A three-dimensional finite element model for the oxide growth mechanism and growth-induced stress within thermal barrier system

Abstract

Thermal barrier coating is subjected to out-of-plane displacements and possible in-plane cracks as thermally grown oxide (TGO) grows at high temperatures. Three different schemes of TGO growth are carried out in a three-dimensional thermal barrier coating model, in order to discuss the growth mechanism of the TGO film and to analyze the growth-induced stress within the top-coat. They are respectively 1) that the TGO film uniformly thickens along the whole thickness; 2) that the TGO film uniformly thickens along the bottom; 3) and that the TGO film linearly thickens at the bottom. The TGO film is found to possess the maximum thickness at the crest and the minimum one at the middle. The difference between the maximum and minimum thicknesses reflects the irregularity of TGO thickness distribution, which causes significant displacement incompatibility within the top-coat. The displacement incompatibility makes the top-coat subjected to out-of-plane compression around the crest and out-of-plane tension around the middle. The TGO growth scheme affects the TGO thickness distribution and the out-of-plane stress within the top-coat. Additionally, the lengthening-to-thickening ratio is employed to study the effect of the lengthening strain rate on the TGO thickness and the top-coat stress. The top-coat stress is very sensitive to the lengthening strain rate, and reducing the lengthening strain rate is helpful in enhancing the lifetime of thermal barrier system.