MECHANICAL-PROPERTIES AND CORROSION-FATIGUE OF NEW TITANIUM-ALLOYS FOR MEDICAL IMPLANTS IN PHYSIOLOGICAL SALINE SOLUTION

The corrosion fatigue and mechanical properties of Ti-15%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 were compared with those of Ti-6%Al-4%V ELI, Ti-6%Al-2%Nb-1%Ta and beta type Ti-15%Mo-5%Zr-3%Al alloys for medical implants by corrosion fatigue testing in a physiological saline solution at 310 K and tensile testing at room temperature. The corrosion fatigue test was carried out under the condition of a tension to tension mode with a sine wave at a stress ratio of 0.1 and at a frequency of 10 Hz in eagle's MEM + bovine serum solution using an environment cell with 90%N-2+ 5%CO2 + 5%O-2 gas bubbling. The titanium alloys annealed at 973 K for 7.2 ks showed an acicular structure containing 15 to 30 vol% elongated beta grains. The effect of alloying elements on ultimate tensile strength could be estimated by the following equation. sigma(uts)/MPa=451+12.9[%Zr]+29.3[%Sn]+6.4[%Nb]+8.4[%Ta]-148.2[%Pd]+531[%O]+1646[%N] The cycle to failure of Ti-15%Sn-4%Nb-2%Ta-0.2%Pd-0.2%O and Ti-15%Zr-4%Nb-4%Ta-0.2%Pd-0.2%0-0.05%N alloys annealed at 973 K for 7.2 hs increased linearly with decreasing applied maximum stress. The fatigue strength at 10(7) cycles in those alloys was about 650 MPa. The fatigue strength at 10(7) cycles in Ti-6%Al-2%Nb-1%Ta alloy was about 750 MPa, and it was higher than that of Ti-6%Al-4%V ELI alloy, i.e. 690 MPa. The fatigue strength of 10(7) cycles in the beta type Ti-15%Mo-5% Zr-3%Al alloy was lower than that of the alpha+beta type alloys. Dimple and striation formed by corrosion fatigue testing were seen in the fractured surface of the alpha+beta type alloys, while a river pattern was seen in fatigue surface of the beta type alloy.