US Patent 7501187 Thermal barrier coating method and article

An outwardly grown diffusion aluminide bondcoat is formed on a superalloy substrate and has higher concentrations of Al and Pt and lower concentrations of harmful impurities (e.g. Mo, W, Cr, Ta, S, etc.) at an outermost region of the bondcoat than at an innermost region thereof adjacent the substrate. The bondcoat is pretreated prior to deposition of a ceramic thermal insulative layer in a manner that reduces grain boundary ridges on the outermost bondcoat surface without adversely affecting the outermost region thereof, and then is heat treated to thermally grow a stable alpha alumina layer on the bondcoat prior to deposition of a ceramic layer.