Amorphous Alumina Films Efficiently Protect Ti6242S against Oxidation and Allow Operation above 600 °C

The protection of the titanium based Ti6242S alloy against oxidation at moderate temperature is investigated, through the application on its surface of a 300 nm thick, amorphous alumina film. The latter is processed by metalorganic chemical vapor deposition at 500 °C from dimethyl aluminum isopropoxide. Upon oxidation at 600 °C for 5000 h, an interfacial zone is created between the alloy and the external protective layer, composed of unaffected alumina. In these conditions, the mass gain per unit area is eight times lower than that of the bare alloy, while the hardness of the alloy remains unaffected, revealing negligible oxygen ingress attributed to the efficiency of the protective coating. Finally, alumina coated samples show negligible mass change after 80 one-hour thermal cycles between 50 °C and 600 °C, showing excellent coating adherence on the Ti alloy.