High temperature, oxidation-resistant abradable coatings containing microballoons and method for applying same

An abradable coating composition for use on shrouds in gas turbine engines or other hot gas path metal components exposed to high temperatures containing an initial porous coating phase created by adding an amount of inorganic microspheres, preferably alumina-ceramic microballoons, to a base metal alloy containing high Al, Cr or Ti such as β-NiAl or, alternatively, MCrAlY that serves to increase the brittle nature of the metal matrix, thereby increasing the abradability and oxidation resistance of the coating at elevated temperatures. Coatings having a total open and closed porosity of between 20% and 55% by volume due to the presence of ceramic microballoons ranging in size from about 10 microns to about 200 microns have been found to exhibit excellent abradability for applications involving turbine shroud coatings. An abradable coating thickness in the range of between 40 and 60 ml provides improved performance for turbine shrouds exposed to gas temperatures between 1380° F. and 1800° F. Abradable coatings in accordance with the invention can be used for new metal components or to repair existing equipment. The coatings can be applied to the metal shroud using thermal spray, processes that integrate sintering and brazing, or direct write techniques.