The Corrosion Behavior of Nitico High Stiffness Shape Memory Alloys

The development of high stiffness NiTi-based shape memory alloys has attracted much attention recently due to industry driven material performance requirements.  A NiTiCo shape memory alloy has been successfully developed for industry applications, which exhibits higher upper plateau stress (UPS)/lower plateau stress (LPS) compared to binary NiTiNol alloys.  In the present study, the corrosion behavior of the NiTiCo high stiffness shape memory alloy was systematically investigated, including straight annealed wires and generic product like wire-formed stents and a stent design laser-cut from NiTiCo tubing.  The corrosion tests were conducted in phosphate buffered saline (PBS) solution at 37°C per ASTM F 2129.  All samples were electropolished and passivated before corrosion test to represent standard practice of surface finishing.  The rest potential, breakdown potential and re-passivation potentials were compared to binary NiTiNol counterparts.  This study investigated on generic product made from NiTiCo wire and tube to mimic the behavior of engineered medical devices.