Microstructure evolution and cracking behaviors of additively manufactured AlxCrCuFeNi2 high entropy alloys via selective laser melting

Abstract

Abstract A series of AlxCrCuFeNi2 (labeled Al0, Al0.5, Al0.75, Al1.0) high entropy alloys (HEAs) were additively manufactured via selective laser melting, with emphasis on the influence of Al content on the microstructure evolution and cracking behaviors. The corresponding cracking mechanisms were also revealed. With the increase of Al content, there exists a transition of crystalline structures from face-centered cubic (FCC) to FCC plus body-centered cubic (BCC)/ordered BCC (B2), accompanied by a columnar-to-equiaxed transition. Interestingly, a eutectic-like microstructure comprised of a lamellar/cellular FCC matrix and interdendritic B2 matrix embedded with spherical BCC nano-precipitates is extensively formed in both the Al0.75 and Al1.0 alloys. The FCC dendrites and BCC nano-precipitates are enriched with Fe and Cr, whereas the interdendritic B2 matrix is enriched with Al and Ni. With the increase of Al content, there exists a transition of cracking mechanisms from the intergranular hot cracking induced by coarse columnar FCC grains to the transgranular cold cracking resulted from the fracture of brittle BCC grains under the severe residual stress. This is related to the transition of primary solidified phases from FCC to BCC. The formation of equiaxed grains eliminates the hot cracking and the eutectic-like microstructure prevents the initiation and propagation of cold cracking. The synergy of these two factors accounts for the elimination of hot and cold cracks in the Al0.75 alloy.