Effect of Heat Treatment on Young’s Modulus and Poisson’s Ratio of Thermal Barrier Coating Studied by Bending of Three-Layered Specimen

Abstract

Thermal barrier coating (TBC) is a key technology for prolonging the life of the hot sections of gas turbine and airplane engines. A TBC system has a three-layered structure comprising a substrate, bond coat (BC), and TBC topcoat (TC). Young’s moduli and Poisson’s ratios of the coatings are important for calculating the parameters of material mechanics in the TBC system. However, research on Poisson’s ratio is scarce owing to the difficulty of its evaluation. The objective of this paper is to investigate the effect of high temperature exposure on Poisson’s ratios of yttria-stabilized zirconia TC and CoNiCrAlY BC. For this purpose, we evaluated the time-dependent Young’s moduli and Poisson’s ratios of coatings thermally treated at 600 °C to 1000 °C using the bending method. Our measurement revealed that an increase in Poisson’s ratios of the TC and BC as well as Young’s moduli depended on the temperature and length of exposure. The increasing rate in Poisson’s ratios was lower than that of Young’s moduli for both the TC and BC. These phenomena were explained by focusing on the microcracks and pores of the coatings.