Characterisation of phase relations and properties in air-oxidised Ti3SiC2

The oxidation of Ti3SiC2 in air from 25 to 1450 °C is characterised by differential thermal and gravimetric analysis (DTA/TGA), X-ray diffraction (XRD), grazing-incidence synchrotron radiation diffraction (GISRD), neutron diffraction (ND), transmission electron microscopy (TEM), secondary ions mass spectroscopy (SIMS) and Vickers indentation. The diffraction results show that rutile formed at a temperature of ~750 °C. A glassy phase - formed at >1000 °C - devitrified upon cooling to room temperature to form tridymite but crystallised to cristobalite at temperatures >= 1300 °C. Composition depth-profiling of the surface layer oxides by XRD, GISRD and SIMS revealed a graded distribution of phases (TiO2, SiO2 and Ti3SiC2) both at the nanoscale (=<1100 °C) and microscale level (>=1200 °C), which is particularly distinct at the interfaces. The oxide layers also exhibit a graded variation in microhardness.