Factors Influencing Residual Surface Stresses due to a Stress‐Induced Phase Bansformation

An X‐ray diffraction technique was used to measure the residual surface stresses on ground surfaces of Al 2 O 3 /ZrO 2 (tetragonal) composites. To accomplish this, it was necessary to use a radiation for which the penetration depth was small (large wavelength), e.g. CrKα radiation. It was found that these materials could have compressive stresses as high as 1 GPa on their surface, which is a result of the molar volume associated with the tetragonal‐to‐monoclinic ZrO 2 phase transformation. This transformation was induced by the grinding stresses and a reasonable correlation between the amount of ZrO 2 transformed and the magnitude of the residual stresses was established. Evidence was found that the transformation depth is controlled by the amount of stabilizing oxide added to the ZrO 2 and by the ZrO 2 grain size. In the materials studied, transformation depths were found to be typically <20 μm.