Strain-induced stiffness-dependent structural changes and the associated failure mechanism in TBCs

Dynamic structural evolution of thermal barrier coatings (TBCs) during thermal exposure is highly important to account for the failure mechanism of TBCs. In this study, to begin with, the dynamic structural changes were investigated assisted with series of TBCs with different Young's modulus in their top-coat. Results show that the strain-induced structural changes varied from dispersive microscopic inter-tearing to concentrated macroscopic vertical cracks, owing to the gradually stiffening top-coat. Subsequently, the associated failure mechanism of TBCs was revealed based on the stiffness-dependent structural changes. In a gradient thermal cyclic test, gradient stiffening degrees occurred across the top-coat. After certain thermal cycles, some macroscopic vertical cracks were generated in the much stiffer top zone of the top-coat. Consequently, partial delamination occurred when the large vertical cracks are connected with some interfacial cracks. This can be responsible for the failure mechanism of TBCs.