Corrosion behavior of thermo-mechanically processed biomedical Ti-29Nb-13Ta-4.6Zr

The effects of thermomechanical processing (TMP) on the corrosion behavior of a titanium based bio-alloy are addressed in the present work. In this regard two distinct temperature regime, i.e. warm compression at two temperatures of 300 and 400 °C along with hot compression at 900 °C, which is above the corresponding β-transus temperature, were contemplated for TMP cycles. The results showed that the corrosion resistant of processed materials was extremely higher than that of as-received one. The electron backscatter diffraction (EBSD) studies characterized two different mechanisms which played important roles in the material corrosion behavior. In the warm worked specimens, the martensite plates were seen at the vicinity of different types of deformation bands. These martensite plates were thought to assist improving the corrosion rate of processed materials through creating a continuous passive surface film. On the contrary, the occurrence of extended dynamic recovery in addition to the partial dynamic recrystallization in the materials processed at 900 °C could raise the intrinsic susceptibility to local attack thereby increasing the corrosion rate. The latter was attributed to the higher dissociation rate of moving dislocations at non-equilibrium serrated grain boundaries (specially at lower strain rate) and higher fraction of high angle grain boundaries (specially at higher strain rate), which could act as preferred sites for corrosion attack initiation.