A non-equiatomic Ni-Co-Fe medium-entropy alloy with excellent wear resistance and strength-ductility combination by adding Al

In this work, a series of Al-doped AlxNi0.6CoFe1.4 (x = 0, 0.1, 0.2 and 0.3) medium-entropy alloys (MEAs) were prepared to investigate the mechanical and wear performances. The results reveal that the phase structure of AlxNi0.6CoFe1.4 MEAs is composed of disordered body-centered cubic (BCC) phase with a minor amount of ordered BCC (B2) phase after addition of Al. The mechanical tests show that the micro-hardness, tensile strength and fracture elongation initially increase and then decrease with increasing Al content. Specifically, the Al0.2 alloy exhibits the optimum mechanical properties, with the highest micro-hardness of 732.7 ± 16.1 Hv, the maximum tensile strength of 1103.6 ± 20.5 MPa and the maximum fracture elongation of 13.6 ± 0.9%, respectively. In addition, all Al-doped AlxNi0.6CoFe1.4 alloys exhibit a higher wear resistance compared with the Al-free Ni0.6CoFe1.4 alloy at dry sliding. The underlying mechanisms for the Al effect on the mechnical properties and wear resistance of AlxNi0.6CoFe1.4 MEAs were uncovered.