Exploring the oxidation behaviors of the Ti[sbnd]V[sbnd]Cr[sbnd]Mo high-entropy MAX at 800 °C for its self-lubricity

Given the unique nanolaminate structure, the MAX phase ceramics which are composed of alternatively stacked two-dimensional (2D) metal (M) carbides (X) and main group (A) atomic layers have shown promising properties at elevated temperatures. Recently, an excellent self-lubricating performance of a high-entropy (HE) (TiVCrMo)₃AlC₂ MAX is demonstrated at 800 °C in the air. However, the formation mechanism of a self-lubricative tribofilm is still waiting for clarified. In this work, the HE (TiVCrMo)₃AlC₂ MAX is synthesized and its oxidation behaviors are systematically evaluated at 800 °C in the air. A two-stage parabolic oxidation behavior is detected, which can be mainly ascribed to the volatilization of MoO₃ species coupled with the thickening of the compound oxide scale. Meanwhile, the HE composition results in chemically complex phases including Rutile and vacancy-ordered TiO species in the oxide scale, which contribute to a higher ion diffusion rate for mass transportation. Consequently, the continued volatilization of MoO₃ is beneficial for the enhanced lubricity and anti-wear performance of the (TiVCrMo)₃AlC₂ MAX at 800 °C.