High Temperature Oxidation Mechanism Of Ti₃SiC₂/SiC Composites

In this paper, Ti₃SiC₂/SiC composites containing different contents of SiC were fabricated with TiH₂, SiC and graphite powders by in situ synthesis under hot isostatic pressing (HIP), to provide new ideal for the application of Ti₃SiC₂. It is the highest 64% volume content with addition of SiC content in the end-product Phase. According to density tests results, the composites are high density, their relative density are beyond 99%. The research indicates that Ti₃SiC₂/SiC composites endowed excellent overall performance especially high temperature oxidation resistance for high temperature structural materials。Phase structure, composition, grain size and grain morphology of Ti₃SiC₂ ceramics and Ti₃SiC₂/SiC composites were investigated by X-ray diffraction and optical microscope. The testing results indicate that the major phases of Ti₃SiC₂ ceramics are Ti₃SiC₂ and a few TiC phases, Ti₃SiC₂/SiC composites are Ti₃SiC₂, SiC and a few TiC phases.The high temperature oxidation behaviors of Ti₃SiC₂/SiC composites with different temperatures had been by thermogravimetry tests(TG) through simulating air atmospheres. According to the studies of the cures of weight grain of the materials, the oxidation resistance of Ti₃SiC₂ is to be excellent at temperatures below 1100℃. But the property is no longer excellence above 1100℃. It is concluded that the high temperature oxidation dynamics curve of the Ti₃SiC₂/SiC composites obey a parabolic oxidized law or parabolic-linear oxidized law. While temperature rising, the oxidation parabolic rate constantly increased. Compared the oxidation behaviors of Ti₃SiC₂/SiC composites with different contents of SiC oxidized at 1100℃for 40h, the growth of the oxide scale on Ti₃SiC₂/SiC composites per area decreases with increasing in the contents of SiC. It is demonstrated that the oxidation resistance property of all Ti₃SiC₂/SiC composites are better than that of pure Ti₃SiC₂ ceramics.Ti₃SiC₂/7SiC composites (64vol.%) indicate different oxidation law at high temperatures(1400℃) for long time. The weight gain is lower, the oxidation parabolic rate constantly decrease about one order compared to that at 1200℃for long time. The oxidation resistance of the composites at 1400℃is better than that at 1200℃for long time. Addition of SiC(64vol.%) efficiently improves the oxidation resistance of Ti₃SiC₂/SiC composites.According to XRD and SEM-EDS results, the oxidized layers of the Ti₃SiC₂/SiC composites are composed of an outer layer of TiO₂(rutile) and SiO₂(amorphous), and a transition layer of mixture of TiO₂ and SiO₂ With the increasing of SiC contents, SiC was oxidized to amorphous SiO₂ especially with the 7mol contents of SiC. At high temperatures (1400℃), the formation of amorphous SiO₂ can influence the growth morphology of TiO₂ layer. The continuous and dense TiO₂ films are formed, which can efficiently prevent or slow the diffusion of oxygen and hinder the diffusion process, and results in good oxidation resistance.