Characterization of Electron Beam Physical Vapor-Deposited Thermal Barrier Coatings Using Diffuse Optical Reflectance

The use of diffuse optical spectral reflectance as a nondestructive tool to characterize the microstructure of electron beam physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs) has been investigated and the contributions of intercolumnar gaps and intracolumnar pores distinguished. It is shown that the reflectance is controlled by the refractive index mismatch and that the optical scattering coefficient depends on the thickness of the TBC due to the porosity distribution through the thickness of the coating. The sensitivity of the reflectance to the porosity suggests that optical reflectance can be used to characterize the microstructure of EB-PVD TBC for both quality control and nondestructive evaluation purposes.