Models of High‐Temperature, Environmentally Assisted Embrittlement in Ceramic‐Matrix Composites

The intermediate‐temperature oxidation embrittlement, or ‘pest,’ effect found in ceramic‐matrix composites (CMCs) is shown to have features analogous to stress corrosion cracking. The behavior involves crack growth upon oxidation of the fibers or the fiber coatings to form an oxide that weakens the fibers. It has reaction‐ and diffusion‐controlled regimes. The former occurs at low stresses. The latter occurs at higher stresses. It is controlled by oxygen ingress through the matrix cracks. There is also a crack growth threshold. Expressions for the crack velocity above the threshold are derived as well as the stress dependence of the rupture life.