Fabrication of Layered Cu-Fe-Cu Structure by Cold Consolidation of Powders using High-pressure Torsion

In this study, the layered structures of immiscible Fe and Cu metals were employed to investigate the interface evolution through solid-state mixing. The pure Fe and Cu powders were cold-consolidated by high-pressure torsion (HPT) to fabricate a layered Cu-Fe-Cu structure. The microstructural evolutions and flow of immiscible Fe and Cu metals were investigated following different iterations of HPT processing. The results indicate that the HPTprocessed sample following four iterations showed a sharp chemical boundary between the Fe and Cu layers. In addition, the Cu powders exhibited perfect consolidation through HPT processing. However, the Fe layer contained many microcracks. After 20 iterations of HPT, the shear strain generated by HPT produced interface instability, which caused the initial layered structure to disappear.22Nkc

Superior cryogenic tensile properties of ultrafine-grained CoCrNi medium-entropy alloy produced by high-pressure torsion and annealing

Ultrafine-grained materials with nanotwins are expected to produce a remarkable combination of strength and ductility. In the present study, ultrafine-grained CoCrNi medium-entropy alloy with nanotwins is fabricated by high-pressure torsion followed by annealing; and investigated for cryogenic tensile properties. The alloy exhibits superior cryogenic tensile properties with a tensile strength of similar to 2 GPa and tensile strain of similar to 27%. The cryogenic tensile strength of ultrafine-grained sample increased by 67% as compared to the cryogenic tensile strength of coarse-grained sample due to fine grain size, annealing nanotwins, residual dislocation density, and strong temperature dependence of yield strength. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.11Nsciescopu

TiC-reinforced CoCrFeMnNi composite processed by cold-consolidation and subsequent annealing

Nanostructured CoCrFeMnNi high-entropy alloy (HEA) reinforced with TiC nanoparticles was fabricated through cold-consolidation using high-pressure torsion followed by annealing. The microstructural and hardness evolutions of the HEA-TiC composite have been compared with the monolithic HEA sample (without TiC) fabricated by a similar route. The HEA-TiC composite with high densification of 99.5% and uniform distribution of TiC nanoparticles showed retarded grain growth due to the pinning effect and enhanced hardness compared to monolithic HEA. The HPT cold consolidation fabrication route can be utilized to produce various HEA-matrix composites.11Nsciescopu

Role of cellular structure on deformation twinning and hetero-deformation induced strengthening of laser powder-bed fusion processed CuSn alloy

© 2022 Elsevier B.V.The sub-grain cellular dislocation structure has been reported to be the primary reason for the enhanced mechanical properties in laser powder-bed fusion (LPBF) parts. In the current work, the contribution of the cellular dislocation structure to the yield strength of LPBF processed CuSn alloy is estimated to be ~45%. In addition, this work shows that the cellular dislocation structure significantly controls the deformation behavior of LPBF processed CuSn alloy by suppressing the formation of deformation twinning. Post-LPBF heat treatment with fully recrystallized microstructures devoid of cellular dislocation structure showed pronounced twinning activity. The reduced homogeneous slip length due to the fine dislocation cell structure ~600 nm and increased stacking fault energy due to the cellular Sn segregation significantly increased the activation energy for the nucleation and propagation of the partial dislocations and suppressed the deformation twinning in the as-built samples. Furthermore, the present work shows that cellular dislocation structure contributes significantly to the hetero-deformation induced strengthening, much higher than the heterogeneous grain structure in the LPBF samples.11Nsciescopu

Effect of Annealing on Microstructure and Tensile Behavior of CoCrNi Medium Entropy Alloy Processed by High-Pressure Torsion

Annealing of severely plastic deformed materials is expected to produce a good combination of strength and ductility, which has been widely demonstrated in conventional materials. In the present study, high-pressure torsion processed CoCrNi medium entropy alloy consisting of a single face-centered cubic (FCC) phase with a grain size of ~50 nm was subjected to different annealing conditions, and its effect on microstructure and mechanical behavior was investigated. The annealing of high-pressure torsion processed CoCrNi alloy exhibits partial recrystallization and near full recrystallization based on the annealing temperature and time. The samples annealed at 700 °C for 2 min exhibit very fine grain size, a high fraction of low angle grain boundaries, and high kernel average misorientation value, indicating partially recrystallized microstructure. The samples annealed for a longer duration (>2 min) exhibit relatively larger grain size, a low fraction of low angle grain boundaries, and low kernel average misorientation value, indicating nearly full recrystallized microstructure. The annealed samples with different microstructures significantly influence the uniform elongation, tensile strength, and work hardening rate. The sample annealed at 700 °C for 15 min exhibits a remarkable combination of tensile strength (~1090 MPa) and strain to failure (~41%)

