Residual stress and damage effect on integrity of ground silicon nitride

Ceramic workpiece integrity and residual surface stresses generated by single pass diamond grinding were evaluated for three flaring cup wheels and four machine-loop stiffnesses. Stresses in silicon nitride bars ground on one face were characterized by X-ray diffraction, strength by four-point bending, and grinding damage depth by scanning electron microscopy. A custom-built workpiece holder was used to tune the grinding machine-loop stiffness. Electrolytic in-process dressing was applied to one of the wheels to provide stable cutting conditions. The experimental results indicate machine stiffness does not have significant influence on flexural strength, but rather affects the depth of cut. All ground surfaces have some degree of damage and residual stress, and differences are revealed between wheel bonds and grit sizes. The competing phenomena of strength enhancement due to residual stress and strength degradation due to damage are discussed.