Evaluation of Residual Stress Distribution in Thermal Barrier Coating System by Extended Thin Layer-Removal Method for Three-Layered Model

Abstract

Thermal barrier coating (TBC) generally consists of top coat (TC), bond coat (BC), and substrate. The TBC system is used for the hot section components of gas turbine engines. It is important to know the accurate residual stress distribution in the TBC system. Thin layer-removal method can evaluate the through-thickness stress distribution based on the strain change of substrate when the coating surface layer is sequentially removed. However, this method has not been applied to a three-layered material. In this study, we proposed an analytical formula for the stress distribution of a three-layered model and a stress correction formula taking into account the stress redistribution of removal layers into the remaining piece. The stress correction formula provides the accurate stress even if the coating is relatively thick compared with the substrate, in which case conventional method is inapplicable. Using the proposed formulae, we experimentally evaluated the through-thickness stress distribution of BC system materials, consisting of substrate and BC (CoNiCrAlY) prepared by atmospheric plasma spraying or high-velocity oxygen fuel spraying. TBC system materials, consisting of substrate, BC, and TC (yttria-stabilized zirconia or alumina) were also evaluated. The obtained stress values and distributions were appropriate to the mechanism of stress evolution (deposition and cooling), indicating that the proposed model is effective for the stress evaluation of three-layered materials.