapoor1)

1)Department of Physics, Babol University of Technology, Babol, Iran

2)Faculty of Chemical Engineering, Babol University of Technology, Babol, Iran

Laser perforation is the application of light to make a flow path between wellbore regions through the casing wall and cement layer all the way to reservoir production zone. Due to significant losses of laser power at long distances, introducing a novel method in order to facilitate laser perforation in oil and gas reservoirs is necessary. This paper aims to study on concrete perforation using a continuous 240 W/cm2 CO2 laser. In this research, the effect of water on the parameters of laser perforation such as rate of perforation (ROP), specific energy (SE) and dominant mechanisms was investigated. For this, two groups of concrete samples (dry and wet) were illuminated at 2, 6, 15, 30 and 60 s by the laser. Our results showed evaporation was main mechanism for dry samples at exposure times above 15 s, while spallation was the dominant mechanism for the wet samples at all exposure times. ROP and SE were significantly increased and decreased in the presence of moisture, respectively. Maximum ROPs obtained 2.26 mm/s and 0.45 mm/s for wet and dry samples, respectively. Also, minimum of SEs for wet and dry samples obtained 1.05 J/mm3 and 4.3 J/mm3, respectively. Finally, our experimental results were justified using a simplified heat conduction model. All these characteristics demonstrate presence of water in concrete possesses an important role to improve rate of laser perforation. Therefore, the results of this research could significantly reduce time and cost of laser perforation for application of oil recovery. 

45. Using a High-Power Fibre Laser to Cut Concrete

K. Nagai1) and K. Shimizu1)

1)Department of Architecture and Architectural Engineering, College of Industrial Technology, Nihon University, Japan

Concrete cutting at construction sites causes problems such as noise, vibration, and dust. In particular, during the demolition and renovation work on buildings in urban areas, protection against noise, vibration, dust, etc., is needed. Concrete cutting using a CO2 laser was investigated 20 years ago. However, this method had never used because the equipment is difficult to carry. In this study, we used a portable fibre laser, which is convenient to carry. Two types of concretes with different strengths were prepared for the experiment. High-strength concrete has never been used in similar research before. High-strength concrete is just only used for skyscrapers because of its high quality and cost. Furthermore, it has already been used for skyscrapers in Japan. It is for this reason that we chose to use it in this study. Irradiation measurements were conducted under various conditions using laser powers of 6 and 9 kW. It was confirmed that the cutting effectiveness of CO2 and fibre las ers was approximately identical for concretes with a thickness of 200 mm. Furthermore, the cutting effectiveness for the two concretes with different densities was almost the same. However, the situation after cutting was different because the vitrification of the cutting and glass formation progressed in low-density concrete and an explosion phenomenon occurred in high-density concrete, simultaneously. This study suggests that laser concrete cutting can be used as a solution when noise and dust are major problems. 

44. Laser weldability of cast and rolled high-entropy alloys for cryogenic applications

H. Nam1), C. Park1), J. Moon3), Y. Na2), H. Kim3), and N. Kang1)

1)Department of Materials Science and Engineering, Pusan National University, Republic of Korea

2)Titanium Department, Korea Institute of Materials Science, Republic of Korea

3)Department of Materials Science and Engineering, Pusan UniversityNational University, Republic of Korea

Laser similar welding of cast and rolled high-entropy alloys (HEAs) was performed using the cantor system (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2). As the welding velocity was increased from 6 to 10 m min−1, the shrinkage voids, primary dendrite arm spacing, and dendrite packet size decreased, thus improving the mechanical properties of the cast and rolled HEA welds. The cast HEA welds showed tensile properties comparable to those of the base metal (BM). In all the specimens fracture occurred near the heat-affected zone and BM at 298 K. However, the rolled HEA welds showed lower tensile strength than the BM, and fracture occurred in the weld metal (WM). This can be attributed to the larger dendrite packet size of the WM than the grain size of the BM. In addition, the tensile properties of the specimens at the cryogenic temperature were superior to those observed at 298 K, regardless of the cast and rolled HEA welds. This is because the formation of deformation twins and dislocations was predominant at 77 K. Therefore, the laser similar welds of cast and rolled HEAs are suitable for cryogenic applications. 

