Advanced high-temperature oxidation protection: A study of Al20V20Cr20Nb(40−x)Mox RHEA coatings on Ti6Al4V by laser cladding

The titanium alloy Ti-6Al-4V faces severe oxidation resistance challenges under extremely harsh working conditions. Refractory high-entropy alloy (RHEA) coatings with the nominal composition of Al20V20Cr20Nb40−xMox (x = 10, 20, 30 at. %) were successfully synthesized on the surface of Ti-6Al-4V substrates via an innovative laser cladding technique. The dependence of the coatings’ oxidation resistance on the Mo content was systematically examined. The Mo30 coating exhibits the best oxidation resistance, and its oxidation process conforms to the parabolic law. With the increase in Mo content, the surface oxide changes from scaly to dense granular. The oxidation products of Mo10/Mo20 coating are mainly TiO2 and Al2O3, which have weak protection. However, Mo30 coating generates composite oxides such as CrNbO4 and Al2TiO5, which effectively improve the antioxidant performance. Mo effectively inhibits oxygen diffusion by promoting the formation of a dense Al2O3 layer and an insulating layer. The study emphasizes the key role of complex oxides and dense oxide layers in improving the high-temperature oxidation resistance of the alloy at 800 °C, providing insights into the oxidation behavior of RHEA coatings under extreme conditions.