Effect of Al addition and homogenization treatment on the magnetic properties of CoFeMnNi high-entropy alloy

The effect of Al addition to CoFeMnNi on the phase evolution and magnetic properties was studied for vacuum arc-melted AlxCoFeMnNi (x = 0, 0.3, 0.7, 1) alloys. These alloys were subsequently homogenized at 1050° C for 50 h and water quenched. The CoFeMnNi and Al0.3CoFeMnNi alloys showed single-phase FCC in as-cast and homogenized conditions. The Al0.7CoFeMnNi alloy showed BCC + FCC phases in as-cast condition, and the phase fraction of FCC phase increased upon homogenization. The AlCoFeMnNi alloy had B2 phase in as-cast condition and had BCC + FCC phases after homogenization. Scheil simulation was performed to predict the phase evolution during casting, and calculation of phase diagram (Calphad) approach was used to predict the phase evolution during homogenization. CoFeMnNi alloy was ferromagnetic in as-cast condition, whereas it exhibits spin or cluster glass behaviour after homogenization. The Al0.3CoFeMnNi alloy remained paramagnetic in both as-cast and homogenized condition. In Al0.7CoFeMnNi alloy, the saturation magnetization increased from 20 to 60 emu/g upon homogenization. In the as-cast alloys, AlCoFeMnNi had a maximum saturation magnetization of 126.2 emu/g, and upon homogenization, the saturation magnetization decreased to 94.3 emu/g due to the phase change associated with it. The BCC/B2 phase with equiatomic or near-equiatomic composition had a high saturation magnetization. The change in magnetic properties is correlated to the phase change associated with Al addition and homogenization.