In-Situ Stress Measurement of Bond Coatings at High Temperature by High-Energy Synchrotron X-Rays
Kenji SUZUKI, KeisukeTANAKA, Yoshiaki AKINIWA, Masashi KAWAMURA, Kozi NISHIO and Hideki OKADO
Abstract:High-energy X-rays from a synchrotron radiation source, Spring-8, are available to obtain the microstructural information at deep positions inside the materials, because of its large penetration depth. Using the high-energy X-rays with an energy level of about 73 keV, the internal stress in the bond coating was measured through the top coating in the thermal barrier coatings (TBCs) which consisted of a zirconia top coat with thickness of 0.24 mm and a NiCoCrAlY bond coat with thickness of 0.2 mm. A furnace, which could heat up the specimen up to 1473 K was developed for the purpose of the in-situ stress measurement of the TBC in the goniometer at Beam Line BL02B1 of Spring-8. The diffraction of Ni_3Al-311 from the bond coat obtained through the top coat with about 0.24 mm thickness was strong enough for stress determination. The internal stress in the bond coating was measured at the room temperature, 773 K, 1073 K and 1373 K. The internal stress in the bond coat at a room temperature was tensile, and it was decreased with increase in temperature. At 1073 K or higher, the internal stress in the bond coat was released due to softening of the bond coat. The change of internal stresses in the bond coat with temperatures was explained by thermal mismatch of expansion between top and bond coats. Key Words:Thermal barrier coating, Residual stress, Synchrotron radiations, In-situ stress measurement