43. Microstructure and properties of Laser Surface Remelting AlCoCrFeNi2.1 HighEntropy Alloy

J. Chen1), J. Zhang1), K. Li2), D. Zhuang2), Q. Zang3), H. Chen3), Y. Lu4), B. Xu4) and Y. Zhang1)

1)School of metallurgy and materials engineering, Jiangsu University of Science and Technology, China

2)School of materials science and technology, Jiangsu University, China

3)School of materials science and technology, Jiangsu University of Science and Technology, China

4)Suzhou institute of technology, Jiangsu University of Science and Technology

In this study, laser surface remelting of an AlCoCrFeNi2.1 high-entropy alloy was performed using a Yb:YAG laser. The effects of laser surface remelting on the phase structure, microstructure, Vickers hardness, frictional wear properties, and corrosion resistance of the high-entropy alloy were investigated. The remelted layer of the AlCoCrFeNi2.1 high-entropy alloy was produced by remelting at 750 W laser power and formed a good metallurgical bond with the substrate. The X-ray diffraction results showed that the 750 W remelted layer consisted of face-centered cubic and body-centered cubic phases, which were consistent with the phases of the as-cast AlCoCrFeNi2.1 high-entropy alloy, and a new phase was not generated within the remelted layer. Laser surface remelting is very effective in refining the lamellar structure, and the 750 W remelted layer shows a finer lamellar structure compared to the matrix. The surface hardness and wear resistance of the AlCoCrFeNi2.1 high-entropy alloy were substantially improved after laser surface remelting. In a 3.5 wt.% NaCl solution, the laser-remelted surface had a larger self-corrosion potential and smaller self-corrosion current density, and the corrosion resistance was better than that of the as-cast high-entropy alloy. 

42. Colorizing metals with femtosecond laser pulses

A. Y. Vorobyev1) and  C. Guo1)

1)The institute of optics, University of Rochester, USA

This research team has demonstrated, visually and through spectral measurements, the creation of color metals with femtosecond laser surface structuring technique. We show that our technique essentially provides a controllable modification of optical properties of metals from UV to terahertz via surface structuring on the nano-, micro-, and submillimeter-length scales. The size of the optically modified metal surface area can be as small as a tightly focused laser spot, i.e., down to about 10 m, or as large as needed when a scanning laser beam is used. Given the additional advantages of laser processing such as low contamination and the capability to process complicated shapes, the color metals created in this work have tremendous potential in various technological applications. 

41. Effect of silica fume content in concrete blocks on laser-induced explosive spalling behavior 

Seong Y. Oh1), Gwon Lim1), Sungmo Nam1), Byung-Seon Choi1)

1)Korea Atomic Energy Research Institute

The experimental study is conducted to investigate the effect of silica fume mixed in concrete blocks on laser-induced explosion behavior. We use a 5 kW fiber laser as a thermal source to induce explosive spalling on a concrete surface blended with and without silica fume. An analytical approach based on the difference in the removal rate and thermal behavior is used to determine the effect of silica fume on laser-induced explosive spalling. A scanner is employed to calculate the laser-scabbled volume of the concrete surface to derive the removal rate. The removal rate of the concrete mixed with silica fume is higher than that of without silica fume. Thermal images acquired while scabbling is used to qualitatively analyze the thermal response of laser-induced explosive spalling on the concrete surface. At the early stage of laser heating, an uneven spatial distribution of surface temperature appears on the concrete, including silica fume, because of frequent explosive spalling within a small area. By contrast, in laser-heated concrete without silica fume, the spalling frequency is relatively lower, and a larger area is removed via one explosive spalling event owing to its high porosity. 

17. Laser decontamination of epoxy painted concrete surfaces in nuclear plants

원전 내 에폭시 도색 콘크리트 표면의 레이저 제염

A. Anthofer, W. Lippmann, A. Hurtado

Laser technology offers an efficient decontamination of surfaces contaminated by polychlorinated biphenyls (PCB) by precise application of highly focused laser beam power. In the context of nuclear decommissioning all walls and floors of a reactor building have to be cleaned from chemical-toxic substances. State of the art is a manual and mechanic ablation and a subsequent treatment in a hazardous waste incinerator. In this study, alternatively, a laser-based system exhibiting, decontamination rates of up to 6.4 m^2/h has been operated using a 10-kW diode laser in continuous wave (CW)mode with a spot size of 45 X 10 mm^2 and a wavelength of 980–1030 nm. The system allows a rapid heating of the surfaces up to temperatures of more than 1000 celsius degree leading to ablation and thermal decomposition of PCB  in one process step. Thermal quenching prevents formation of polychlorinated dioxines (PCDD) and polychlorinate furans (PCDF) in the flue gas. Additionally, an in situ measurement system based on laser induced fluorescence (LIF) is developed to monitor the thermal decomposition of PCB. Forinitial experiments samples covered with epoxy paint were used to evaluate the process and to carry out finite element based simulations. In this paper, experimental results of ablation tests by laser irradiation of epoxy painted concrete are presented and discussed.

