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

Interfacial reactions between thin (approximately 500 A) titanium aluminide films with 30, 50 and 70 at.% aluminum, and both electron-beam evaporated Al203 and sapphire, were investigated with transmission electron microscopy (TEM) and X-ray photoemission spectroscopy (XPS) at 700-900-degrees-C. Single-phase aluminides are formed by reacting thin multilayered Ti/Al stacks at temperatures below 700-degrees-C. All three aluminides react with alumina at 900-degrees-C after 100 s. The reaction involves in-diffusion of oxygen into, and out-diffusion of aluminum from the aluminide, resulting in titanium enrichment of the aluminide and the formation of titanium oxides. The reaction is spatially limited. The observed reactivity of aluminum-rich aluminides with Al2O3 contrasts with all previously reported bulk results, and indicates that on a nanometer scale, titanium aluminides are chemically incompatible with Al2O3.