Surface reactivity of titanium–aluminum alloys: Ti₃Al, TiAl, and TiAl₃

Titanium‐based alloys, and Ti–Al alloys in particular, are of special interest due to the technological importance of these materials as structural materials in aggressive environments. The surface chemistry of 1000‐Å films of Ti₃Al, TiAl, and TiAl₃, prepared by codeposition in an ultrahigh vacuum system, has been examined by x‐ray photoelectron spectroscopy (XPS). The alloys are examined as deposited and after treatments from room temperature to 600 °C in either vacuum of 5×10⁻⁷ Torr or 5×10⁻³ Torr O₂. The alloys are compared with one another with regard to their surface segregation and oxide overlayer formation. Particular attention is given to the nature of the surface oxide that develops under the various conditions, and low take‐off angle XPS is used to determine the depth distribution of the various oxides present. The oxidation process is controlled by temperature, oxygen pressure, the bulk alloy composition and the free energies of formation for the various oxides found in the overlayers.