Heterogeneous structure induced excellent mechanical and wear properties in Co-free FeCrAlNi medium-entropy alloys

Microstructure design and realization is an effective way to achieve strength-ductility synergy in high-entropy. In this work, two novel non-equiatomic Co-free low-cost medium-entropy alloys (MEAs), Fe30Cr30Al20Ni20 and Fe20Cr20Al30Ni30, were designed and prepared using an arc-melting method. Its phase constitution, microstructure, mechanical and wear properties, as well as the strengthening mechanisms were investigated. It showed that both the MEAs are composed of BCC and B2 phases, rich in Fe–Cr and Ni–Al, respectively. The microstructure analysis indicated that the two MEAs have heterogeneous structures containing high-density precipitates and two alternant dual-phase eutectic structures. Significantly, the two MEAs possess excellent mechanical properties, better than most FeCrAlNiCo-based and FeCrAlNi-based HEAs reported previously. In the two MEAs, Fe20Cr20Al30Ni30 exhibits more excellent comprehensive mechanical and wear properties, with the compressive yield strength of 1154.5 MPa, maximum strength of 3271 MPa, maximum strain of over 40% and wear rate of 0.989 × 10−5 mm3N−1m−1, attributed to the novel heterogeneous microstructure. These results showed that the Co-free low-cost MEAs could have great prospects in practical engineering applications.