Corrosion mechanism of Ti-Cr alloys in solution containing fluoride.

OBJECTIVE The objective of this study was to clarify the influence of chromium content on surface reaction of Ti-Cr alloys in an acidic fluoride-containing saline solution. METHODS Four Ti-Cr alloys containing 5, 10, 15 or 20 mass% chromium were characterized in terms of dissolution of metals in an acidic fluoride-containing saline solution and surface structure by X-ray photoelectron spectroscopy and Auger electron spectroscopy. RESULTS Total amount of metals dissolved from each alloy decreased with increase in chromium content. The surface oxide films of Ti-Cr alloys before and after immersion in an acidic fluoride-containing saline solution consisted of titanic and chromic species, such as oxide, hydroxide, and hydrate. The [Cr]/([Ti]+[Cr]) ratio in the surface oxide film on as-polished Ti-Cr alloys was closely correlated with chromium content. However, the ratio in any alloy approximately doubled after immersion. Although thick oxide films were observed after immersion, all alloys showed a thinner oxide film than commercially pure titanium. SIGNIFICANT In all alloys, concentration of chromic species such as oxide and hydroxide in the surface oxide film was associated with chromium content, and chromic species improved corrosion resistance to fluoride.