Residual Stress Change in Thermal Barrier Coating Due to Thermal Exposure Evaluated by Curvature Method

Abstract

Thermal barrier coatings (TBCs) are used to protect the hot sections of gas turbine and jet engines. A TBC system comprises of a substrate, bond coat (BC), and TBC top coat (TC). The residual stress development mechanism by high temperature exposure in TBC is important in designing a high-performance TBC. However, quantitative studies of the stress change and its modeling are few because of its difficulty. The objective of this study is to reveal the changing mechanism of coating stress under high temperature exposure. For this purpose, we applied a three-layered beam model to evaluate the TBC’s residual stress using the curvature change. Time-dependent residual stresses in the TC and BC thermally exposed at 600-1000 °C were evaluated by the curvature method. Subsequently, we investigated the stress-generating mechanism of the coatings by using a finite element analytical (FEA) model that reproduces the measured curvatures. Our experimental result revealed that the residual stress in the BC changed from tensile to compressive by thermal exposure. However, thermal exposure had an insignificant effect on the residual stress in the TC. These changes in coating stress, including temperature and time dependency, were consistently explained by stress relaxation in the BC using the FEA model.