Corrosion of Titanium and Titanium Alloys

Titanium is extremely unstable in air or water, yet Ti and its alloys are highly corrosion resistant in a wide range of environments, due to the exceptional protection afforded by the ubiquitous oxide film that is formed spontaneously on the material or grown by anodization. Under low pH conditions, including the crevice interior in cases of crevice corrosion, where the oxide dissolves and unalloyed Ti is susceptible to corrosion attack, minor alloying additions (< 0.1 wt%) of noble elements enhance the corrosion resistance, restoring passivity via the cathodic modification mechanism. The most dangerous corrosion processes for the longevity of Ti and Ti alloy structures tend to be crevice corrosion and embrittlement effects associated with hydrogen absorption into the bulk metal. This article very briefly describes: the relatively short history of metallic Ti; the main features of its electrochemical behavior; the influence of alloying on the corrosion performance, including cathodic modification; and the process of crevice corrosion as it applies to Ti and Ti alloys.