Phase of thermal emission spectroscopy for properties measurements of delaminating thermal barrier coatings

Abstract

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.

IFFT-Based Microwave Non-Destructive Testing for Delamination Detection and Thickness Estimation

“…Here, the thickness of the delamination region between the dielectric and the back metal (d 2 ) is increased from 0 mm to 2.6 mm, with a 0.1 mm step. Applying the proposed technique to the simulated frequency domain reflection coefficients for each step resulted in the delamination estimation shown in Figure (9). The estimated delamination thickness for this arrangement has a margin of error of about 0.1 mm due to the assumptions applied in the estimation technique.…”

Differential phase of photothermal emission analysis for thermal property measurement of thermal barrier coatings

“…Despite its vital nature, in practice the desired level of thermal characterization in TBC production and service is currently unattained because of the inability of conventional techniques to measure coating thermal properties on engine hardware. Thermal imaging has been employed to detect delamination of coating materials [9]. However, mechanical failure of the coating is only one aspect of a TBC's "health" that indicates approach to end of life.…”

Non-destructive measurement of top coat thickness in TBC systems by 3D optical topometry

“…Traditionally, the widely applied methods of evaluating the degree of the TBC layers' wear are: 'dry' impedance spectroscopy, [6,8,9] room temperature electrochemical impedance spectroscopy, [10,11] photo stimulated luminescence spectroscopy [12 -15] and phase of thermal emission spectroscopy. [16] For the evaluation of the delamination degree, some studies [17,18] proposed the method of infrared thermography, another study [19] applied acoustic emission and some [20,21] used the optical methods of piezospectroscopy and elastic scattering. The last two were successfully applied for the evaluation of the thickness of the TBC layers obtained by the Electron Beam Physical Vapor Deposition (EB-PVD) method, as opposed to the plasma sprayed layers, [22] which involve a wider application of the mid-infrared reflectance method.…”