Embedded Files
The mechanism of phase transformation and structure-property correlation at different length scales with a special emphasis at the nanoscale regime. The pathway and mechanism of phase transformation is mainly probed through X-ray, electron microscopy, differential scanning calorimetry etc. Structure-property correlations is mostly addressed by instrumented indentation at various temperatures and conventional mechanical testing methods. Advanced materials and composites inclusive of but not limited to aperiodic and complex intermetallics structures, and amorphous and conventional crystalline phases are of special interest.
Non-equilibrium and metastable equilibrium processing through advanced manufacturing processes as relevant to the study of microstructure, thermal and phase stability, and interfaces are of special interest. The research mostly revolves around quasicrystals, intermetallics, high entropy alloys, nano-composites including periodic and aperiodic intermetallics reinforcement, modification of hypo-eutectic Al-Si alloys, Cu and Cu-based complex alloys.
Schematic Representation of Research Work Related to Dr. Yagnesh Shadangi
Synthesis and characterization of Al-based quasicrystals and quasicrystalline matrix composites
These materials are seldom used in the realm due to their inherent room-temperature brittleness. Therefore, our research activities are mostly focused on the enhancement of fracture toughness of these alloys either by nanostructuring or by incorporation of soft phases like Sn in the QC matrix. The incorporation of Sn has led to a significant enhancement in the fracture toughness by ~22% by inhibition of cracks by Sn particles homogenously distributed in the QC matrix.
The sequence of structural transformation, phase composition, thermal stability and hardness of mechanically milled IQC-Sn powder were studied in detail. The XRD result suggests the formation of nanostructured composites. The IQC phase co-existed with Al13Fe4 and B2-type Al (Cu, Fe) phase, in IQC-Sn nanocomposite powder subjected to MM for 40 h. The double diffraction was observed due to the layering of nanocrystalline B2 and IQC phase in the nanocomposite powder (see Figure).
The phases formed during MM transforms to stable IQC phase along with crystalline phases during subsequent annealing treatment as confirmed by XRD and nano-beam diffraction (NBD). The fine structural and microstructural details of IQC-Sn milled samples are shown in the Figure. The structural transformations occurring during MM have a remarkable effect on indentation hardness, which is in the range of ~ 4 to 7 GPa. The bulk composite prepared by SPS has shown significant enhancement in the compressive yield strength ~75% for IQC-20Sn. The fracture toughness of the IQC-10Sn hot pressed composite was found to increase by ~22%. The increase in the compressive yield strength and fracture toughness of these bulk composite was attributed to the inhibition of cracks by soft Sn particles homogeneously dispersed in the IQC matrix by milling and sintering.
High-strength Al matrix composites reinforced with quasicrystals and high entropy alloys
The quasicrystals (QC) and high entropy alloys (HEAs) can be used as good reinforcement in the metal matrix composites because of their metallic nature, giving rise to good and strong chemical bonding between the matrix and the reinforcement. It has been shown that the addition of Al-based QC particles and HEAs in Aluminium Matrix composites (AMCs) would improve the mechanical properties. It has also been demonstrated that the addition of the QC/ HEAs reinforcement can enhance the strength of pure Al by a factor of 2–2.5.
Fabrication of these Al-QC composites through spark plasma sintering (SPS) at different temperatures and pressure gives us insight into microstructural evolution by the formation of various phases during sintering and its interface with the Al-based matrix. For fabricating Al-QC composite without any significant fraction of ω-Al7Cu2Fe phase, efforts were also made to consolidate them through SPS at high-pressure moderate temperature. The structure, microstructure, and mechanical properties of Al-QC composites fabricated at high pressure and moderate temperature were studied systematically.
The SPSed Al-QC composite has appreciable mechanical properties due to interfacial strengthening. These composites showed a promising compressive strength of ~900 MPa with an appreciable ductility of ~10%.
The microstructural features and microhardness of Al–HEA composites were investigated through SEM and instrumented indentation technique. The Al–HEA composite fabricated by pressureless sintering has exhibited an appreciable increase in hardness due to the homogenous distribution of reinforcement and the transitional layer formation at the interface.
Design & development of high entropy alloys (HEAs)
The literature on HEAs initially suggested the formation of a single phase. However, a few recent articles suggested the formation of secondary phases at high temperatures. The investigation of alloying behavior, thermal stability, and mechanical properties in various classes of HEAs i.e. Low-density HEAs (LDHEAs), Refractory HEAs (RHEAs), and High entropy steels (HES). The detailed investigation of these HEAs has discerned excellent strength and hardness ~2000 MPa and ~8 GPa respectively.
Surface modification of structural materials using LSP and USSP
There are several processes of surface modification like shot peening, Laser shock peening (LSP), ultrasonic shot peening (USSP) etc. Among these LSP and USSP have been found to be quite effective in improving fatigue resistance of structural components. LSP and USSP are known to cause severe plastic deformation in the surface region and generate a much higher level of compressive stresses as compared to other processes of surface modification.
These techniques are very effective in generating a gradient nanostrucutred layer along with the increase in the compressive stress that led to the increase in the strength along with the excellent ductility.
Attempts were made to understand the surface modification of Interstitial Free (IF) steel, commercially pure Ti, INCONEL 718 (IN718) by LSP and USSP. These surface modification techniques led to an enormous rise in hardness and strength with almost similar ductility in comparison to the untreated ones. These nanostructured layers generated on the surface of IF steels and superalloys were found to be stable even at elevated temperatures. The thermal stability of the surface nanostructured layer in IN718 at elevated temperatures up to 650 °C is evident from the optical micrograph and the diffraction contrast images as discerned in Figure.
Page updated
Report abuse