The Electrochemical Characters Of Metastable Pitting Behavior Of NiTi Alloy

Potentiostatic and potentiodynamic polarization methods were employed to study the behavior of metastable pitting on NiTi alloy in PBS. This study contained the distribution of Em and Eb research; influence research of Cl" concentration, temperature and electode to metastable characters; influence research of electode, Cl" concentration, suface roughness and pH value to the impedence; and also studied the metastable pitting parameter of 304 stainless steel, such as Em, Eb, number, current, growth speed of metastable pitting, to compare with NiTi alloy's for the internal reasons of NiTi alloy metastable pitting.With the growth of electrode and Cl- concentration, the Em, Eb, number, peak current of the NiTi alloy reflected a diminish trend. But when the temperature went up, the number of metastable pitting had decreased.The electrode went up, the impedence of NiTi alloy went down. But when the potential had come across the Eb, there was Warburg impedence on the impendence curves. Rough suface was better for holes growing. Either in acid solution or in alkai liquid, the passivation capacity of NiTi alloy had weakened. Metastable pitting easily occurred along the direction of nick.The metastable pitting life of NiTi alloy diminished, while potential enhanced. Generally speaking, metastable I and k value were small, and there was no linear relationship between the two. The distribution of I and k value contented a normal distribution.The passivation and anticorrosion capacity of NiTi alloy were much better than 304 stainless steel's. During the passivation area of 304 steel, the electrode influence to the steel were bigger than NiTi alloy. Under high potential, plenty of metastable pitting were found on the suface of NiTi alloy and could repassivated, while the metastable pitting tent tobecome stable pitting.