In vitro corrosion of Ti-6Al-4V and type 316L stainless steel when galvanically coupled with carbon.

In vitro corrosion experiments were conducted employing potentiostatic polarization techniques, a saline environment and candidate biomaterial alloy/carbon combinations. Corrosion currents and potentials of carbon/metal couples were predicted by mixed-potential theory utilizing the polarization curves generated. The alloys examined were annealed ELI grade Ti-6A1-4V and cold-worked 316L stainless steel while the types of carbon examined were LTI pyrolytic carbon and vapor-deposited carbon. It was determined that galvanic couples of carbon to cold-worked 316L stainless steel with carbon/metal area ratios of 10:1 to 100:1 produced coupled corrosion potentials in the range of the observed breakdown potential of the stainless steel. It was therefore predicted that localized corrosion in the form of pitting could occur on the cold-worked stainless steel when coupled to carbon with area ratios of 10:1 or greater. The titanium alloy did not exhibit a breakdown potential up to a potential of 1.2 V. Therefore, accelerated corrosion was not predicted for the titanium alloy to carbon galvanic couples under these experimental conditions. Direct carbon/alloy coupling experiments were conducted to verify the corrosion currents and potentials predicted from mixed-potential theory and polarization curve analysis. The experimental and theoretical values showed good agreement.