Thermal barrier coating system plays key role in high temperature gas turbine blades. During the manufacture and in-service processes, defects are inevitable due to the inconsistent deformation and fatigue loading. The typical defects, e.g. interfacial debonding and crack in substrate, may significantly degrade the performance, safety and service life of gas turbine. However, it is challenging to non-destructively evaluate the small defects and/or coexistent multi-defects in thermal barrier coating system. Here, we propose a non-destructive method to detect the defects in thermal barrier coating system using the results of both infrared thermography and eddy current testing. Using this method, we detect interfacial debonding as small as 0.7 mm within 0.2 s and identify defect types which are essential for turbine blade fabrication and maintenance. By leveraging multi-physical fields, we achieve effective and quantitative evaluation of coexisting defects in thermal barrier coating system. This method integrates multiple non-destructive evaluation techniques and provides an approach to assess defects in multilayer structures without damaging them.

Raman spectroscopy is an indispensable method for the nondestructive testing of semiconductor materials and their microstructures. This paper presents a study on the angle-resolved intensity of polarized micro-Raman spectroscopy for a 4H silicon carbide (4H-SiC) wafer. A generalized theoretical model of polarized Raman intensity was established by considering the birefringence effect. The distributions of angle-resolved Raman intensities were achieved under normal and oblique backscattering configurations. Experiments were performed on a self-built angle-resolved Raman system, which verified the validity of the proposed model and achieved the identification of crystal orientations of the 4H-SiC sample.