Abstract
Platinum Aluminide (PtAl) diffusion coatings play an essential role in the protection of mechanical components exposed to high temperatures, such as gas turbine blades and nozzles. The formation of an adherent oxide scale inhibits substrate oxidation or hot corrosion that would otherwise lead to mechanical degradation and premature failure of parts. Nondestructive evaluation methods of Platinum Aluminide coatings are of significant practical interest in industry to optimize maintenance and repair operations while keeping safety and quality requirements. This article describes the application of a frequency sweeping eddy current technique to measure impedance spectra. Such electrical measurements are then inverted with a classical physics-based model to obtain coating properties (thickness, conductivity) or used to directly estimate useful residual life parameters using data-driven models together with the results of destructive analyses. The article shows the validation of this approach, first on a set of samples artificially aged at different temperature and time exposures up to several years and then the validation on actual parts, that have been removed from service and analyzed in the laboratory. A comparison of the data-driven versus physics model is also presented, showing the pro and cons of each approach.
