Controlled thermal oxidation of AlCrYTiZr high-entropy alloy for enhanced corrosion resistance and mechanical properties

High-entropy alloy (HEA) coatings show great promise for corrosion protection of critical marine component surfaces but are limited by passive film degradation during long-term service in extreme marine environments. In this study, amorphous AlCrYTiZr HEA coatings are deposited on X70 steel by magnetron sputtering and then thermally oxidized at 400 °C for 2, 30, or 60 min to form AlCrYTiZrO_x (x = 31.7, 41.4, or 46.0) coatings. It is observed that extending the thermal oxidation time to 30 min resulted in the formation of a dense oxide layer (∼200 nm thick) on the coating surface, accompanied by oxygen slow diffusion into the coating interior. Furthermore, thermal oxidation enhances the adhesion between the coating and the substrate. The combined action of the surface oxide layer and amorphous coating structure effectively blocks the penetration of the external corrosive medium. As a result, AlCrYTiZrO_41.4 shows a self-corrosion current density of 2.7 × 10⁻⁹ A/cm² and hardness of 17.87 GPa. Compared to the as-deposited AlCrYTiZr HEA coating, the self-corrosion current density of the coating decreases by a factor of 14, while the hardness increases by 2.37 times. The results reveal a concise and efficient strategy for enhancing HEA coating performance, thereby expanding its potential for corrosion protection applications on X70 steel surfaces. © 2026 Elsevier B.V.