Superior thermal stability and strength of additively manufactured CoCrFeMnNi high-entropy alloy via NbC decorated sub-micro dislocation cells

Abstract

Additively manufactured metallic alloys often exhibit mesoscale chemical-structural heterogeneity due to the inherent melting and solidification processes. The resulting metastable microstructural constituents, ranging from dislocation cells to non-equilibrium precipitates, significantly impact either the thermal stability in the subsequent heat treatment procedure or the load-bearing performance at elevated temperatures for the additively manufactured alloys. This study focuses on NbC-added CoCrFeMnNi high-entropy alloys (NbC-HEAs) that were prepared using laser beam powder bed fusion (PBF-LB) with ball-milled mixed powders (5 wt.% NbC nanoparticles). The results showed that PBF-LB HEAs contain sub-micro Mn/Ni-decorated dislocation cells, and the addition of NbC leads to additional Nb segregation at cellular boundaries. After an 800 °C heat treatment, the dislocation density gradually decreased, the cell size increased, and Mn/Ni segregation was reduced for PBF-LB HEAs. In contrast, PBF-LB NbC-HEAs demonstrated superior thermal stability due to the formation of NbC precipitates at cellular boundaries, resulting in exceptional yield strength.