Residual stress distributions around indentations and scratches in polycrystalline Al2O3 and Al2O3/SiC nanocomposites measured using fluorescence probes

We report a study of the residual stress state around indentations and single point scratches in polycrystalline alumina and alumina/SiC nanocomposites using Cr3+ fluorescence piezospectroscopy. The alumina specimens displayed residual stress levels up to 550 MPa whereas the nanocomposite specimens had maximum stress levels close to 2 GPa. These stress levels are consistent with those obtained using other experimental techniques. The spatial variation of this stress is shown to be consistent with simple elastic/plastic models of indentation. The broadening of the peaks in the fluorescence spectra is used to estimate the density of dislocations in the plastically deformed region below indentations and scratches. Our results indicate a greater depth of deformation around indents and scratches in the nanocomposites when compared with the alumina surfaces. The inferred dislocation densities and the depth of the deformed region beneath the alumina and nanocomposite surfaces are shown to be consistent with those of ground surfaces reported in earlier studies.