Superior oxidation resistance and unique mechanism in the chemically complex L1₂-strengthened high-entropy alloy

Developing alloys with both excellent mechanical properties and oxidation resistance is rather challenging but important for the aerospace industry. In our previous work, we have developed a chemically complex L1₂-strengthened high-entropy alloy (HEA), which exhibits excellent mechanical properties at elevated temperatures. However, its oxidation behavior is still unclear under the effects of multiple principal elements. In the present work, the oxidation behaviors this HEA were studied between 700 and 900 °C in air condition. Despite a relatively high content of Ti, the designed HEA exhibits superior oxidation resistance and unique oxidation mechanisms. The results show that the designed alloy follows a parabolic oxidation film growth dynamic and exhibits low oxidation rates of 4.96 × 10⁻⁶, 3.30 × 10⁻⁴, and 4.42 × 10⁻³ mg²/cm⁻⁴h⁻¹ at 700, 800, and 900 °C, respectively. The superior oxidation resistance can be attributed to the formation of continuous dense multi-oxidation layers, such as Cr₂O₃, Al₂O₃, TiTaO₄, sandwich structure of CoCr₂O₄-Cr₂O₃-CoCr₂O₄ etc. The Ti⁴⁺ ion incorporating into Cr₂O₃ lattice facilitated the formation of protective Cr₂O₃ layer. The formation of TiTaO₄ layer and NiO₂ oxides decreased the oxygen solubility within the interface between the matrix and the transient oxide layer, thus promoted continuous alumina layer formation at high temperature of 900 °C. This work provides valuable guidance for understanding the oxidation behaviors of HEAs with multi-component elements.