Design of refractory high entropy alloys for extreme environment by using CALPHAD

To predict the stable phase of high entropy alloys (HEAs) with complex compositions, a composition design for HEAs using a calculation phase diagram with a combination of valence electron concentration was proposed. In the present study, Ti1.25ZrHfNbCr2 was designed as a refractory HEA (RHEA) using the proposed method, and the predicted stable phases were in good agreement with those of the alloys fabricated through arc melting. Continuous and stable oxidation tests up to 1500 °C and at 1200 °C, respectively, was performed, which indicated that the rate of weight gain of Ti1.25ZrHfNbCr2 decreased compared to that of an equi-atomic RHEA (TiZrHfNbCr). Microstructural observations revealed that a uniform distribution of metal elements in both the oxidized and unoxidized areas was only observed in Ti1.25ZrHfNbCr2, which is an important design guideline for preventing the oxidation of HEAs.