Corrosion behavior of cast titanium with reduced surface reaction layer made by a face-coating method.

This study characterized the corrosion behavior of cast CP titanium made with a face-coating method. Wax patterns were coated with oxide slurry of Y(2)O(3) or ZrO(2) before investing with a MgO-based investment. Three surface preparations were tested: ground, sandblasted, and as-cast. Uncoated castings served as controls. Sixteen-hour open circuit potential (OCP) measurement, linear polarization and potentiodynamic cathodic polarization were performed in an aerated modified Tani-Zucchi synthetic saliva at 37 degrees C. Anodic polarization was conducted in the same deaerated medium. Polarization resistance (R(p)) and Tafel slopes were determined. Corrosion current density was calculated for each specimen. Results (n=4) were subjected to nonparametric statistical analysis (alpha=0.05). Cross sections of cast specimens were examined by optical microscopy. Energy dispersive spectroscopy (EDS) spot analysis was performed at various depths below the surface. The OCP stabilized within several hours for all the specimens. Apparent differences in anodic polarization behavior were observed among the different surfaces. A distinctive wide passive region followed by breakdown was seen on specimens with ground and sandblasted surfaces. There were no significant differences in the corrosion resistance among the control and the two face-coating groups for each group. The Mann-Whitney test showed significantly lower OCP and higher R(p) values for ground surfaces. The surface condition significantly affected the corrosion behavior more than the face coating methods. In most cases, specimens with as-cast surfaces exhibited the least corrosion resistance during the potentiodynamic anodic polarization.