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 C-HEA 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.