Microstructure and tensile properties of Co-free Fe4CrNi(AlTi)x high-entropy alloys

Abstract

According to parameters of atomic size difference (δ), valence electron concentration (VEC) and the cost effectiveness, a series of high Fe-content and Co-free Fe4CrNi(AlTi)x (x = 0.2, 0.6 and 1.0) high-entropy alloys (HEAs) were designed. Effects of the content of Al and Ti on the microstructure and tensile properties were investigated. It is found that the constituent phases change from the single face-centered cubic (FCC) phase to FCC + body-centered cubic (BCC) + L21 phases and BCC + L21 phases as the Al and Ti content increases from 0.2 to 0.6 and 1.0, respectively. With increasing the Al and Ti content, the strength increases but the tensile plasticity decreases. Specifically, Fe4CrNi(AlTi)0.6 exhibits a good combination of a high strength of 858 MPa and a large tensile plasticity of 12.8%. The excellent tensile properties of this alloy are attributed to the synergetic effects of a soft FCC phase and hard BCC/L21 phases, and moreover, the uniform distribution of high-density L21 nanoparticles in the BCC phase also benefits the tensile properties. In addition, the phase-evolution principles in the current HEAs and in many previously-reported HEAs are well discussed within the framework of δ and VEC parameters. These findings are believed to promote the development of low-cost HEAs with high performance for practical applications.