Effect of interface roughness on internal stress of ceramic thermal barrier coating

Abstract

An investigation was carried out into the effect of the interface roughness between the metallic bond coat and the ceramic topcoat on internal stresses in a thermal sprayed ceramic thermal barrier coating (TBC). To evaluate the effect of the interface roughness on the residual stress in the top coat, the specimens with two kinds of roughness were prepared. The interface roughness oh the bond coat was Ra - 5.8μm for the rough type specimen, and Ra -3.5μm for the smooth type one. The in-plane stresses of the specimens were measured with laboratory X-rays. The in-plane stresses for the both of the rough and smooth specimens were about 60MPa and independent of the roughness of the bond coat. Using high energy X-ray, the stress of the rough specimen was compressive and the stress of smooth specimen was tensile. This tendency is different from the result measured by laboratory X-ray. This difference in the stress value is coursed by the out-of-plane stress. These stresses in the topcoat were estimated by the hybrid method, that is to estimate out-of-plane stress using laboratory X-rays and high-energy synchrotron X-rays. As a result, the larger the roughness of the bond coat became the larger out-of-plane-stress become.