Coherent gradient sensing method for measuring thermal stress field of thermal barrier coating structures

- Coherent gradient sensing method is applied to measure the thermal deformations of thermal barrier coatings at high temperature.
- The thermal stress field through the entire thermal barrier coatings system is obtained by experiment and finite element method (FEM) analysis.
- The residual stress due to the spraying procedure is proved to have little effect on the substrate deformation.

Coherent gradient sensing (CGS) method can be used to measure the slope of a reflective surface, and has the merits of full-field, non-contact, and real-time measurement. In this study, the thermal stress field of thermal barrier coating (TBC) structures is measured by CGS method. Two kinds of powders were sprayed onto Ni-based alloy using a plasma spraying method to obtain two groups of film-substrate specimens. The specimens were then heated with an oxy-acetylene flame. The resulting thermal mismatch between the film and substrate led to out-of-plane deformation of the specimen. The deformation was measured by the reflective CGS method and the thermal stress field of the structure was obtained through calibration with the help of finite element analysis. Both the experiment and numerical results showed that the thermal stress field of TBC structures can be successfully measured by CGS method.