Subsurface oxidation of boron nitride coatings on silicon carbide fibers in SiC/SiC ceramic matrix composites

In a SiC/SiC ceramic matrix composite, oxygen penetrates through unprotected ends of boron nitride coated silicon carbide fibers by ends-on oxidation in ambient air at 1200–1285 °C. For oxidation times and temperatures that cause only a few microns of oxide to form on the matrix, the boron nitride coatings can be oxidized to a depth of several hundred microns. Sub-surface oxide penetration is deeper for thicker coatings.