Achieving a crackless, abrasion- and corrosion-resistant oxide coating on Ti-Zr-Hf-Nb-Al-Y refractory high-entropy alloy through Y alloying and high-temperature fast oxidation

Abstract

High-temperature oxidation is a facile technique to fabricate a wear- and corrosion-resistant oxide coating for metals. However, TiZrHfNb-based refractory high-entropy alloys (RHEAs) are prone to suffer from surface cracking during high-temperature oxidation processes, which is a common outcome observed in the high-temperature oxidation behavior of titanium alloys. This study introduces a novel approach to mitigate high-temperature oxidation cracking in the TiZrHfNbAl_0.5 RHEA by leveraging the synergistic effects of Y-alloying and precise oxidation control. It's found that surface cracking observed in the TiZrHfNbAl_0.5 RHEA following oxidation at 1000 °C is primarily attributed to the formation of needle-like (ZrHf)O₂ within the oxide layer. By combining Y-doping and an oxidation treatment at 1000 °C for 8 min, the generation of (ZrHf)O₂ is effectively suppressed, while a dispersion Y-Al-rich oxides is promoted, thereby creating a pinning effect that results in the formation of a crack-free oxide coating. Consequently, the oxidized TiZrHfNbAl_0.5Y_0.1 RHEA exhibits a wear rate that is two orders of magnitude lower and a corrosion current density that is one order of magnitude lower than those of the Ti6Al4V (wt%) alloy. A systematic analysis is also carried out to elucidate the oxidation mechanism underpinning this exceptionally wear- and corrosion-resistant RHEA. The present work offers new possibilities for the industrial applications of RHEAs in abrasive and corrosive environments.