Tailored microstructures and strengthening mechanisms in an additively manufactured dual-phase high-entropy alloy via selective laser melting

Abstract

Dual-phase high-entropy alloys (DP-HEAs) with excellent strength-ductility combinations have attracted scientific interests. In the present study, the microstructures of AlCrCuFeNi3.0 DP-HEA fabricated via selective laser melting (SLM) are rationally adjusted and controlled. The mechanisms engendering the hierarchical microstructures are revealed. It is found that the AlCrCuFeNi3.0 fabricated by SLM at the scanning speed of 400 mm s−1 falls into the eutectic coupled zone, and increasing the scanning speed will make this composition deviate away from the eutectic coupled zone due to the increased cooling rate. The enrichment of Cr and Fe solutes with large growth restriction values ahead of the solid/liquid interface can develop a constitutional supercooling zone, thus facilitating the heterogeneous nucleation and near-equiaxed grain formation. The synergy of the near-eutectic DP nano-structures and near-equiaxed grains instead of columnar ones effectively suppresses cracking for the as-built DP-HEA. During the tensile deformation, the intergranular back stress hardening similar to the grain-boundary strengthening is discovered. Meanwhile, the near-eutectic microstructures comprised of soft face-centered cubic and hard ordered body-centered cubic (B2) DP nano-structures lead to plastic strain incompatibility within grains, thus producing the intragranular back stress. The Cr-rich nano-precipitates inside the B2 phase are found to be sheared by dislocation gliding and can complement the back stress. Additionally, multiple strengthening mechanisms are physically evaluated, and the back stress strengthening contributes obviously to the high performances of the as-built DP-HEA.