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.