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 compre ssion creep testing in the temperature range of 1200 degrees -1500 degreesC is repor ted. The deformation rate contains a stress-dependent component t hat is proportional to the applied stress, which indicates that this portio n of the deformation mechanism is based on viscous flow. An increase in the creep resistance is observed, following either preliminary annealing or ho t isostatic pressing, which may be explained by a reduction of free volume in the amorphous material. The application of two deformation models that a re 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-volu me model fits the observed temperature dependence better than the "two-step " rearrangement model.