INTERFACIAL REACTIONS OF THIN TITANIUM ALUMINIDE FILMS WITH AL2O3 FILMS AND WITH SAPPHIRE

Interfacial reactions between thin (approximately 500 A) titanium alum inide films with 30, 50 and 70 at.% aluminum, and both electron-beam e vaporated Al203 and sapphire, were investigated with transmission elec tron microscopy (TEM) and X-ray photoemission spectroscopy (XPS) at 70 0-900-degrees-C. Single-phase aluminides are formed by reacting thin m ultilayered Ti/Al stacks at temperatures below 700-degrees-C. All thre e aluminides react with alumina at 900-degrees-C after 100 s. The reac tion involves in-diffusion of oxygen into, and out-diffusion of alumin um from the aluminide, resulting in titanium enrichment of the alumini de and the formation of titanium oxides. The reaction is spatially lim ited. The observed reactivity of aluminum-rich aluminides with Al2O3 c ontrasts with all previously reported bulk results, and indicates that on a nanometer scale, titanium aluminides are chemically incompatible with Al2O3.