Effect of compressive straining on corrosion resistance of a shape memory Ni-Ti alloy in Ringer's solution.

The effect of various degrees of deformation was investigated at specific locations in the stress-strain curve under compression on the corrosion resistance of a wrought Ni-Ti alloy with a martensite to austenite transformation peak of 110 degrees C. Two metallurgical conditions were evaluated: 30% cold drawn and annealed at 900 degrees C for 1 h. The cold drawn material was tested for corrosion resistance after 5.8, 7.4, 12.2, and 24.5% applied strain. Similarly, the corrosion resistance of the annealed material condition was examined after deformation in compression to 11.9, 22.3, and 24.4% strain. Tafel extrapolation and cyclic polarization tests were used for corrosion characterization of each alloy condition. It was found that the corrosion current density undergoes a significant reduction while the breakdown potential improves at increasing strains. In particular, the alloy in the annealed condition exhibited breakdown potentials above 1000 mV with current densities lower than 10 microA cm-2 when it was strained to 24.4%.