Influence of fiber-matrix bond strength on the performance of Nicalon/CAS-II composite

The influence of the fiber-matrix interphase on the tensile behavior of unidirectional Nicalon fiber-reinforced CAS-II glass-ceramic matrix composite has been investigated. The failure strain decreases at high temperatures (1000°C) to a value comparable to the matrix cracking strain. The embrittlement process appears to be the result of oxidation of the carbon interphase as the matrix crack encounters fibers (given sufficient strain and/or time), the interphase subsequently fuses with a high bond strength and the crack grows through the fibers. In the absence of matrix cracking (at high temperatures) the oxidation process does not penetrate more than a few fiber diameters in from exposed surfaces transverse to the fiber direction. The contribution of the degradation of the fibers to the embrittlement appears to be less important.