Surface layer formed by selective oxidation in high-purity copper-titanium binary alloys

X-ray photoelectron spectroscopy (XPS) and secondary mass ion spectrometry (SIMS) have been used for studying surface layers formed by selective oxidation of titanium in high-purity copper-titanium alloys. Sheets of copper-0.5, 1.0, 1.5, 2.0 and 3.4 mass% titanium alloys were annealed at 873 K under a low partial pressure of oxygen. XPS results indicate titanium enrichment on the surface side of a sample to form titanium oxides. With increasing bulk concentration of titanium, the amount of titanium oxides formed on the sample surface increased, while the amount of metallic copper decreased. SIMS depth profiles of these samples showed that titanium oxides are formed in a surface layer less than one micrometer thick, and a titanium-depleted zone is formed beneath the surface layer containing titanium oxides. A concentration profile of titanium formed beneath the titanium-depleted zone was found to be described by outward diffusion of titanium in the matrix, indicating that the oxidation process is mainly controlled by diffusion of titanium in copper.