Selective laser melting of dual phase AlCrCuFeNix high entropy alloys: Formability, heterogeneous microstructures and deformation mechanisms

Preparing dual-phase high-entropy alloys (DP-HEAs) by selective laser melting (SLM) has never been achieved owing to high crack susceptibility induced by rapid solidification. Here we design and fabricate new face-centered cubic (FCC) and body-centered cubic (BCC) DP-HEAs based on BCC AlCrCuFeNi HEA using SLM. Results show that the addition of Ni facilitates the columnar-to-near-equiaxed transition and improves the formability of the as-built AlCrCuFeNix (2.0 <= x <= 3.0) HEAs. Especially, the as-built AlCrCuFeNi3.0 HEA exhibits modulated nano-sized lamellar or cellular dual-phase structures and possesses the best combination of ultimate tensile strength ( similar to 957 MPa) and ductility (similar to 14.3%). Post-deformation research reveals that the FCC phase is deformed through planar dislocation slip with {111} < 110 > slip systems, and stacking faults (SFs). In the ordered BCC (B2) phases, high densities of Cr-rich nano-precipitates make B2 phase severely distort during tension, thus triggering the formation of deformation nano-twins and SFs on {112} planes. Strain-activated B2-to-FCC phase transition occurs in the B2 phase. Moreover, serrated tensile flow is first discovered in DP-HEAs due to the continual initiation and propagation of twins in the B2 phase. The uncovered synergy of various deformation modes and the underlying back stress strengthening induced by heterogeneous microstructures contribute to the high ultimate tensile strength and good ductility of the as-built AlCrCuFeNi3.0 HEA.