STRENGTHENING AND TOUGHENING OF SILICON-NITRIDE BY SUPERPLASTIC DEFORMATION

Mechanical properties of silicon nitride which was superplastically de formed in plane-strain compression were investigated. Superplastically deformed silicon nitride exhibited a highly anisotropic microstructur e, where rod-shaped grains tended to be aligned along the extruding di rection. The bending strength and fracture toughness were increased su bstantially by the deformation process when a stress was applied in th e extruding direction. It appears that these improvements were mainly due to effective operation of grain bridging and pull-out by the grain alignment.