The stress distribution around holes in thermal barrier coatings

The residual stress distribution in the thermally grown oxide (TGO) around holes in thermal barrier coatings has been measured using luminescence piezospectroscopy. Far removed from the holes the residual stress field in the oxide is equi-biaxial and independent of position but in the vicinity of the holes, the mean stress decreases monotonically towards the edge of the hole. The characteristic distance over which the stresses vary is of the order of the half the hole radius, typically 10–100 times the thickness of the TGO, consistent with a shear-lag model for stress redistribution. The measurements also indicate that the stress distribution in the TGO is unaffected by the presence of an as-deposited thermal barrier coating.