Effect of Al/Ni ratio on phase, microstructure and mechanical properties of the AlxCrFeMnNi2-x high entropy alloys

In this work, the as-cast AlxCrFeMnNi2-x (x = 0.3, 0.7, 1.0) high-entropy alloys (HEAs) were designed via the empirical criterion and equilibrium phase diagrams, and the effect of Al/Ni ratio on the microstructure and mechanical properties was investigated and discussed. An increase of Al/Ni ratio promotes the matrix phase transition from FCC to BCC phase, this mainly is attributed to the decrease of VEC. No matter it is in FCC- or BCC-dominant HEAs, the ordered B2 phase (rich-Al and Ni) always appears together with the BCC phase, but the morphology of which translates from spherical-shape to cubical-shape, and to the weave-like microstructure due to the increase of the lattice misfit constant epsilon. The alloy (x = 0.3) is composed of FCC matrix phase with a small amount of BCC and spherical B2 precipitates, which exhibits favorable total ductility (similar to 80 %), but low yield strength (similar to 304 MPa); An increase of Al/Ni ratio results in the increase of the yield strength, but the decrease of the ductility. The alloy (x = 0.7) consists of the BCC matrix phase with trimodal (r-p, c-p, and s-p) distribution of B2 precipitates, which exhibits the optimal mechanical properties with the yield strength (similar to 1158 MPa) and a relatively high total ductility (similar to 50 %). Further increase of Al/Ni ratio does not influence the strength considerably, but decreases the total ductility sharply. The alloy (x = 1.0) presents a yield strength (similar to 1119 MPa) close to that of the alloy (x = 0.7), while the ductility is very low (similar to 10 %). It is mainly attributed to the spinodal weave-like microstructure, which is prone to the initiation and propagation of cracks.