Residual stress in partially-stabilised-zirconia TBCs: experimental measurement and modelling

The residual stress field in 7wt% yttria partially stabilised zirconia (Y-PSZ) plasma sprayed (300-μm thick) coatings on Al substrates was studied by means of two different techniques: X-ray residual stress analysis (XRSA), and elongation and curvature measurement after substrate removal (CD). Results were considerably improved with respect to conventional XRSA, by using a synchrotron radiation source and specifically designed high resolution optics: an extended beam penetration, achieved by using different wavelengths down to 0.94 Å allowed the determination of the strain field in the outer 50 μm of the ceramic. XRSA (surface) and CD (volume averaged) strain data were analysed by a mechanical model of the coated component capable of integrating the results of both techniques. The procedure, designed to appropriately consider the different nature of the information coming from the two measurement techniques, permitted us to study the residual stress distribution through the entire Y-PSZ coating thickness. In particular, it pointed out the presence of a considerable stress gradient in the surface region of the ceramic.