High temperature oxidation of titanium–silicon alloys

The paper describes the behaviour of two Ti–Si alloys, with nominal composition (in wt.%) TiSi2 and TiSi8, during high temperature oxidation in air. The alloys were exposed to temperatures in the range of 650–850 °C for up to 320 h. The oxidation kinetics as well as the composition and morphology of scales were investigated and compared with those of pure titanium. Silicon has a positive effect on the oxidation resistance. Parabolic regression of kinetics curves shows that, in contrast to pure Ti, the process which governs the oxidation of Ti–Si alloys does not change up to 850 °C. Furthermore, the distribution of Si in the scales is not uniform, most likely due to the diffusion of Ti towards the surface during oxidation. Coarse eutectic Ti5Si3 particles in the TiSi8 alloy play an important role in the oxidation process. They progressively release silicon into the scales, which may cause an increase in the oxidation resistance with time. Moreover, these particles may have contributed to the formation of cracks in the scales.