Abstract
The use of thermal barrier coatings (TBC) for turbine blades in gas turbine engines has allowed higher engine operating temperatures exceeding 1200℃ at the surface of the TBC top coat. More recently, it has been recognized that at these high temperatures the TBCs can be damaged by calcium-magnesium-alumino-silicates (CMAS) resulting from siliceous minerals (dust, sand, ash) containing the intake air and from unclean fuels such as a syngas and biomass gas. In the present study, the CMAS damage was simulated in laboratory employing a synthetic CMAS product on Air Plasma splayed (APS) and Electron Beam Physical Vapor Deposition (EB-PVD) thermal barrier coatings. The changes in microstructure and mechanical characteristics were characterized after isothermal exposure at 1200-1250℃ for various times. Microstructural observation showed the ingression of the CMAS into the TBC top coat, the dissolution of the TBC top coat into the CMAS and the phase transformation of the TBC top coat. It was found from micro-indentation testing of the TBC top coat that shorter exposure time increased the hardness, but longer exposure time decreased the toughness. Based on these results, the effect of the CMAS product on the delamination behavior of the TBC top coat was assessed.
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