Focus effect of photoluminescence piezospectroscopy and its influence on the stress measurement of thermally grown oxide in thermal barrier coatings

The residual stresses in thermally grown oxide (TGO) on a Fecralloy substrate were measured by photoluminescence piezospectroscopy (PLPS). It was found that the distance between the laser focus and the TGO surface has a remarkable effect on the peak shifts measured by PLPS. Further examinations on the TGO in thermal barrier coatings (TBCs) confirmed this effect, indicating that the presence of a TBC will affect the stress measurement in the TGO.