The Structure of Slow Crack Interfaces in Silicon Nitride.

摘要

Cracks in hot-pressed silicon nitride (HPSN) and in reaction bonded silicon nitride were studied by light and electron microscopy. Slow crack growth,resulting from plastic deformation,occurred in HPSN at 1400C. However,the RBSN exhibited brittle fracture at this temperature. This difference in behavior can be explained by the effects of compositional and microstructural differences between the two materials. The MgO additions to HPSN promoted sintering but its presence contributed to plastic deformation. The RBSN was made without added phases. It does not sinter as completely as the HPSN and the grain size is an order of magnitude smaller. The small grained regions offered no resistance to fracture.