Life Prediction of Atmospheric Plasma-Sprayed Thermal Barrier Coatings Using Temperature-Dependent Model Parameters
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Life Prediction of Atmospheric Plasma-Sprayed Thermal Barrier Coatings Using Temperature-Dependent Model Parameters B. Zhang1 • Kuiying Chen2 • N. Baddour1 • P. C. Patnaik3
Submitted: 7 November 2016 / in revised form: 3 April 2017 / Published online: 8 May 2017 ASM International 2017
Abstract The failure analysis and life prediction of atmospheric plasma-sprayed thermal barrier coatings (APS-TBCs) were carried out for a thermal cyclic process. A residual stress model for the top coat of APS-TBC was proposed and then applied to life prediction. This residual stress model shows an inversion characteristic versus thickness of thermally grown oxide. The capability of the life model was demonstrated using temperature-dependent model parameters. Using existing life data, a comparison of fitting approaches of life model parameters was performed. A larger discrepancy was found for the life predicted using linearized fitting parameters versus temperature compared to those using non-linear fitting parameters. A method for integrating the residual stress was proposed by using the critical time of stress inversion. The role of the residual stresses distributed at each individual coating layer was explored and their interplay on the coating’s delamination was analyzed. Keywords APS-TBC critical time for stress inversion CTE mismatch fitting parameter life prediction
& Kuiying Chen [email protected] 1
Department of Mechanical Engineering, The University of Ottawa, Ottawa, Canada
2
Structures, Materials and Manufacturing Laboratory, Aerospace Portfolio, National Research Council Canada, Ottawa, Canada
3
Gas Turbine Laboratory, Aerospace Portfolio, National Research Council Canada, Ottawa, Canada
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Introduction Thermal barrier coatings (TBCs), consisting of a yttria partially stabilized zirconia (YSZ) top coat and a metallic bond coat (BC) deposited onto a superalloy substrate, are favorably used as the protective coatings of hot section components such as combustion chambers, turbine nozzle guide vanes and turbine blades in advanced gas turbine engines. These coatings can withstand high inlet temperatures, thus increasing engine efficiency and improving the life of the components (Ref 1-8). While the YSZ layer has low thermal conductivity and provides thermal insulation to the component, the metallic bond coat enhances the adhesion of the YSZ layer to the substrate and also provides oxidation and corrosion protection to the substrate metal (Ref 9-14). A general understanding about TBCs failure is that biaxial compressive stresses are built up at the interface between the ceramic top coat and the bond coat during cooling from elevated to ambient temperatures because of the thermal expansion mismatch between the two constituents. The biaxial compressive stresses produce a tensile stress normal to the coating plane due to local tortuosity of the interface plane morphology. The tensile stress that acts on pre-existing flaws and defects thus promotes crack nucleation and delamination in th
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