The Effects of Heat Treatment, Surface Condition and Strain On Nickel-Leaching Rates and Corrosion Performance In Nitinol Wires

The effects of heat treatment, surface condition and strain levels on nickel-leaching rates and corrosion performance of nitinol wires were examined. Wires were subjected to three different heat treatments: traditional shape set; aged at low temperature to produce nickel-rich precipitates; and aged at high temperature to dissolve precipitates and annihilate dislocations. Wires from each heat treatment were tested in the as-drawn, chemically etched, and electropolished conditions. Further, wires from each condition were tested at up to eight-percent strain. Nickel leaching rates and changes in open circuit potential were evaluated for the various wire conditions over 60-days in phosphate-buffered saline. Following the 60-day exposure, corrosion performance was assessed for each wire heat treatment, surface, and strain condition using potentiodynamic cyclic polarization testing.