Abstract
The high-temperature oxidation of a silicon nitride-titanium nitride (Si3N4-TiN) composite has been investigated via scanning electron microscopy and energy-dispersive and wavelength-dispersive spectrometry. At 1150degreesC, the oxidation of both the silicon nitride and titanium nitride phases takes place. Several oxidation processes act simultaneously and/or successively. First, the oxidation of the titanium nitride occurs and leads to the formation of a continuous titanium oxide (TiO2) crystal layer at the surface. Next, the TiO2 formation takes place in the sublayer at the same time as the Si3N4 oxidation. The oxidation of this last phase leads to the formation of vitreous silica (SiO2). For long a duration of oxidation (>50 h), a continuous layer of SiO2 is formed under the outer TiO2 scale. Large pores grow in this layer and deform the outer oxide layers, whereas the oxidation occurs in the material. Based on these results and bibliographical data, a phenomenological model is proposed to describe the stages of the high-temperature oxidation of Si3N4-TiN materials.