The Effect of Surface Abrasion On the Polarization Behavior or CoCr, Ti-6Al-4V and 316 SS In Pbs at pH7.4 and 2

Abstract: Our laboratory has documented significant and severe corrosion of medical alloys in vivo resulting from the process of mechanically assisted corrosion where the oxide films on these surfaces are abraded (e.g., fretting), and the corrosion rate is significantly increased as a result. In this study, we have performed a simple set of voltage-controlled tests of the current response of alloy surfaces while abrading with 600 grit emory paper in pH 7.4 or pH 2 phosphate buffered saline. Samples of Ti-6Al-4V (ASTM F-136) , Co-Cr-Mo (ASTMF-1537), and 316L SS (ASTM F138) were held at fixed voltages ranging from -1200 mV to +1000 mV (100 mV increment) for 60 s. The sample currents equilibrated without abrasion for 15 s, then from 15 s to 30 s the samples were vigorously abraded with 600 grit sand paper, and from 30 to 60 s the sample was allowed to recover. Data was acquired at 1000 pts per minute and the tests were repeated on three separate samples at each voltage, pH condition. The resting current density, average abrasive current density, and recovery time were all measured as a function of pH and voltage. The results show significant effects of abrasion on current densities in abrasion-polarization plots that are 2 orders of magnitude higher than the at-rest response, that each material exhibited unique ranges of behavior, and that the different pH's mostly affected the cathodic response region. The differences between abraded and resting current densities were voltage and pH dependent with more positive voltages showing greater differences. The time constants for recovery were also a function of pH, voltage and material. These results show the underlying effects of the oxide film on these surfaces and its role in modulating the electrochemical response during mechanical abrasion.