GRAIN-BOUNDARY FRACTURE-RESISTANCE OF SILICON-NITRIDE

The grain boundary fracture resistance in a hot-pressed silicon nitride ceramic (NC132) has been measured directly. The fracture energy relative to that of the bulk material, G(I)/G(M), is found to be similar to 0.3 which is higher than that considered favorable for interfacial fracture and fiber debonding in composites. This is consistent with observations of crack trajectories in the material, which indicate little crack deflection at the fibrous beta-Si3N4, and indentation measurements, which indicate almost no R-curve behavior. The fracture measurements were made on flat, synthetic grain boundaries fabricated by hot isostatic pressing, so that microstructural contributions to the fracture resistance could be avoided.