Piezospectroscopic characterization of thermal barrier coatings

A technique to measure stress non-destructively with a high spatial resolution using incoherent light scattering and luminescence is presented. The technique employs a Raman microprobe to measure small peak shifts in vibrational and electronic spectra which correlate to applied or residual stresses in the ceramic. The predicted frequency shift for a non-degenerate peak of polycrystalline alumina is estimated from single crystal phonon deformation potentials (PDPs) and secular equations by averaging over all crystal orientations. The predicted shift compares well to the experimentally measured shift. Thermal barrier coatings are analyzed to demonstrate the usefulness of the technique for solving unique mechanics problems in ceramics.