Grade 2 titanium is commercially pure titanium. When its surface is exposed to oxygen or moisture, a new corrosion resistant layer of titanium oxide is created. It resists both acids (oxidizing and mildly reducing) and alkali. Usage of Grade 2 titanium fasteners in marine environments is common. Grade 2 titanium fasteners are used for orthopedic and dental implants. Although non-toxic, its chips are extremely flammable.
The advantage of Grade 5 titanium is that it is heat treatable. Although it is more than twice as strong as Grade 2 titanium, its corrosion resistance is not quite as good.
A small addition of palladium is used to create Grade 7 titanium. This addition gives it better corrosion resistance than Grade 2 titanium fasteners in cryogenic and highly acidic environments.