Influence of silicon on high-temperature cyclic oxidation behaviour of titanium

The paper compares the high-temperature cyclic oxidation behaviour of TiSi2 and TiSi8 with that of pure titanium. One experimental cycle consisted of heating at a temperature of 850 °C or 1050 °C for 12 h, followed by rapid cooling to the room temperature. Each experiment comprised six cycles. The cyclic oxidation kinetics as well as the structure, properties and composition of scales were investigated. The experiments clearly proved the positive effect of silicon on the cyclic oxidation resistance of titanium. The influence of silicon was shown to be more pronounced at a lower temperature of the cyclic oxidation (850 °C). At a higher oxidation temperature (1050 °C), its influence was still evident but less significant. In contrast to the Ti-Si alloys oxidised at 850 °C, the scales formed after cyclic oxidation at 1050 °C were much more porous and cracked due to stresses induced upon rapid cooling. A higher fraction of coarse silicide particles in the case of the TiSi8 alloy resulted in an increased cracking and porosity of the scales. The structure of the scales formed after oxidation at 1050 °C was complex. The scales were composed of at least two sub-layers, one containing a negligible concentration of silicon and the other, inner one, containing an increased amount of silicon. The nitride layer occurring beneath the scales was thicker for the TiSi8 alloy, due to a higher fraction of the scale porosity.