Microstructures and hardnesses of AlCoCr0.5FexNi2.5 high entropy alloys with equal valence electron concentration

A group of high entropy alloys (HEAs) in equal valence electron concentration (VEC), AlCoCr0.5FexNi2.5 (x = 0.5, 1.5, 2.5, 3.5), were melted and prepared. The microstructures and hardnesses were analyzed after homogenizing treatment. The results indicated that all of the equal-VEC HEAs consisted of FCC phase and BCC phase, their orientations obey Kurdjumov–Sachs relationship. This work also implied that the atomic size difference (Δr), like VEC, is an important parameter influencing the phase selection and worth considering in the HEA design. Fe is an FCC phase stabilizer for AlCoCr0.5FexNi2.5 HEAs and the ordered FCC phase (L12) gradually disappear with the Fe addition increased. The increasing FCC phase and the decreasing BCC phase resulted in the decreased hardness of HEAs.