Pest-resistance in SiC/BN/SiC composites

State-of-the-art non-oxide ceramic-matrix composites (consisting of SiC fibers, cvi-BN interphase coating, and mi-SiC matrix) exhibit excellent mechanical properties at room temperature, as well as above ∼1000 °C (where oxidation easily seals flaws with silica); but they are prone to pest degradation at intermediate temperatures in an oxidizing environment, and especially so in the fast, moist flame of a jet engine. Two modes of pest may be distinguished in these composites. The more severe type of pest is promoted by extraneous factors, like a layer of elemental carbon underlying the BN interphase and undermining its intrinsic oxidation resistance. It is shown that, when care is taken to exclude such a carbon layer, SiC/BN/SiC composite can easily survive a 100-h exposure in a burner rig without noticeable loss of strength or strain to fracture.