High-temperature mechanical properties of Si-B-C-N-precursor-derived amorphous ceramics and the applicability of deformation models developed for metallic glasses

The characterization of Si-B-C-N amorphous ceramics using isothermal compression creep testing in the temperature range of 1200 degrees -1500 degreesC is repor ted. The deformation rate contains a stress-dependent component that is proportional to the applied stress, which indicates that this portion of the deformation mechanism is based on viscous flow. An increase in the creep resistance is observed, following either preliminary annealing or hot isostatic pressing, which may be explained by a reduction of free volume in the amorphous material. The application of two deformation models that are used to predict similar deformation behavior in metallic glasses also is discussed. Although both models accurately predict the time dependence of the deformation rate of precursor-derived amorphous ceramics, the free-volume model fits the observed temperature dependence better than the "two-step" rearrangement model.