16. Ultra-high power (100kW) fiber laser welding of steel

철의 초-고출력 (100kW) 파이버 레이저 용접

YOUSUKE KAWAHITO, HONGZE WANG, SEIJI KATAYAMA, AND DAICHI SUMIMORI

    A 100 kW fiber laser was first used to weld steel. Speeds at the range between 0.3 and 5.0 m/min were tested, and the maximum weld bead depth of 70 mm was achieved by single pass welding. Solidification cracking and porosity occurred when the welding speed was lower than 0.5 m/min, while undercut appeared when the welding speed was higher than 3.0 m/min. Both the ratio of depth to width and the cross section area of the weld bead had a positively linear relationship with the welding speed. A high speed camera was used to observe the characteristics of the keyhole and molten pool. The average number of spatters increased with the welding speed, while the keyhole diameter and the length of the molten pool in front of the keyhole decreased with the welding speed. This Letter validates the application potential of a 100 kW ultra high power fiber laser in manufacturing, e.g., welding, cutting, and additive manufacturing.

15. Studies on enhanced thermally stable high strength concrete incorporating silica nanoparticles

실리카 나노입자가 함유된 열안전성이 향상된 고강도 콘크리트에 관한 연구

R. Kumar, S. Singh*, L.P. Singh

 The performance of silica nanoparticles incorporated high strength concrete (SNPs-HSC) has been evaluated under elevated temperature conditions by exposing up to 800  C, followed by cooling to ambient temperature before performing experiments. Time-temperature studies revealed that incorporation of silica nanoparticles (SNPs) in concrete mix delays the heat transfer by 11%, 18%, 22% and 15% at 200  C, 400  C, 600  C and 800  C respectively thereby, decreasing the rate of degradation as compared to the conventional high strength concrete (HSC). A reduction in weight loss was observed in SNPs- HSC specimens after exposure to 200  C, 600  C, and 800  C; whereas at 400  C the weight loss quantity was  3.5% higher than the control HSC specimens due to the evaporation of water from calcium silicate hydrate (C-S-H) gel. On exposure up to 400  C for 2 h, the compressive strength and split-tensile strength increased by 40% and 13% respectively, for SNPs-HSC specimens, whereas in control HSC specimen’s strength didn’t increase after 200  C. A higher residual compressive (7%) and split-tensile strength (8%) was found to be in SNPs-HSC specimens exposed to 800  C for 2 h as compared to the control HSC specimens. The stress-strain curves revealed that SNPs-HSC specimens exhibits brittle failure up to 600  C whereas in control HSC brittle failure was observed only up to 400  C. Microstructural studies performed on the samples taken from the core of the 400  C exposed SNPs-HSC revealed the formation of higher C-S-H content and lower amount of calcium hydroxide (CH) leading to their enhanced mechanical and thermal stability. 

14. Laser scabbling of mortars

모르타르의 레이저저 스케블링

B. Peach*, M. Petkovski*, J. Blackburn, D.L. Engelberg

Laser scabbling of concrete is the process by which the surface layer of concrete may be removed through the use of a low power density laser beam. Previous research has suggested that the driving force responsible for laser scabbling is developed within the mortar. The aim of this investigation was to establish the key parameters that influence laser scabbling of mortars. All scabbling tests were carried out using an IPG photonics YLS-5000 (5kW) Yb-fibre laser. the specimens were subjected to a static, continuous, diverging laser beam with a stand off distance of 340mm from the focal point which gave a nominal beam diameter of 50mm. Tests were conducted with the laser beam applied to a vertical concrete surface to avoid debris falling back onto the specimen during testing. The results show that the removal of free water from mortars prohibits scabbling, but resaturation allows mortar to scabble. A reduced permeability, either due to a reduction in the water/binder ratio or the use of 25% PFA replacement, enhances the scabbling. A higher fine aggregate content increases volume removal and fragment sizes during laser scabbling.

13. Laser cutting of aluminium-alumina metal matrix composite

알루미늄-알루미나 금속 메트릭스 복합체의 레이저 절단

S. Marimuthu, J. Dunleavey, Y. Liu, M. Antar, B. Smith

Laser cutting of monolithic materials like metals and alloys is well-established and is used extensively in various industries including aerospace, medical and automotive. However, laser cutting of anisotropic materials like metal matrix composites (MMC) is challenging due to the differences in the chemical and physical properties of the matrix and fibre reinforcement. This manuscript contains details and results of an investigation into laser cutting of 2mm thick aluminium metal matrix reinforced with aluminium oxide fibre (Al MMC). The laser cutting mechanism and the influence of laser cutting parameters on the quality of cuts were examined in detail. The experimental results demonstrated that the laser cutting mechanisms of fibre reinforced MMCs are vastly different from the mechanisms observed in laser cutting of monolithic metals and alloys. The Al2O3 fibres within the MMC are not vaporized but are removed along with the molten, low melting point matrix materials. A thin and uniform layer of Al2O3 was been deposited over the cut surface which can be advantageous for applications that involve moving gases or fluids, for example, aero-engine cooling holes.

