Effect of copper on the localized corrosion resistance of Ni-Ti shape memory alloy.

An electrochemical study aiming at the evaluation of corrosion parameters using potentiodynamic and potentiostatic techniques ("scratch" and modified ASTM F746) was conducted in 0.9% NaCl on wires from equiatomic Ni-Ti and ternary Ni44Ti51Cu5 superelastic alloys with Ti90Mo10 as a reference material. The results obtained using potentiostatic tests, that simulate better the behavior of material in service conditions than potentiodynamic ones, indicate that both Ni-Ti and Ni-Ti-Cu wires exhibit low corrosion potentials (approximately 50-150 mV versus SCE) inferior to that of Ti-Mo alloy. The latter proved to be immune to localized corrosion attacks up to 800 mV.