Effect of heat treatment on microstructural heterogeneity and mechanical properties of 1%C-CoCrFeMnNi alloy fabricated by selective laser melting

In this study, we quantitatively investigated the effect of heat treatment on microstructural evolution and mechanical properties in the selective laser melting (SLM) processed 1%C-CoCrFeMnNi high-entropy alloy (C-HEA). The addition of carbon atoms resulted in a nano-sized Cr23C6 carbide phase in the SLM-processed C-HEA, significantly retarding the kinetics of recrystallization and grain growth during the annealing heat treatment. The volume fraction of the carbide in SLM-processed C-HEA increased from -1.7 vol% to -2.9 vol% after exposure to the annealing heat treatment in the temperature range of Cr-rich carbide formation. After annealing, the combination of ultimate tensile strength and uniform elongation is improved with enhanced strain hardening ability. The increased volume fraction of finely distributed nano-carbides at cell boundaries in the annealed CHEA can effectively generate high back stress by profuse geometrically necessary dislocations (GNDs) during plastic deformation. This work demonstrates that the heat treatment of the SLM-processed C-HEAs is an attractive method to enhance mechanical properties and the reliability of product quality used in high-tech applications. This work also provides theoretical support to beneficially control the microstructural heterogeneity in the SLM-processed alloys to obtain the desired performance in structural parts.11Nsciescopu

Ultrahigh high-strain-rate superplasticity in a nanostructured high-entropy alloy

Superplasticity describes a material's ability to sustain large plastic deformation in the form of a tensile elongation to over 400% of its original length, but is generally observed only at a low strain rate (similar to 10(-4)s(-1)), which results in long processing times that are economically undesirable for mass production. Superplasticity at high strain rates in excess of 10(-2)s(-1), required for viable industry-scale application, has usually only been achieved in low-strength aluminium and magnesium alloys. Here, we present a superplastic elongation to 2000% of the original length at a high strain rate of 5x10(-2)s(-1) in an Al-9(CoCrFeMnNi)(91) (at%) high-entropy alloy nanostructured using high-pressure torsion. The high-pressure torsion induced grain refinement in the multi-phase alloy combined with limited grain growth during hot plastic deformation enables high strain rate superplasticity through grain boundary sliding accommodated by dislocation activity.11Ysciescopu

Work hardening behavior of hot-rolled metastable Fe50Co25Ni10Al5Ti5Mo5 medium-entropy alloy: in situ neutron diffraction analysis

© 2022 The Author(s). Published by National Institute for Materials Science in partnership with Taylor & Francis Group.Metastability engineering is a strategy to enhance the strength and ductility of alloys via deliberately lowering phase stability and prompting deformation-induced martensitic transformation. The advantages of the strategy are widely exploited by ferrous medium-entropy alloys (MEAs) that exhibit phase transformation from metastable face-centered cubic (FCC) to hexagonal close-packed (HCP) or body-centered cubic (BCC) martensite and a significant increase in work hardening. Fe50Co25Ni10Al5Ti5Mo5 (at%) MEA is an example of such materials, which shows ~1.5 GPa of tensile strength assisted by exceptional work hardening from the deformation-induced BCC martensitic transformation. In this work, the martensitic transformation and its effect on the mechanical response of the MEA were studied by in situ neutron diffraction under tensile loading. Strain-induced BCC martensite started forming rapidly from the beginning of plastic deformation, reaching a phase fraction of ~100% when deformed to ~10% of true strain. Lattice strain and phase stress evolution indicate that stress was dynamically partitioned onto the newly formed BCC martensite, which is responsible for the work hardening response and high flow stress of the MEA. This work shows how great a role FCC to BCC martensitic transformation can play in enhancing the mechanical properties of ferrous MEAs.11Nsciescopu

2.3 GPa cryogenic strength through thermal-induced and deformation-induced body-centered cubic martensite in a novel ferrous medium entropy alloy

A novel non-equiatomic FeCoNiAlTiMo ferrous medium-entropy alloy (MEA) with ultra-high tensile strengths at 298 and 77 K is presented in this work. By subjecting the MEA to hot rolling without further heat treatment, a quasi-dual-phase microstructure consisting of retained face-centered cubic (FCC) and thermal body-centered cubic martensite (BCC) phases with a very high density of dislocations and precipitates of Mo-rich mu phase was created. The high dislocation density significantly accelerated deformation-induced martensitic transformation from the remaining metastable FCC to BCC and successfully increased strain hardening ability. The strain hardening ability was even higher at 77 K due to decreasing FCC phase stability at lower temperatures. The increased strain hardening ability led to an excellent balance of strength and ductility, with ultimate tensile strength/uniform elongation of similar to 1.5 GPa/similar to 15% at 298 K and similar to 2.3 GPa/similar to 11% at 77 K. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.11Nsciescopu