Electron microscopy study on the high-temperature oxidation of Si3N4-TiN ceramics: in situ and ex situ investigations

Oxidation of the composites starts at 650 °C, when TiN surface particles begin to oxidize and form on their exposed surface islands of nanocrystalline TiO2. At around 950 °C, the glass transition temperature of the intergranular glass phase, these nanocrystals start to grow laterally on the surface. At the same time, oxidation progresses into the depth of the material, forming thereby several distinguished oxidation subscales. The intergranular glass plays a crucial role for the oxidation in the temperature range between 950 and 1100 °C. Depending on the glass quantity in presence, different reaction mechanisms dominate; the oxidation kinetics are strongly controlled by the transport within the intergranular glass.