Ultra-Low Temperature Mechanical Response of Laser Powder Bed Fusion–Processed C-Containing CoCrFeMnNi High-Entropy Alloy

This study examined the microstructure and tensile behavior, from room temperature to 4.2 K, of a carbon-containing CoCrFeMnNi high-entropy alloy (HEA) fabricated by laser powder bed fusion (LPBF). Microstructural analysis revealed that the LPBF-built HEA comprised a single face-centered cubic (FCC) phase and exhibited epitaxial grain growth along the build direction. Dislocation cell structures and Cr-rich carbides were also observed within the grains. Tensile testing demonstrated a monotonic increase in both yield strength and ultimate tensile strength with decreasing temperature, and the LPBF-fabricated HEA consistently exhibited higher strength than its wrought counterpart across the entire temperature range investigated. Deformation twins were identified in all tested specimens, with the twin fraction increasing markedly at 4.2 K. These findings suggest that the excellent mechanical performance of the LPBF-fabricated carbon-containing CoCrFeMnNi HEA under ultra-low-temperature conditions is attributable to the combined effects of process-inherent microstructural features and pronounced deformation twinning.