Interface failure and stress evolution of thermal barrier coatings under double-layer oxide growth

Abstract

In the high temperature service environment for a long time, thermal barrier coatings (TBCs) generate a double layer of thermally grown oxide (TGO) consisting of an Al2O3 layer and a mixed oxide layer (MO) between the internal top coat layer (TC) and the bond coat layer (BC). Among them, the late generated MO is highly susceptible to the formation and expansion of microcracks within the coating due to its looseness and porosity and brittleness, which leads to premature spalling of the coating. Therefore, in this paper, based on the diffusion-oxidation model of double-layer TGO growth, the failure and stress evolution process of the coating interface under the anisotropic growth of double-layer TGO within TBCs is investigated by using the birth-death element method, considering the nonlinear deformation behavior of the material. The results show that the growth of MO will significantly increase the level of tensile stress at the coating interface, which will easily lead to damage and failure of the MO/TC interface in the peak area at the high temperature stage and in the center of the slope at the cooling stage, failure of the MO/TC interface causes higher tensile stresses at the peak of the BC layer and promotes the destruction of the Al2O3/BC interface from the peak to the valley during the cooling stage; after the failure of the MO/TC interface, the increase of hAl2O3/hMO accelerates the damage of the Al2O3/BC interface.

Keywords

• thermal barrier coatings
• double-layer thermally grown oxide
• interface failure
• anisotropic growth