Effects of growth stress in finite-deformation thermally grown oxide on failure mechanism of thermal barrier coatings

Thermally grown oxide (TGO), besides bringing extra mismatch between layers in thermal barrier coatings (TBCs), induces volumetric expansion and local large deformation in constrained interface, which results in huge growth stress and then causes the spallation of coatings. Therefore, characterization on the dynamic growth of oxide and stress evolution during oxidation is desirable, but still intractable, especially considering local finite deformation. In the present research, the effects of growth stress evolution in the thermally grown oxide(TGO) on failure mechanism of TBCs are investigated through developing both finite deformation mechanics-oxidation growth model and corresponding finite element method (FEM). Results demonstrate that the TGO growth rate decreases as oxidation time increases and is uneven in different positions, which is consistent with the experimental observations. The maximum tensile stress and compressive stress are situated at the peak and valley regions of bond coating layer, respectively. However, the stress distribution in top coating is opposite to that of bond coating. It implies that the thermal stress in the TGO layer dominates the failure of the TBCs. Compared with small deformation analysis, the maximum stress value in finite deformation description is closer to the experimental result, and it is more suitable to evaluate the growth stress induced by the growth of TGO layer.