Yoshimitsu Okazaki1, Kenji Kyo2,Yoshimasa Ito3 and Tetsuya Tateishi1
1Mechanical Engineering Laboratory, Agency of Industrial Science and Technology, Ministry of International Trade and Industry, Tsukuba, Ibaraki
Ti-15 mass%Zr-4%Nb-4%Ta-0.2%Pd-0.2%O-0.05%N and Ti-15%Sn-4%Nb-2%Ta-0.2%Pd-0.2%O alloys without V and Al elements for surgical implantation were cast by vacuum arc-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 α and α+β regions, specimens of 30 mm in diameter and 13 mm in height were arc-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 α′ 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 α+β 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%Sn-4%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.
(Received February 15, 1995)
titanium alloy, dental implant, centrifugal casting, corrosion resistance, microstructure, micro-Vickers hardness, mechanical properties
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