Bondcoat surface modification to improve thermal barrier coating lifetime

MCrAlY bondcoats produced by atmospheric plasma spray are inherently rough. Ceramic YSZ topcoat adhesion is a direct function of bondcoat roughness however the rough surface can be detrimental to topcoat adhesion under high temperature cycling. Growth kinetics and chemical composition of the TGO layer differs between convex/concave regions of the bondcoat. De-lamination occurs primarily at the convex regions and leads to crack propagation. In this study, we report the removal of convex regions to improve YSZ topcoat lifetime by suppression of crack formation. Convex asperities of the CoNiCrAlY bondcoat were removed prior to APS YSZ topcoat deposition. Removal resulted in a morphology consisting of concavities and polished flats. TGO growth and composition were measured after 1100 °C isothermal exposure over 100 hours and compared to the unmodified bondcoat morphology. Modification was found to decrease the growth of spinel type oxides on the topcoat/TGO interface compared to unmodified bondcoats. Variation in TGO growth rates between concave and polished regions in the modified bondcoats was determined to be smaller than the variation in growth rates between concave and convex regions in the unmodified bondcoats. YSZ adhesion did not differ significantly between modified/unmodified systems, prior to and after isothermal exposure.