CRACK-PROPAGATION BEHAVIOR OF CVD SI3N4-TIN COMPOSITE EXAMINED BY HIGH-RESOLUTION ELECTRON-MICROSCOPY

Crack propagation behavior of a chemical vapor deposited (CVD) Si3N4-T iN composite was investigated by microindentation fracture (MIF) and h igh-resolution electron microscopy (HREM) techniques. TiN fibers are h omogeneously dispersed in large Si3N4 grains (about 8 mum in diameter) , leading to an intragranular nano-composite structure, and their inte rfaces were directly bonded without any other phases. The main fractur e mode is a mixed type of intergranular and transgranular fracture. Na nometer-sized TiN dispersed in the matrix grains interacts with cracks , generating crack bridging and microcracking which toughens the compo site.