Effects of the amorphous oxide intergranular layer structure and bonding on the fracture toughness of a high purity silicon nitride

The microstructural evolution and structural characteristics and transitions in the thin grain-boundary oxide films in a silicon nitride ceramic, specifically between two adjacent grains and not the triple junctions, are investigated to find their effect on the macroscopic fracture properties. It is found that by heat treating a model Si3N4-2wt percent Y2O3 ceramic for ~;200 hr at 1400 degrees C in air, the fracture toughness can be increased by ~;100 percent, coincident with a change in fracture mechanism from transgranular to intergranular