The Effect of Metal Texture on Depassivation-repassivation Behavior of Iron in Borate Buffer Solution Investigated by Micro-indentation

Abstract

The effects of grain orientation and cold-rolling on the depassivation-repassivation behavior of polycrystalline irons were examined in pH8.4 borate buffer solution using in-situ micro-indentation technique. The depassivation rate on the passive iron surface during the downward drive of the indenter (penetration of an indenter tip into iron surface) depended on the grain orientation; the highest rate was obtained on {100} surface, on which a possible main slip plane of {110} was normal to the surface. In contrast, the total electric charge required for repassivation during the downward and subsequent upward drives was not influenced by the grain orientation. The electric charge for repassivation was strongly influenced by the rolling reduction that changed the dislocation density at the specimen surface. There was a linear correlation between the electric charge normalized by residual dent area and the square root of the dislocation density.