12. Surface Cleaning of Metals Using Low Power Fiber Laser

저출력 fiber laser를 이용한 금속 표면 세정

E. KAYAHAN, L. CANDAN, M.ARAS and O. GUNDOGDU

Lasers are used in industry in a large variety of applications. These applications can mainly be divided into two categories: one specifically being materials processing. Material processing includes cutting, drilling, welding, etc., and generally involves the use of high-powered lasers. Laser applications such as rust/dye removal and surface cleaning are not yet very common for the industry. This paper reports experiments on industrial applications of a ytterbium fiber laser (1064 nm) with a maximum output power of 20 W, pulse duration of 200 ns and pulse repetition rate of 10-100 kHz. Furthermore, the laser beam was focused on the target through a 160 mm focal length F-T lens. Scanning speed and line spacing of laser are 3-100 mm/s and 1-100 um, respectively. Experimental studies showed that a low-power fiber laser could be used for a variety of applications such as surface cleaning of metals and rust-dye removal. Optimum laser parameters were also determined for these applications.

11. High-Power Fibre Laser Cleaning for Green Shipbuilding

 G. X. Chen, T. J. Kwee, K. P. Tan, Y. S. Choo and M. H. Hong

Blasting techniques in shipbuilding and ship repair have been developed for surface preparation of steel to a standard equivalent to SA2.5 as defined by ISO Standard 8501. The usage of consuma-bles, such as abrasive materials, air and water, constitutes a recurring cost in these processes. When blasting work is carried out in the open space, such as during a dry docking, abrasive blasting gen-erates a lot of dusts which in turn pollutes the environment with consequential social and economi-cal costs. Laser blasting or laser cleaning, which has not been introduced commercially in shipbuild-ing and ship repair, offers an alternative for green manufacturing and green repairs. Laser cleaning has significant advantages on these issues over the conventional blasting techniques. It is a well-controlled process with unique properties, such as precise treatment, high selectivity, and high flexi-bility. A cleaning technique using a high-power fibre laser is developed for the surface preparation of steel. Fibre laser has advantages of compact system, automation capability, and low maintenance cost. We report the laser cleaning results using a 500-W pulsed high-power fibre laser. The laser cleaning is able to meet the SA 2.5 requirements of blast cleaning as described in the International Organization for Standardization (ISO) standard 8501.

10. Microstructural analysis of interfacial transition zone (ITZ) and its impact on the compressive strength of lightweight concretes

Interfacial transition zone (ITZ)의 미세 구조 해석과 경량 콘크리트의 압축강도에 미치는 영향 

P. Vargas, Oscar Restrepo-Baena, Jorge I. Tobón

   Lock-in thermography and heat flow measurements with peltier sensor(TEC-1089-SV) was performed during fatigue crack growth testing. Moreover, elastic stress fields (E-Amplitude) as well as dissipated energies (D-Amplitude) can be determined. In case of thermographic measurements the specimens have to be painted to enhance the emissivity, but the thickness of the coating influences the results and therefore quantitative measurements are problematic. The heat flow measurements are easy to perform and provide quantitative results, but only integral values in an area given by the size of the peltier element can be achieved. In order to get comparable results the evaluation of the thermographic measurements were performed in the same area as the peltier measurements. In case of the mean temperature measured by thermography and the heat flow determined with the peltier sensor a good agreement was found. The measurement of elastic stresses with the peltier sensor is restricted to low loading frequencies due to the response characteristic of the sensor. For the measurement of dissipated energies the cooling of the specimen by heat conduction into the clamps and heat radiation has to be taken into account.

8. Investigation on rock breaking for sandstone with high power density laser beam

고출력 레이저 빔을 이용한 사암 암석 파괴에 대한 조사

Meiyan Li, Bin Han, Qi Zhang, Shiyi Zhang, Qingkun He

6. Experimental Investigation of Multi-mode Fiber Laser Cutting Cement Mortar

다중 모드 광섬유 절단 시멘트 모르타르의 실험적 연구

D. K. Lee, S. H. Pyo