The phase stability at intermediate-temperature and mechanical behavior of the dual-phase AlCoCr0.5FexNi2.5 high entropy alloys

The dual-phase AlCoCr0.5FexNi2.5 (x = 0.5, 1.5, 2.5 and 3.5) high-entropy alloys (HEAs) were prepared and annealed at 600 °C for 50 h to better understand the phase stability at intermediate-temperature and their mechanical behaviors. The results revealed that a FCC-to-BCC phase transformation was occurred during annealing. The defined thermodynamic parameters (Ω) and atomic size difference (δ) attempted to explain the phase stability of HEAs. The HEAs with higher Ω and lower δ tend to exhibit better thermal stability under the intermediate temperature. The mechanical properties mainly depended on the fractions of each phase. The increased fraction of BCC/B2 phase and the optimization of phase distribution in the Fex alloys were the major factors improving the mechanical properties. The deformation inconsistency of dual-phase structure brought back stress hardening, enhancing both strain hardening capability and uniform elongation of the alloys. The strength of AlCoCr0.5Fe2.5Ni2.5 alloy was obviously improved without losing the plasticity undergoing the long-term annealing, showing a promising potential for engineering material applied in intermediate-temperature environments.