Aqueous slurry coating system for aluminide coatings

A method for forming a high temperature oxidation resistant protective coating on internal surfaces of a hollow superalloy article which comprises:

• a. providing a slurry consisting of a source of aluminum in particulate form, an inert ceramic particulate, a halide compound activator in particulate form, and an aqueous base dispersant which includes an organic thickening agent and has a viscosity of from about 100 centipoise to 1,000 centipoise;
• b. filling the internal cavity of the article with the slurry;
• c. evaporating the solvent to leave the aluminum source particles, the inert ceramic particles and the halide compound particles in an organic matrix, said matrix resulting from the organic thickening agent;
• and
• d. heating the filled superalloy article to a temperature of between about 1,300.degree. F. and 2,300.degree. F. for a period of between about 1 and about 20 hours in a non-oxidizing atmosphere to decompose the organic matrix, and leave a network of voids, and to permit the halide activator to interact with the aluminum source to generate aluminum compound vapors which coat the internal surfaces and to diffuse into the surface to produce an integral aluminide coating.