Piezospectroscopic Determination of Residual Stresses in Polycrystalline Alumina

The residual stresses created in polycrystalline aluminum oxide as a result of its constrained anisotropic thermal contraction are measured with the technique of piezospectroscopy using the fluorescence from trace Cr 3+ impurities. The average residual stresses in the crystallographic a and c directions are determined as a function of grain size for a high‐purity alumina, as is the width of the stress distribution (assuming it to be Gaussian). Over the range of grain sizes investigated, from 2 to 16 μm, the residual stresses exhibit a dependence on grain size consistent with the prediction of the Evans‐Clarke model of thermal stress relaxation by grain boundary diffusion.