The coating life-prediction model, COATLIFE, was previously developed for estimating the lifetimes of first-stage blades and vanes in land-based power-generation gas turbines on the basis of degradation mechanisms observed in laboratory and field data. For first-stage blades with thermal barrier coatings (TBCs), degradation mechanisms treated in COATLIFE include thermo-mechanical fatigue (TMF), Al depletion due to bond coat oxidation, sintering of voids and microcracks in TBC, and curvature effects. Material constants in COATLIFE were evaluated using laboratory data and subsequently utilized with the model to predict the remaining life of first-stage blades in the field. In the present study, the predictive capabilities of COATLIFE were evaluated against field data obtained from first-stage blades with TBC extracted from land-based power generation gas turbines. The ex-service blades were sectioned to characterize the conditions of the TBC and bond coat after various times of service. For coating characterization, the Al content and volume fraction of the β phase in the bond coat, as well as the extent of oxidation and microcracking in the TBCs and along the TBC/bond coat interface at various locations of the blade were determined. These results were compared against model predictions generated by COATLIFE. Good agreement between the field data and model predictions validates the predictive capabilities of COATLIFE for estimating the oxidation lives for first-stage blades with TBCs.

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