Microtopographic inspection of laser-glazed thermal barrier coatings

Thermal barrier coatings (TBCs) are extremely useful in gas turbine engines. The quality of these coatings can be improved by subjecting their surface to laser glazing. A reduction in surface roughness, eliminating open porosity on the surface, and the generation of a controlled segmented crack network, can be achieved. TBCs consisting of atmospheric plasma sprayed (APS) ZrO2-8%wtY(2)O(3) are subjected to a CO2 continuous wave laser glazing process to seal their surface porosity, generating an external dense layer. Different amounts of irradiation are applied to the specimens. The microtopograpic inspection of the samples reveal a significant decrease of the surface roughness after laser treatment. However, a network of surface cracks, dependent on the laser scanning speed and track overlapping, are noticed. The cracks have a tendency to be oriented in two perpendicular directions, one in the direction of the laser beam travel direction, the other perpendicular to it. Cracks parallel to the beam scanning direction are found to be at the overlapping zone, in the edge of the subsequent track. (C) 2008 Society of Photo-Optical Instrumentation Engineers.