Analysis on Residual Stress Distribution in Oxidized Thermal Barrier Coatings
Kenji SUZUKI, Takahiro KUBO, Keisuke TANAKA and Yoshiaki AKINIWA
Abstract:The distribution of an out-of-plane stress, sigma_3, in a thermal barrier coating (TBC) can be obtained from the combination of the data measured with laboratory X-rays and high-energy synchrotron X-rays. This method is called the hybrid method. To improve the hybrid method, the penetration depth is taken into account in the relation between a diffraction angle, 2theta, and sin2psi. The distribution of the in-plane stress, sigma_1, was obtained by the stress measurement with laboratory X-rays after successive removal of the surface layer. Assuming the distribution of sigma_3 as a cubic function, the parameters of the function were optimized by minimizing the error between the measured and calculated 2theta-sin^2psi relations. In the top coating oxidized for 500h at 1373K, the out-of-plane stress became large tension near the interface between the top and the bond coating due to the interface roughness and the thermally grown oxide (TGO). For the top coating oxidized for 1 000h, the TGO more grew and the out-of-plane stress near the interface was released due to the initiation of spalling cracks. However, the in-plane stress was maintained and the compressive stress region was extended. As a result, the behavior of the degradation of the oxidized TBCs corresponded to the change in the distributions of the residual stress. Key Words:Thermal barrier coating, Spalling stress, Synchrotron radiation, Thermally grown oxide, Residual stress, Hybrid method, X-ray penetration depth