Temperature Estimation and Aluminum-Content Prediction Focusing on Microstructural Change of Bond Coat in Thermal Barrier Coating

Abstract

In order to develop an estimation method of local temperature in thermal barrier coating (TBC), we observe the change in the microstructure of a CoNiCrAlY bond coat (BC) tested under oxidation in air at high temperatures. An oxide layer grows at the boundary between the BC and top coat (TC) while an Al-decreased layer appears underneath it. The thickness of the Al-decreased layer increases in proportion to the square root of the test time, and the growth rate can be described by the Arrhenius equation. The relationship among the layer thickness, time and temperature is formulated by the experimental results. Then, the temperature at the BC in a gas turbine component can be estimated by measuring the layer thickness on the basis of the relation. As the thickness of Al-decreased layer cannot exceed the BC thickness, there is the application limit. Moreover, the TC/BC boundary possesses eminent asperity, it brings about the error in the temperature estimation. The application limit and the fluctuation are assessed. The average Al-content in the BC is also measured by mean of an electron probe microanalyzer. The Al-content decreases in proportion to the thickness of Al-decreased layer. A prediction method of the Al-content is proposed on the basis of the relation.