Relationship between X-Ray and Mechanical Elastic Constants of CoNiCrAlY Coating

A thermally sprayed MCrAlY alloy coating in a thermal barrier coating system, called a “bond coat” (BC), is applied to the hot sections of gas turbines and jet engines. Residual stress in the BC is generated during spraying and after thermal exposure. Residual stress in sprayed coatings is an important characteristic that determines the development of high-performance materials and processes. X-ray diffraction is useful for evaluating the residual stress as well as the in situ stress change during thermal exposure. The X-ray elastic constants, which are necessary for evaluating the residual stress using this method, result in an accurate evaluation of the residual stress of a thin coating layer. However, systematic research on the effects of microstructural changes has yet to be conducted. In this study, the influence of high-temperature exposure on the X-ray elastic constants of an atmospheric-plasma-sprayed (APSed) BC was investigated by bending a two-layer specimen. Additionally, a dense high-velocity oxygen fuel (HVOF) BC was evaluated to elucidate the influence of sliding splat particles. Finally, the relationship between the X-rays and mechanical elastic constants of the BC was studied. It was found that the X-ray elastic constants of the as-sprayed APS BC were higher than the mechanical elastic constants due to the sliding deformation between the splat particles. Similarly, the X-ray elastic constants of HVOF BC were higher than the mechanical constants, as same as APS BC. However, the difference between the elastic constants was smaller than that of APS BC. The influence of sliding deformation of both coatings was suppressed by thermal exposure, and the X-ray elastic constants approached the mechanical constants.