Influence of high-temperature creep stress on growth of thermally grown oxide in thermal barrier coatings

Abstract

Recently, a large local stress has been found, caused by the change of both the diffusion rate of oxygen through an existing oxide and the rate of chemical reaction at the oxide/oxidized material interface. Since high thermal stress occurs in the thermal barrier coating (TBC) system, the volume expansion of the newly grown oxide, and centrifugal force, the growth rate of the thermally grown oxide (TGO) may change depending on the temperature, the exposure time, and the stress. The aim of this study is to make clear the influence of stress on the growth rate of the TGO thickness under static oxidation. The results show that TGO thickening was affected by the increase of not only the exposure temperature but also the applied stress. The tensile stress in a longitudinal direction in a TBC system due to the applied load makes the oxidant transport and oxide flow more easy, i.e., the tensile stress promotes a volume expansion of newly formed oxide. The increase rate of the TGO thickness was approximately 34% when the applied stress increased from 0 to 205 MPa at 900 °C for 325 h, and approximately 25% when the stress increased from 0 to 150 MPa at 950 °C for 125 h.