Heat treatment induced microstructural evolution and strength enhancement of Al–Cr–Fe–Ni–V high-entropy alloy fabricated by laser powder bed fusion

Abstract

Herein, different heat treatment protocols are adopted to further improve the mechanical properties of the Al–Cr–Fe–Ni–V high-entropy alloy (HEA) fabricated by laser powder bed fusion (LPBF) additive manufacturing (AM). The initial LPBF-processed HEA rendered a combination of high strength (ultimate tensile strength (UTS) of 810.93 MPa) and ductility (fracture elongation (FE) of 35.43%), which could be attributed to the hierarchical microstructure with fine grains, cellular dislocation structure, and L12 nano-precipitation. When the annealing temperature is increased from 573 K to 1473 K, the cellular dislocation structure is disappeared, and both L12 and B2 phases are progressively precipitated in the FCC matrix. Simultaneously, the tensile strength dramatically increased at the expense of ductility reduced and LPBF-processed HEA demonstrated a high UTS of 1192.84 MPa and FE of 15.32% after annealing at 1173 K. The results reveal that precipitation strengthening plays a significant role in improving the mechanical properties of LPBF-processed HEAs during annealing. For instance, L12 and B2 precipitates hindered the dislocation movement and, in turn, enhanced the pinning force of boundary migration. Moreover, the highly coherent and low misfit FCC-L12 interfaces minimized the strain accumulation due to the dislocation shear and, thereby, prevented the crack initiation.