EFFECT OF ALLOYING ELEMENTS ON ANODIC POLARIZATION PROPERTIES OF TITANIUM-ALLOYS IN ACID-SOLUTIONS

The effect of Zr, Sn, Nb, Ta, Pd, N and 0 on the corrosion resistance of titanium alloys for medical implants was investigated by measuring the anodic polarization curves at 310 K in 5 mass% H2SO4 and 5%HCI solutions deaerated by high-purity N2 gas bubbling. The critical current density for passivation (I(c)) and passive current density at 0.6 V versus SCE of the titanium alloys markedly decreased with increasing Zr, Nb, Ta, and Pd contents in the range from 5 to 20, 4 to 8, 2 to 4 and 0 to 0.2%, respectively, although Sn had an adverse effect in the range from 10 to 20 mass%. The effect of N and O on I(c) was undetected. The log (I(c)) value decreased linearly with increasing bond order (B(o)BAR) value representing the covalent bond strength between Ti and the alloying elements. The passive film formed on Ti-15%Zr-4%Nb-2%Ta-0.2%Pd alloy in the 5% H2SO4 solution consisted mainly of TiO2, ZrO2, Nb2O5 and Ta2O5, as demonstrated by the electron spectroscopy for chemical analysis (ESCA). The anodic polarization properties of Ti-15%Zr-4%Nb-2%Ta-0.2%Pd and Ti-15%Sn-4%Nb-2%Ta-0.2%Pd alloys were superior to those of the Ti-6%Al-4%V extra low interstitial alloy and SUS316L stainless steel.