Will Titanium Metal Become Corrosion?

Will Titanium Metal Become Corrosion?

Titanium is a very reactive metal: when exposed to an aerated environment, a thin titanium dioxide film, approximately 1.5-10 nm in thickness, is formed. This oxide is usually compact, adherent to the substrate and chemically stable in a variety of environments, and it isresponsible for the excellent corrosion resistance of titanium.

Despite this, titanium suffers corrosion in aggressive environments. Titanium may suffer both uniform corrosion and localized corrosion: crevice and pitting, hydrogen embrittlement, stress-corrosion cracking, fretting corrosion and erosion.

To overcome these potential issues, one possible way is to increase the natural thickness of TiO2 is by surface treatments. Oxidation treatments,specifically anodization, have been considered to tune the TiO2 layer in order to increase itsthickness and to obtain a mostly amorphous phase, with the final aim to increase pure titanium corrosion resistance up to the level of more expensive alloys. Thermal oxidation, chemical oxidation and ion implantation are other possible techniques.

Because of the ease of formation of this protective oxide, corrosion resistance of titanium can be studied by considering the condition under which this oxide is thermodynamically unstable. According to the Pourbaix diagram of titanium in water, titanium is in passive conditions over a wide range of potentials and becomes vulnerable only in strongly oxidizing conditions, where oxide is dissolved,and under strongly reducing conditions, where hydrides are formed. This range is relatively insensitive to chlorides, and for this reason, titanium has an innate resistance in aqueous chloride-containing environments.

When titanium is in a passive condition, due to the thin oxidation of titanium surfaces, corrosion rates equal the passive current density: typical values are lower than 0.02 mm/year. This oxide film growth may manifest itself as a colored surface and very slight weight gain by test coupons. The color acquired from the oxide is due to interference between light rays reflected from the oxide and light rays reflected by the oxide and then reflected from the metal underneath,and for this reason, the resulting color is strongly dependent on film thickness. Due to the strong passive layer, titanium elements are generally designed without any corrosion allowance .

Titanium corrosion resistance is strongly dependent on the resistance of its protective oxide, which can vary as a function of the surrounding environment.