Passivity Breakdown and Repassivation on TiNi During Rapid Straining Accompanying Martensitic Phase Transformation

Abstract

Passive film breakdown and repassivation during rapid deformation of Ni-Ti shape memory alloy were electrochemically characterized using a rapid straining electrode technique. A ribbon shape tensile specimen of Ni-50.1Ti alloy was elongated under potentio-static condition in simulated body fluid. Deformation induced mechanical breakdown of surface film to expose newly created surface resulting in a rapid transient of electrochemical current. Namely, anodic current increased, then decreased due to repassivation. Slight current increase during elastic elongation was followed by a rapid increase in current during martensitic deformation, which may induce surface nanoscopic protrusion and collapse, rapid increase in anodic current was observed. It is noticeable that rapid shrinking by reverse martensitic transformation also arose current increase due to surface film breakdown.

Breakdown of Passive Films and Repassivation of Ti-6Al-4 V Alloy with Rapid Elongation in Simulated Body Fluid including Osteoblast-like Cells

“…Since both dissolution and repassivation can occur in the initial period of the breakdown of passive films, it is necessary to deform the sample rapidly in order to reveal metal dissolution and repassivation separately. Therefore, the rapid straining electrode test 25 was adopted in this study. In the experiment, the samples were elongated very rapidly and the change in anodic current was observed.…”