Abstract
Radiopaque implantable structures (e.g., stents) formed of cobalt-based alloys that comprise cobalt, chromium, tungsten, nickel, and platinum or another another metal having an atomic number or density greater than that of cobalt for increased radiopacity. In particular, processes are described for removing precipitate inclusions (e.g., tungsten rich precipitates) that render the alloy otherwise unsuitable for use in formation of a stent or similar implantable structure. The alloy with such precipitate inclusions can be heat treated within a narrow temperature range of about 1250° C. (e.g., 1225° C. to 1275° C.) for a time period in a narrow range of about 30 minutes (e.g., 20 to 40 minutes), to remove such precipitate inclusions. Higher temperatures and/or longer treatment times surprisingly do not resolve the precipitate inclusions, but treatment at about 1250° C. for about 30 minutes substantially removes the precipitates, resulting in a substantially homogenous structure suitable for use as a stent.