Evaluation of corrosion and tarnish on titanium alloy by electrochemical quartz crystal analyzer

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Although well known for their superior corrosion resistance, titanium and titanium alloys are not strongly resistant to discoloration caused by peroxide and fluoride. This study investigates the tarnish and dissolution of several titanium alloys caused by peroxide or fluoride containing solutions. We found following conclusions. The reactions on titanium in a solution containing fluoride and albumin are demonstrated based on crystal phase, surface composition, released titanium concentration, and pH. The formation of an adsorbed albumin films on the passive film of specimen not only protected the specimen from attack by the fluoride but also suppressed release of titanium. The corrosion resistance of PGA and S12 decreased in iodine, and that of TI decreased in fluoride. Chromium content in Ti-Cr alloys increases the ratio of chromium oxide in surface oxide films. We suggest that oxide films which have rich chromium oxide content have greater corrosion resistance to fluoride. Alloying up to 3.5 mass % Cu to Ti-6Al-4V did not change the corrosion behavior. Specimens with ground or sandblasted surfaces were superior to specimens with as-cast surfaces. The color difference and dissolution rates were different with the two solutions. In the hydrogen peroxide containing solution, the color difference was higher for the Ti-55Ni and the Ti-6Al-4V alloys than any other alloys. Ti,Ti-0.15Pd,Ti-7Nb-6Al,Ti-6Al-4V and Ti-10Cu alloys showed remarkable color differences and dissolution in the fluoride containing solution. Ti-20Cr alloy showed the least color difference and dissolution in both solutions. We could not find significant correlation between color difference and dissolution by electrochemical quartz crystal analyzer.