The Imaging Of Thermal Barrier Coating Based On Microwave Reflection Theory

Thermal Barrier Coating (TBCs) has been widely used in hot components such asengine vanes, for its advantages of heat insulation and high corrosion resistance.However, the thickness of TBCs may be not constant because of complicated process,and the heat insulation property will be affected. After working under hightemperatures for a long time, cracked defects under TC layer will appear. Thesedefects will extend until interfacial debonding, and finally TBCs invalidate. Therefore,it is necessary to detect TBCs with nondestructive test technical, such as the thicknessof TC or initial defects under TC, so that accidents can be prevented.In this paper, the relationship between reflection coefficient and thickness,defects of TBCs were studied, based on the propagation feature of microwave spreadthrough multi layer. Main works are as follow:(1) Set up microwave scan imaging system, this system contains mechanicalscanning mechanism, PXI control system, network analyzer and probe fixture. Thendevelop control and specialty imaging software by using LabVIEW to realizeautomatic scanning detection, data process and imaging.(2) Determine values of standoff distance through simulation study; thenexperimental study has been made between TBCs with different thickness, therelationships between thickness of TBCs and phase difference were established,finally TBCs with different thickness were scanned and imaged.(3) Detection of defects in TBCs was studied by simulation and experimental.Change rules of the optimum detection frequency vs. different thickness weredetermined when standoff distance kept unchanged. Images were obtained by usingphase difference and amplitude at the optimum detection frequency. The resultsshowed, after the approximation reconstruction of wavelet, images could not onlyrepresent the location of defects, but also the size of defects to a certain degree.