Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

NDE technique for k/microstructure probe

A new measurement technique, Phase of Thermal Emission Spectroscopy, has been developed to determine the thermal properties of thermal barrier coatings. The measurement is a non-destructive infrared thermography technique in which harmonic heating is induced in the coating by laser excitation and the resulting temperature field is interrogated through its thermal emission. An original analysis of the emission signal has been developed, such that several coating quantities can be determined from the measurements. Two dimensionless thermal parameters of the film can be measured: the thermal diffusivity and the effusively contrast between the film and substrate. From these, the thermal conductivity and the volumetric heat capacity of the film can be calculated. A set of measurements is performed by recording the phase of the thermal emission as a function of laser frequency. The model is used to compare measured phase-shifts with calculated values based on a candidate set of unknown film properties. The film properties are determined by minimizing the sum of the squared errors between measured and calculated phases.

The Phase of Thermal Emission Spectroscopy can be used to map characteristics of the coating, and is sensitive to interface thermal contact, structural aging, structure defects and coating thinning. This provides a means of detecting defects in a non-destructive way, and in particular decohesions near the interface, which can result in spallation. The variable thermal penetration depth of the measurement can be exploited. When contrasting maps at high and low frequencies, delaminations are seen in the low frequency map, but are absent in the high frequency map. In contrast, near surface defects are seen in both frequency maps. In this manner, the relative depth of a defect in the coating can be established.

Informations connexes

Reported by

Univeristy of California, Santa Barbara
Engineering II, Room 2321
CA 93106-5 Santa Barbara
United States