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A nondestructive technique for determining thermal properties of thermal barrier coatings is developed. Harmonic heating of the film is established using a laser, while the phase of thermal emission is interrogated from the front surface as a function of laser frequency. The thermal emission phase is related to four film properties: the thru-plane thermal diffusivity, the effusivity contrast between the film and substrate, the optical penetration depth of the laser, and the optical thickness of the film relative to the substrate emissivity at the detector wavelength. From these measurements both the thermal conductivity and volumetric specific heat of the film may be determined. Analysis is illustrated with a set of measurements performed on an electron beam physical vapor deposition coating. Uncertainty associated with fitting multiple film parameters using nonlinear regression is studied.

A linear radiation model is developed that overcomes the analytical complexity in phase of thermal emission spectroscopy. It is shown that the linear radiation model can result in a simple algebraic relation between the phase of thermal emission and four coating properties, enabling these properties to be determined by nonlinear regression analysis of experimental measurements. Suitability of the linear radiation model to various measurement conditions is explored, and the model is applied to the phase of thermal emission measurements performed on a thermal barrier coating.

Phase of thermal emission spectroscopy is developed for determining the thermal properties of thermal barrier coating (TBC) in the presence of thermal contact resistance between the coating and the substrate. In this method, a TBC sample is heated using a periodically modulated laser and the thermal emission from the coating is collected using an infrared detector. The phase difference between the heating signal and the emission signal is measured experimentally. A mathematical model is developed to predict the phase difference between the laser and the measured emission, which considers the coating properties and the thermal contact resistance of the interface. An electron-beam physical vapor deposition thermal barrier coating with local regions delaminated by laser shock is characterized using this technique. The measurements are made on two regions of the coating, one where good thermal contact between the coating and substrate exists and the other where the interface has been damaged by laser shock. The results for the thermal properties and thermal contact resistance of the interface are presented and compared.