Corrosion Resistance of Implant Alloys in Pseudo Physiological Solution and Role of Alloying Elements in Passive Films

Abstract

The corrosion resistance of implant alloys was investigated by anodic polarization measurements in a pseudo physiological solution. Role of alloying elements in passive film formed on implant alloys by the anodic polarization was also examined with X-ray photoelectron spectroscopy (XPS). Passivity zones of SUS316L stainless steel and Co–Cr alloys are narrow, and a rapid increase in the current density is observed from a low potential as compared to Ti alloys. The passive current density of Ti-15%Zr-4%Nb-2%Ta-0.2%Pd alloy (mass%) is very low. Effects of protein and dissolved oxygen with 90%N2+5%CO2+5%O2 gas bubbling on anodic polarization curves are not detected. The passive film formed on the Ti-6%Al-4%V extra low interstitial alloy consists mainly of TiO2, Al2O3 and small amounts of V oxide. Passive films on the Ti-15%Zr-4%Nb-2%Ta-0.2%Pd and Ti-15%Sn-4%Nb-2%Ta-0.2%Pd alloys consist of TiO2, ZrO2, SnO2, Nb2O5, Ta2O5 and PdO or Pd. XPS spectra from the Co–Cr alloy and SUS316L stainless steel show peaks of Cr2O3, CoO, Fe oxide, Mo oxide, Ni, Co, Fe, Mo and Cr. As Ni, V and Co are strong cytotoxic elements, it was found that biocompatibility of SUS 316L, Co–Cr, Ti-6%Al-4%V ELI alloys become lesser after a long time use in the living body. The thickness of the passive film on Ti alloys is thinner than that of Co–Cr alloy. Passive film formed on the Ti-15%Zr-4%Nb-2%Ta-0.2%Pd alloy is strong and stable.