Effect of annealing on microstructure and mechanical properties for as-sintered Co-free Al_1·8CrCuFeNi₂ high entropy alloy

In this paper, a low-cost and light weight Co-free Al_1·8CrCuFeNi₂ high entropy alloy (HEA) was prepared. The evolution of microstructure and mechanical properties after annealing was investigated. Gas atomization was used to synthesize spherical HEA powder. The SEM results showed that the powder exhibited high quality and uniform composition. Bulk HEA was prepared by hot pressed sintering. The microstructure of as-sintered HEA consisted of worm-like BCC, rod-like B2 and streaky FCC phases. The presence of twin grains was observed in as-sintered Al_1·8CrCuFeNi₂ HEA. After annealing at 600 °C for 8 h, there was a lot of FCC phase in the Al_1·8CrCuFeNi₂ HEA matrix. However, as the annealing temperature increased, the FCC phase gradually decreased, and the streaky BCC phase transformed into spherical BCC phase. There was no presence of FCC phase at 900 °C with the variation of annealing time. Meanwhile, the change of annealing time had inapparent effect on the size of BCC phase, proving the high temperature stability of BCC phase. The optimum annealing process for the sintered Co-free Al_1·8CrCuFeNi₂ HEA was holding at 700 °C for 8 h. After annealing at 700 °C for 8 h, a fracture strain of 30.93% was achieved, which was a 50% increase over the as-sintered alloy.