The effect of SMAT-induced grain refinement and dislocations on the corrosion behavior of Ti-25Nb-3Mo-3Zr-2Sn alloy

A nanocrystalline layer, which consists of pure beta phase with high density of dislocations on Ti-25Nb-3Mo-3Zr-2Sn alloy, was fabricated by surface mechanical attrition treatment (SMAT). The corrosion behavior of the as-SMATed sample, together with the solution-treated coarse-grained and 200 degrees C annealed SMATed samples, was investigated by potentiodynamic polarization and electrochemical impedance spectroscope (EIS) techniques in physiological saline and simulated body fluid (SBF) solutions. The results demonstrate that the corrosion resistance of the studied alloy in both of the solutions considerably increased as the grain size decreased from microscale to nanoscale, which is ascribed to the dilution of segregated alloying elements at grain boundaries and the formation of more stable and much thicker passive protection films on the nanograined samples. Although the SMAT-induced grain refinement and dislocations both have positive effects on the corrosion behavior of the studied alloy, our post annealing experimental results indicate that the improved corrosion resistance is mainly due to the grain refinement. (C) 2013 Elsevier B.V. All rights reserved.