Abstract: The objective of this study is to investigate feasibility of millimeter wave nondestructive testing to detect the defects of TBCs and to determine sensitivity of detection when frequency changed. The simulation to monitor the delamination of TBCs and TGO are carried out using computer simulation technology-microwave studio. WR18 rectangular waveguide (40-50 GHz) and WR14 rectangular waveguide (50-60 GHz) are used to detect the delamination of TBCs. The depth of cracks (parallel to the interface of TC and BC), the size of the shape of delimation, the thickness of delimation are studied. Four rectangular waveguides, including WR42 (18-26.5 GHz), WR28 (26.5-40 GHz), WR18 (40-50 GHz) and WR14 (50-60 GHz), are used to detect TGO. The changes in the phase of reflection coefficient are primarily studied. The results show that the phase difference of reflection coefficients can represent not only the existence of the defect, but also the depth of the defect. When the delamination surface is less than the aperture of the waveguide probe, the phase of reflection coefficient can represent the size of delamination. When the delamination surface is more than the aperture of the waveguide probe, the phase of reflection coefficient can represent the thickness of delamination. The phase difference of reflection coefficient can represent the TGO thickness. Besides, the sensitivity is greater in high frequency than low frequency.

Key words: Delamination, Millimeter wave, Nondestructive testing, Thermal barrier coatings, Thermal growth oxide