Bending Strength of Wetly and Dryly Ground Y-TZP

Specimens of tetragonal zirconia containing 3mol% Y2O3 were ground wetly and dryly with a grinding wheel of grain size 200/230. The residual stress and the monoclinic content were measured by the X-ray diffraction method. The monoclinic content on the surface ground wetly with enough coolant was raised to about 7 percent. For wet ground Y-TZP, bending stress was applied in directions parallel and perpendicular to the grinding direction. The bending strength in both directions increased because of compressive residual stress. Fracture did not start from grinding cracks. For Y-TZP ground dryly without coolant, the bending stress was applied in the direction pallaled to the grinding direction. Many grinding cracks were introduced on the ground surface and no compressive residual stress was measured. Since the ground surface was heated to a high temperature, the transformation to the monoclinic phase did not occur. The bending strength of dry-ground Y-TZP was reduced remarkably. The breadth of X-ray line broadening measured on the dry-ground furface was larger than that of the wet-ground surface. The depth of the grinding-affected zone was 10μm for the dry-ground surface and 30μm for the wet-ground surface.