The present invention generally relates to protective coating systems suitable for components exposed to high temperatures, such as the hostile thermal environment of a gas turbine engine. More particularly, this invention relates to slurry coating compositions and processes for selectively enriching surface regions of a component, for example, the under-platform regions on a turbine blade, with corrosion-resistant metals such as chromium.
Components of turbine engines, such as the blades and vanes (nozzles) within the turbine section of a gas turbine engine, are often formed of an iron, nickel, or cobalt-base superalloy. A turbine blade has an airfoil against which hot combustion gases are directed during operation of the gas turbine engine, and whose surface is therefore subjected to severe attack by oxidation, corrosion and erosion. The blade further includes a platform and an under-platform or root section separated from the airfoil by the platform that, while not directly exposed to hot gas path, are still exposed to high temperatures and are susceptible to oxidation and corrosion. Turbine blades are typically anchored to the perimeter of a rotor or wheel by forming the rotor to have slots with dovetail cross-sections that interlock with a complementary dovetail profile on the root section of each blade.