US Patent 7101391 Primarily niobium stent

In a process of fabricating a stent composed primarily of niobium alloyed with a trace amount of zirconium, tantalum, or titanium for hardening, the stent is annealed under vacuum in a substantially oxygen-free environment. The vacuum is preferably maintained at pressure less than 10−4 millibars, oxygen-content less than about 80 parts per million, and the annealing temperature exceeds 400° C. for at least one hour, and is preferably kept in a range from about 1100–1200° C. for several hours. This may be followed by applying a surface layer of oxide, such as iridium oxide, with a thickness of 299–300 nm to the stent.