A nondestructive technique for determining thermal properties of thermal barrier coatings

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.