Simultaneous measurement of TGO thickness and residual stress in thermal barrier coating system via extension of PLPS method

Thermally grown oxide (TGO) is important for the failure of thermal barrier coating system (TBCs). It is significant to nondestructively measure the thickness of TGO and residual stress in TGO. However, it is challenging to simultaneously measure both of them. Here, we extend the photo-luminescence piezo-spectroscopy (PLPS) method to simultaneously measure both the thickness of TGO and the residual stress in TGO. We develop an experimental setup for nondestructive detection of Cr³⁺ luminescence spectrum within TGO in air-plasma-sprayed (APS) TBCs. By extracting the intensity of the R2 peak in Cr³⁺ luminescence spectrum and TGO thickness through SEM observation, we reveal a linear relationship between them. Using the relation, we calculate the TGO thickness of 3600 points with their peak intensities within an experimental zone, and obtained the spatial distribution of TGO thickness. Furthermore, we calculate the residual stress in TGO based on the peak shift data of the Cr³⁺ luminescence spectrum, and obtain the spatial distribution of residual stress in TGO. Subsequently, we obtain the simultaneous variations of residual stress and thickness of TGO. This work enables the simultaneous measurement of the thickness of TGO and residual stress in TGO, providing a potential approach for evaluating failure process of APS-TBCs.