The adherence of plasma-sprayed thermal barrier coatings (TBCs) is dependent on mechanical interlocking at the interface between the ceramic top coat and the underlying metallic bond coat. A rough bond coat surface is required in order to establish adequate mechanical bonding. However, the resultant interface asperities modify residual stresses that develop in the coating system due to thermal expansion mismatches. These residual stresses induce progressive fracture and eventual spallation of the ceramic top coat. In the case of a flat interface, the residual stress parallel to the interface is of primary concern since the stress normal to the interface is zero. The stress normal to the interface becomes non-zero when the interface has the required interlocking morphology. In the present study, the actual microstructure of a plasma-sprayed TBC system was numerically simulated to analyze the localized residual stress of coating system. Additionally, model microstructures were examined in order to evaluate the manner in which the geometry of interface asperities influences residual stresses.
Citation: Journal of the American Ceramic Society
Pub Type: Journals
finite element analysis, fracture, microstructure, spallation, thermal barrier coatings