4. Addressing Erosion-Corrosion Problems in Marine Components through Friction Stir Processing
Erosion-corrosion is a critical problem in marine components and has huge economic impact. In the current study, friction stir processing was utilized for significantly enhancing the erosion-corrosion resistance of SS316L steel which is widely used in several marine applications. The friction-stir processed material showed nearly five times higher resistance to erosion-corrosion compared to the unprocessed alloy. The unusual enhancement in erosion-corrosion resistance was attributed to surface strengthening through grain-size refinement and martensite phase formation. In addition, higher corrosion resistance due to stronger passivation also contributed towards superior performance of the processed alloy.
3. Friction Stir Processing of Stainless Steel for Enhancing its Performance in Bio-Implant Applications
Bio-implants are exposed to harsh environment of the body and degrade typically by wear and corrosion in the physiological environment resulting in Metallosis. Stainless steel is one of the most commonly used implant material because of its biocompatibility, excellent mechanical properties, and low cost. In the current work, the surface properties of austenitic stainless steel was significantly enhanced using friction stir processing with different cooling conditions. The processed samples showed exceptionally high resistance to localized and intergranular corrosion. In addition, superior wear resistance was seen in dry tests and in simulated body fluid, which was explained by stronger passivation and higher hardness to modulus ratio. Surface engineering strategies for enhancing the performance of stainless steels may reduce or eliminate the need for implant removal surgeries and the associated cost.
2. Activation Energy and High Temperature Oxidation Behavior of Multi-Principle Element Alloy
1. Microstructure and Wear Resistance of an Intermetallic-based Al0.25Ti0.75CoCrFeNi High entropy alloy
An Al0.25Ti0.75CoCrFeNi high entropy alloy (HEA), consisting of multiple principal elements, forms the uncommonly observed chi-phase, which is a large lattice parameter intermetallic phase based on the body centered cubic crystal structure, as the matrix phase and a L21 phase (ordered Huesler phase, X2YZ-type based on the face-centered cubic structure) as a major secondary phase. Additionally, a face centered cubic phase with a high density of nano-twins is also present in the microstructure as a third phase. The extremely high Vicker’s hardness of the matrix chi phase (1090Hv±14) and of the L21 phase (570±9 HV ) along with low sliding coefficient of friction (~0.3) and low wear rate (~1.2x10-5 mm3/N·m) makes this HEA a promising candidate for mechanical wear-resistant applications. The wear resistance of the alloy was calculated to be 66 TPa and the coefficient of friction was ~0.3.
3. Pathways for enhanced wear and corrosion resistance in bulk metallic glasses
Surface characteristics of two Zr-based bulk metallic glasses were evaluated in terms of their corrosion and wear behavior in as-cast and thermally relaxed states. Fully amorphous structure was retained with thermal relaxation below the glass transition. Wear tests showed the surface degradation behavior more sensitive to structural aspects, while potentiodynamic polarization and electrochemical impedance spectroscopy tests showed influence of both alloy composition and free volume. There was an increase in surface hardness and elastic modulus for both alloys after thermal relaxation. Nano-scratch tests showed significantly lower friction coefficient in the relaxed glasses as compared to as-cast state. This surface rejuvenation was explained based on annihilation of free volume.
2. Reciprocating Sliding Wear Behavior of High Entropy Alloys in Dry and Marine Environments
The reciprocating sliding wear behavior of two high entropy alloys, CoCrFeMnNi and Al0.1CoCrFeNi, was evaluated in dry and marine environments. Both the alloys showed better wear performance in marine atmosphere as compared to dry condition, indicating negative synergy of wear and corrosion. Al0.1CoCrFeNi was more wear resistant compared to CoCrFeMnNi. Accelerated electrochemical corrosion tests were carried out to quantify the effect of passive layer on marine wear behavior. Al0.1CoCrFeNi showed lower corrosion rate, higher pitting resistance and greater degree of passivation. A strong correlation was found between the electrochemical polarization resistance and wear resistance.
1. Friction Stir Additive Manufacturing of Titanium Alloys for High Performance Military Applications
Friction stir additive manufacture is a novel rapid manufacturing tool for producing near net shape products, in very short production time. The speed of manufacturing is one or two orders of magnitude faster than conventional manufacturing techniques.
Abstract on SBIR website: https://www.sbir.gov/sbirsearch/detail/871641
2. Alternate Additive Manufacturing to Produce and/or Join Nuclear Quality Components
FSAM processing nuclear quality additive structures has application in all advanced manufacturing in the sectors of defense, energy conversion, aerospace, automotive, consumer and generally industrial/commercial.
Abstract on SBIR website: https://www.sbir.gov/sbirsearch/detail/891789
1. Alternative Additive Manufacturing to Produce Fossil Energy Critical Systems
Utilized FSAM to optimize T/P 92-grade steel as welds and produced as 3D near/net shape parts with complete characterization for FE applications. In addition to FSAM producing wide varieties of 3D near/net shape parts and welds in 92-grade steel for FE applications, other steels can be FSAM produced for FE applications as well as other steel alloys and virtually any metal alloy for applications in general industry/ commercial , defense, aerospace, automotive and consumer industries.
Abstract on SBIR website: https://www.sbir.gov/sbirsearch/detail/891795
The dry sliding wear behavior and mechanisms in a bulk metallic glass composite, Ti48Zr20V12Cu5Be15, composed of in situ crystalline dendrites in an amorphous matrix, was studied in reciprocating mode against a WC counterface loaded at 5 N and 10 N. The composite showed higher wear rates but lower coefficient of friction compared to a monolithic fully amorphous glass. Nanomechanical characterization was done to map the hardness and modulus of the crystalline and amorphous constituents of the composite. Nano-scratch test was done on each phase to evaluate the coefficient of friction. The observed hardness values scale according to Archard’s relationship for sliding wear behavior. No tribolayer formation was seen for the composite in sharp contrast to that of the monolithic metallic glass.
Friction stir processing of bulk metallic glass: Bulk Metallic Glass (LM1B) was friction stir processed, in an attempt to identify the processing parameters where thermoplastic flow is possible. The is the first step towards joining BMGs using friction stir welding. The significance of this activity was the inability of glasses to be joined by any conventional technique, without oxide entrapment and consequent deterioration of properties. The friction stir processed samples were characterized using SEM, TEM, DSC, Hardness and Modulus, and Electrochemical behavior by potentiodynamic polarization and electrochemical impedance spectroscopy.