Influence of Heat Treatment on the Microstructure and Mechanical Properties of FeCoNiCrMn High-Entropy Alloy Manufactured via Laser Powder Bed Fusion

Laser powder bed fusion (L-PBF), as one of the additive manufacturing (AM) or 3D printing techniques, has been widely used for the net-shape fabrication of high-entropy alloys (HEAs). However, microstructural defects are often present in the FeCoNiCrMn high-entropy alloy fabricated via L-PBF, which necessitate subsequent heat treatment for optimization. In this study, FeCoNiCrMn HEA samples were fabricated using L-PBF and subsequently annealed at different temperatures. The influence of heat treatment on the microstructure and mechanical properties was investigated. The results revealed that the cellular substructure remained stable at 650 °C, while at 1100 °C dislocation recovery and compositional homogenization occurred, leading to the dissolution of the cellular substructure. After annealing at 1200 °C, the elongation of the alloy increased by 82%, while the yield strength and ultimate tensile strength decreased by 37% and 10%, respectively, compared to the as-built state. The cellular substructure not only contributed to strength through dislocation strengthening but also acted as nucleation sites for subsequent twinning, resulting in improved work hardening capability. Annealing-induced grain growth and substructure elimination improved the capacity of coordinated plastic deformation, while weakening the contribution of grain rotation and twinning mechanisms.