Effects of Cr/Fe Ratio on Structural Evolution and Tensile Properties of the Fe75.7−xCrxNi15.1Al4.6Ti4.6 High‐Entropy Alloys

Abstract

According to the effect of valence electron concentration (VEC) on the phase evolution of high‐entropy alloys (HEAs), Fe75.7−xCrxNi15.1Al4.6Ti4.6 (at%, x = 17.1, 18.9, 20.6, 22.3, and 25.3) HEAs are designed. Effects of the Cr addition on the microstructure and tensile properties are investigated systemically. As the Cr/Fe ratio increases (i.e., decreasing VEC), there is a phase transition from face‐centered‐cubic (FCC) to body‐centered‐cubic (BCC) and Heusler‐type β′ ‐Ni2TiAl (L21). When x is between 17.1 and 22.3, the alloys, with the mixed structure of the FCC and BCC/L21 phases, behave like composites with a sharp increase in strength but reduced ductility. When x = 25.3, the alloy, with only BCC/L21 phases, becomes extremely brittle. Specifically, Fe56.8Cr18.9Ni15.1Al4.6Ti4.6 exhibits a good combination of a high strength of 1142 MPa and an elongation strain of 9.5%. The excellent tensile properties of this alloy are attributed to the synergetic effects of a soft FCC phase, a hard BCC phase, and the uniform distribution of high‐density L21 nanoparticles in BCC matrix. The phase‐evolution principle is delineated by parameters of the VEC and the atomic size difference (δ), and the strengthening mechanism is well discussed. These findings offer a guidance for the development of BCC/L21‐containing HEAs for practical applications.