Microwave Inspection of Thermal Barrier Coating (TBC) Systems

Abstract

Nondestructive testing (NDT) of thermal barrier coating (TBC) systems is a critical issue in their manufacturing environments. In particular, inspection techniques by which thickness of TBC topcoat can be accurately determined are currently being sought. This work investigates the use of open-ended rectangular waveguide probes at frequencies in the range of 26.5-70 GHz for evaluation of TBC topcoat thickness. In addition, the influence of volumetric porosity level on thickness measurement accuracy is considered. This investigation encompasses electromagnetic modeling and experimental efforts that are shown to result in the ability to estimate topcoat TBC thickness to within ±1 mil.