EFFECT OF COMPRESSIVE STRAINING ON CORROSION-RESISTANCE OF A SHAPE-MEMORY NI-TI ALLOY IN RINGERS SOLUTION

The effect of various degrees of deformation was investigated at speci fic locations in the stress-strain curve under compression on the corr osion resistance of a wrought Ni-Ti alloy with a martensite to austeni te 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 resista nce of the annealed material condition was examined after deformation in compression to 11.9, 22.3, and 24.4% strain. Tafel extrapolation an d cyclic polarization tests were used for corrosion characterization o f each alloy condition. It was found that the corrosion current densit y undergoes a significant reduction while the breakdown potential impr oves at increasing strains. In particular, the alloy in the annealed c ondition exhibited breakdown potentials above 1000 mV with current den sities lower than 10 mu A cm(-2) when it was strained to 24.4%. (C) 19 96 John Wiley & Sons, Inc.