The Surface Interaction of Oxygen with a Gamma Tial

Abstract

The composition and bonding of incipient and atmospheric oxides grown on a [gamma]-TiAl (2 at.% Nb) were examined using Auger, x-ray, and low-energy ion scattering spectroscopies. The was determined with secondary-ion mass depth distribution of various components spectroscopy (SIMS). An oxide grown on the material in air at room temperature showed advanced Al and Ti oxide bonding states, which had very different stabilities during heating in vacuum up to 600[degrees]C. The Ti-oxygen bonding state was markedly reduced while the Al oxide was somewhat enhanced during this process. Further controlled studies at 600[degrees]C, involving oxygen adsorption below [approximately]10[sup [minus]6] Torr, showed an initial Al cation surface enrichment until the detectable Al2p peak was 90% oxidized. Further oxygen exposure gradually produced a fully oxidized Ti valence state with a pronounced enrichment of the Ti cation at the vacuum-solid interface. The results are discussed in terms of the kinetic and thermodynamic factors of the rate-limiting steps in the oxidation process.