Surface Strain Measurement of Thermally Sprayed Ceramics Coatings under Static and Cyclic Loadings and Its Application to Detection of Delamination

Thermally sprayed ceramic coatings are commonly used as thermal barriers at high temperature. However, delamination of the coating from substrate (base metal) under various operation conditions, including high temperature and mechanical loads, always leads to serious degradation of the heat shielding effect. It is important to detect the delamination in situ and nondestructively for the maintenance and management of mechanical structures. However, until now, neither a clear definition of the delamination of the coating from the substrate nor an effective method to detect and evaluate the delamination process has been proposed. In this work, the surface strains of a substrate and a thermally sprayed coating were measured using an electronic speckle interferometry (ESPI) method. As a result, generation of delamination of the coating corresponded well to the critical strain e c on the e-σ s curve under a static load, where a large drop in the strain occurred for the coated specimen compared to the substrate only specimen. Furthermore, generation of the delamination under a cyclic load also corresponded well to a large drop in strain for the coated specimen compared to the substrate only specimen.