Ultra-high temperature oxidation resistant refractory high entropy alloys fabricated by laser melting deposition: Al concentration regulation and oxidation mechanism

Poor oxidation resistance is a critical factor limiting the application of metalllic materials at ultra-high temperature environments. In this contribution, Alx(CrMoTaTi)1−x (x = 0.05, 0.1, 0.15) refractory high entropy alloy (RHEA) system was fabricated by laser melting deposition. The as-deposited RHEA was composed of two body-centered-cubic phases (BCC1 and BCC2). It was found that the volume fraction of BCC2 was increased with increasing the Al concentration from 0.05 to 0.15 and, surprisingly Al0.15(CrMoTaTi)0.85 could thermally grow an external Al2O3 scale during oxidation in air at 1300 °C. The insights into the microstructure-based oxidation mechanism of the RHEA were illustrated.