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Mechanisms for Interfacial Toughness Loss in Thermal Barrier Coating Systems


 A major concern with thermal barrier coatings (TBCs) is their loss of adhesion during service, leading to spallation. In this research, an indentation test is used to quantify decreases in interfacial toughness of TBC systems as a function of the duration of isothermal or cyclic high-temperature exposures. A detailed description is given of the indentation test, which involves penetration of the TBC and the oxide layer below it, inducing plastic deformation in the underlying metal bond coat and superalloy substrate. This plastic deformation induces a compressive radial stress away from the indent, which drives an axisymmetric delamination of the TBC and oxide layers. Detailed elastic-plastic model results are presented which allow determination of the toughness of the oxide/bond coat interface from a measured radius of delamination.