Long-term oxidation resistance of a Ti65 alloy with Cr2AlC coating by magnetron sputtering

Abstract

In this study, novel high-quality Cr₂AlC coating was fabricated on Ti65 alloy substrate as its protective oxidation resistance coating. Isothermal oxidation tests were performed at 650 and 750 °C for up to 400 h in air. The results indicated that Ti65 alloy underwent severe oxidation at 750 °C, accompanied by the presence of the cracking and exfoliating of the oxide scale during oxidation. Compared to the bare Ti65 substrate, the coated samples revealed more excellent oxidation resistance, meeting the parabolic law with low oxidation rate constants of 8.70×10⁻¹³ kg²·m⁻⁴·s⁻¹ at 650 °C and 2.80×10⁻¹³ kg²·m⁻⁴·s⁻¹ at 750 °C. At the surface, Al preferentially oxidized to form the protective Al₂O₃ layer and synchronously Cr₇C₃ sublayer, retarding the inward diffusion of oxygen and presenting excellent oxidation resistance. Besides, at the coating/substrate interface, Al diffused from Cr₂AlC coating into the substrate to form an Al-rich layer in substrate adjacent to the coating/substrate interface. Due to the Al consumption, Cr-carbide and nitride, as well as TiN, were thereby formed at the interface reaction layer, which could act as a barrier for the interdiffusion process.