Titanium Alloys.

Titanium alloys are high in cost and difficult to form and fabricate. Many of the alloys are, however, essentially immune to corrosion in a wide variety of environments.

General Corrosion Performance.

Titanium alloys are essentially resistance to general corrosion in most environments at ambient temperature. They are essentially immune to crevice attack and pitting. At elevated temperatures they can be subject to pitting and crevice corrosion in some environments.

Stress Corrosion Cracking.

Some of the titanium alloys are subject to stress corrosion cracking. The commercially pure (CP) alloys and Alloy 6Al-4V are the most commonly used alloys and are resistant to stress corrosion cracking in most environments. Use of these alloys is recommended unless higher strength is specifically required. Other alloys may be resistance to stress corrosion cracking but must be evaluated for each specific application.

Other Alloys and Materials.

Several materials that are either effectively immune to corrosion in many environments or have other unique properties are available for use in special applications.

Cobalt Alloys.

Stellite 6 is a cobalt based alloy that is widely used for a combination of abrasion and corrosion resistance. It is difficult to form and fabricate but can be used when its relatively high yield strength (90 ksi), abrasion resistance, and immunity to corrosion are required. MP-35N is another cobalt based alloy that is widely used as an aerospace fastener material. Its combination of extremely high yield strength (285 ksi) and immunity to corrosion are unique. The potential of cobalt alloys are cathodic to most other metals.

Noble Metals.

Gold and platinum are essentially inert in most environments. Gold is sometimes used as a plating on copper alloys to improve electrical contact resistance.  Platinum is primarily used as an anode material for impressed current cathodic protection. It is either used as wire anodes or is bonded to titanium or niobium supports. Platinum and gold are cathodic to most other metals.

Lead Alloys.

Lead and lead alloys corrode uniformly at a low rate in many environments where the protective film of corrosion products formed on their surface is insoluble. However, in the presence of nitrates, acetates, or chlorides, lead alloys can corrode non-uniformly as the corrosion products formed are not protective. Lead-tin solder corrodes in a similar manner.