Abstract: A method of non-destructively evaluating a thickness of a coating layer including a coating material on a turbine engine component includes placing first and second probes on an outer surface of the coating layer. The first and second probes are separated by a first distance. The first and second probes are configured to generate an electrical current in the coating layer. The method further includes placing third and fourth probes on the outer surface of the coating layer in a location that is between the first and second probes. The third and fourth probes are separated by a second distance that is less than the first distance. Still further, the method includes generating an electrical current in the coating layer using the first and second probes, measuring the electrical voltage using the third and fourth probes, and calculating the thickness of the coating layer based on the measured electrical voltage.

Abstract: A method of non-destructively evaluating a thickness of a coating layer on a turbine engine component includes directing an acoustic wave into the turbine engine component, the acoustic wave including a frequency and a wavelength, receiving a return time-domain signal reflected from the turbine engine component, and transforming the time-domain signal into a frequency-domain signal. The method further includes subtracting a baseline signal from the frequency-domain signal and determining a local minimum frequency of the baseline-subtracted frequency-domain signal. Still further, the method includes calculating the thickness of the coating layer based on the determined local minimum frequency. Additional evaluation methods including ones based on resistivity, terahertz, and microwave are further disclosed.