CORROSION-RESISTANCE ACID MECHANICAL-PROPERTIES OF NEW TITANIUM-ALLOYS FOR CENTRIFUGALLY CAST DENTAL IMPLANTS

Ti-15 mass%Zr-4%Nb-4%Ta-0.2%Pd-0.2%0-0.05%N and Ti-15%Sn-4%Nb-2%Ta-0.2%Pd-0.2%0 alloys without V and Al elements for surgical implantation were cast by vacuum are-melting in response to recent concerns about the long term safety of Ti-6%Al-4%V extra low interstitial alloy (ASTM standard for surgical implantation). After the alloys were forged in their alpha and alpha+beta regions, specimens of 30 mm in diameter and 13 mm in height were are-melted in an argon gas atmosphere with a titanium casting machine for dental use using a tungsten electrode. The molten alloys were cast into a graphite mold by centrifugal force. The cast microstructures of the Ti-Zr and Ti-Sn alloys consisted of alpha' martensitic structure. To examine the centrifugal alloy properties for dental application, the corrosion resistance and mechanical properties of the alloys were investigated by the anodic polarization in 5 mass%HCl and 1 mass% lactic acid solutions, the measurement micro-Vickers hardness and the tensile test at room temperature. The anodic polarization properties of the Ti-Zr and Ti-Sn alloys cast in a 1% lactic acid solution are almost the same as those of Ti-Zr and Ti-Sn alloys annealed at 973 K for 7.2 ks after alpha+beta forging. A rapid increase in current density resulted from the low potential in a 5%HCl solution in comparison with the annealed Ti-Zr and Ti-Sn alloys. The passive films on the Ti-15%Zr-4%Nb-2%Ta-0.2%Pd and the Ti-15%Sn4%Nb-2%Ta-0.2%Pd alloys in a 1% lactic acid solution consisted of TiO2, ZrO2, SnO2, Nb2O5, Ta2O5 and PdO or Pd as demonstrated by X-ray photoelectron spectroscopy (XPS). Micro-Vickers hardness dose not change from the surface to the central part in castings. The strength of the cast Ti-Zr and Ti-Sn alloys was higher than the annealed Ti-Zr and Ti-Sn alloys. However, the ductility of the cast alloys was lower than the annealed ones.