Effect of phase transformation on densification kinetics and properties of spark plasma sintered Al0.7CoCrFeNi high-entropy alloy

Al0.7CoCrFeNi high-entropy alloy (HEA), as a promising material, has attracted growing interest. This study aimed to investigate the effect of phase transformation in non-equilibrium Al0.7CoCrFeNi HEA on its properties and densification kinetics during spark plasma sintering (SPS). We found that the BCC-to-FCC phase transformation causes a grain size reduction from 5.66 to 3.10 mu m, while decreases the Vickers hardness from 372.5 +/- 4 to 328.4 +/- 3 HV. The decreased Vickers hardness reduces the wear resistance with the volume wear rate increasing from 1.583 x 10(-4) to 2.108 x 10(-4) mm(3).N-1.m(-1). Besides, the BCC-to-FCC phase transformation improves the ductility from 2.5 +/- 0.4 to 8.4 +/- 0.3%. The further precipitation of a theta phase observed in the sample sintered at 1100 degrees C improves the ultimate tensile strength from 856.1 +/- 13 to 1053.7 +/- 8 MPa, although the ductility decreases from 8.4 +/- 0.3 to 7.3 +/- 0.3%. Interestingly, we also observed that the BCC-to-FCC phase transformation reduces densification kinetics, because it decreases the diffusion coefficient.