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One of the key goals of processing 316L stainless steel by powder metallurgy (PM) techniques is to achieve industrial-viable tensile properties without structural defects like poor densification, undesired phase transitions, and oxidation during high-temperature sintering. To address this, this study adopts high-pressure torsion to fabricate a fully dense structure at ambient temperature through cold consolidation. The samples fabricated by the present PM-based technique exhibits considerably enhanced tensile properties compared to counterparts processed by conventional PM techniques, with a remarkable yield strength of 1 GPa and total elongation of 46%. Additionally, the segregation of certain elements during subsequent annealing results in a unique microstructure with nano-scale sigma precipitates which induces dislocation pile-up, leading to improved yield strength and retarded dislocation motion. The results indicate that the present PM-based route is an applicable technique to achieve the strength-ductility synergy in 316L stainless steel. [ABSTRACT FROM AUTHOR]

This study investigated the effects of deformation-induced martensitic transformation (DIMT) on the stretchability and fracture behavior of thin sheets made from ferrous medium-entropy alloys (MEAs). Analyses of punch load-stroke curves from Erichsen tests revealed that DIMT occurred in the 60 at% Fe MEA, 64 at% Fe MEA, and 304 stainless steel (60Fe, 64Fe, and 304SS alloys, respectively). This DIMT affects necking onset, uniform elongation, and the Erichsen index (EI) under diverse stress conditions. DIMT plays a significant role in strain hardening and mechanical instability during uniaxial tests, enhancing strain hardening through martensite formation and also initiating necking due to non-uniform deformation. Particularly in 64Fe, DIMT-induced early necking resulted in reduced uniform elongation. On the other hand, biaxial Erichsen test results demonstrated further strain hardening due to martensite-induced strain accommodation, leading to enhanced resistance to deformation during biaxial loading. The distinctive shapes of punch load-stroke curves in biaxial tests, compared to stress-strain curves from uniaxial tensile tests, are a result of the interaction between DIMT and stretching directions, as well as its alloy-dependent phase stability. In 60Fe, transformed martensite contributed to strain hardening and delayed necking initiation, while extensive martensite transformation in 64Fe enhanced strain hardening further. This understanding of the complex correlation between DIMT, strain hardening, and mechanical instability holds potential for alloy optimization and developing processing strategies, applicable to automotive manufacturing and structural engineering industries. [ABSTRACT FROM AUTHOR]

This study investigated the effects of deformation-induced martensitic transformation (DIMT) on the stretchability and fracture behavior of thin sheets made from ferrous medium-entropy alloys (MEAs). Analyses of punch load-stroke curves from Erichsen tests revealed that DIMT occurred in the 60 at% Fe MEA, 64 at% Fe MEA, and 304 stainless steel (60Fe, 64Fe, and 304SS alloys, respectively). This DIMT affects necking onset, uniform elongation, and the Erichsen index (EI) under diverse stress conditions. DIMT plays a significant role in strain hardening and mechanical instability during uniaxial tests, enhancing strain hardening through martensite formation and also initiating necking due to non-uniform deformation. Particularly in 64Fe, DIMT-induced early necking resulted in reduced uniform elongation. On the other hand, biaxial Erichsen test results demonstrated further strain hardening due to martensite-induced strain accommodation, leading to enhanced resistance to deformation during biaxial loading. The distinctive shapes of punch load-stroke curves in biaxial tests, compared to stress-strain curves from uniaxial tensile tests, are a result of the interaction between DIMT and stretching directions, as well as its alloy-dependent phase stability. In 60Fe, transformed martensite contributed to strain hardening and delayed necking initiation, while extensive martensite transformation in 64Fe enhanced strain hardening further. This understanding of the complex correlation between DIMT, strain hardening, and mechanical instability holds potential for alloy optimization and developing processing strategies, applicable to automotive manufacturing and structural engineering industries. [ABSTRACT FROM AUTHOR]

Recent material design aims at fabricating heterogeneous structures to overcome the strength-ductility trade-off. A severe plastic deformation process is adopted to a multi-interstitial high-entropy alloy to form precipitate-rich and precipitate-lean domains. By this approach, the alloy achieved a yield strength of ∼1020 MPa with a tensile elongation of ∼34 %. [ABSTRACT FROM AUTHOR]

Metal additive manufacturing (MAM) offers an excellent capability for designing complex geometries with topology-optimized and near-net-shaped structures. The optimization-designed MAM parts with constrained volume require superior mechanical properties to broaden their utilization in the industry. However, the intrinsic defects generated during the building process deteriorate the mechanical functionality and limit utilization in various industrial applications. In this study, we propose a new strategy to reduce generated defects using ultrasonic nanocrystal surface modification (UNSM) on laser powder bed fusion (LPBF) processed 316L stainless steel. Subsurface pores and high surface roughness in MAM parts were significantly improved through the impact of UNSM treatment, and a gradient structure with mechanical incompatibility was developed. Consequently, the LPBF-processed samples after UNSM treatment show the excellent combination of strength and ductility, which is attributed to the high synergistic hardening from the gradient microstructure and the suppression of damage evolution by controlling built defects. • The 316L stainless steel was fabricated by laser powder bed fusion (LPBF). • The LPBF-processed samples were treated using ultrasonic nanocrystalline surface modification (UNSM). • The UNSM-affected surface showed a high dislocation density and grain refinement, contributing to high strength. • The UNSM treatment effectively controlled building defects intrinsic in LPBF, suppressing damage evolution. • The UNSM treatment improved the combination of strength and ductility in LPBF-processed parts. [ABSTRACT FROM AUTHOR]