Effect Of In-Situ Deformation On The Corrosion Behavior Of Nitinol Wires

The corrosion behaviors of NiTiNol alloys have attracted much attention due to the wide applications in medical devices.  Usually, the corrosion behavior was conducted on produced medical devices in static conditions.  However, the implanted devices have to bear cyclic loadings for a long period of time.  So, there is a discrepancy between the real applications and the test conditions.  The present study is intended to mimic the effect of in-situ deformation on the corrosion behavior of NiTiNol wires. To explore this issue, NiTiNol wires were straight annealed and surface treated using standard processes for medical devices.  After that, different strains were introduced to the straight wires and the corrosion tests were conducted in the deformed conditions in phosphate buffered saline (PBS) solution at 37°C per ASTM F 2129-08.  The second test is trying to mimic the pulsatile cycling, where the straight wires were in-situ cycled with a 2.5±0.5% strain at 1 Hz frequency during the corrosion test.  In both cases, the occurrence of pitting lower than 800 mV increases significantly compared to the static testing conditions.  This study will shed some light on how to apply the in-vitro tested data to the in-vivo conditions.