Towards An In-Situ Capable Method For Measuring Thermal Barrier Coating Thermal Resistance By Induction Phase Radiometry: Experimental Benchtop Demonstration

Abstract

Abstract This study introduces an in-situ approach to measuring the thermal resistance of thin ceramic coatings deposited on metallic substrates using induction phase radiometry. A one-dimensional analytical heat-transfer model is formulated that relates the phase lag between periodically modulated induction heating (with finite penetration depth) and the coating-surface temperature response as a function of coating thermal resistance. By periodically modulating the induction heating signal, a cyclic internal heat source is sustained within the substrate, and the phase lag between the electrical excitation and the coating-surface radiation flux is measured, enabling non-intrusive in-situ evaluation without emissivity calibration or dedicated laboratory conditions. An experimental setup comprising an induction coil, function generator, pyrometer, and data acquisition system is then designed and applied to an end-of-life gas-turbine blade coated with a thermal barrier coating. Frequency-domain phase shifts measured over low modulation frequencies are fitted in a least-squares sense to the analytical model, and the coating thermal resistance is recovered from the best-fit parameters in an overdetermined system. The experimentally recovered thermal resistance shows low overall residual error of 2% relative to the analytical model and with high repeatability, demonstrating robustness for potential field measurements and for future in-situ, routine TBC health monitoring during gas-turbine operational inspection without requiring engine removal.