EFFECT OF SMALL QUANTITY OF OXYGEN AND NI TROGEN ON MECHANICAL-PROPERTIES OF NEW TITANIUM-ALLOYS FOR MEDICAL IMPLANTS

The combined effect of O and N additions on the fatigue properties wit h Ti-15%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 mere investigated by fatigue testing in a physiological saline solution at 310 K. The fatigue test was carried out under the c ondition of a tension to tension mode with a sine wave at a stress rat io of 0.1 and at a frequency of 2 Hz and 10 Hz in Eagle's medium solut ion using an environment cell with 90%N-2 + 5%CO2 + 5%O-2 gas bubbling . Further the effect of human hip joint load profile estimated by anal ysis of forces and actions for human hip joint on the corrosion fatigu e strength were examined. The effect of heat treatment on the mechanic al strength of the new Ti alloys were investigated. As the solution tr eatment temperature increased the ductility of Ti-Zr and Ti-Sn alloys decreased. After solution treatment, the mechanical strength of Ti-Zr and Ti-Sn alloys did not change much as the aging time and the aging t emperature increased. The additions of O and N to the new Ti alloys an d heat treatment substantially increased the ultimate tensile strength to 1000 MPa. Also, the total elongation was more than 10%. The fatigu e strength of Ti-Sn alloy added 0.2%O, 0.005%N and Ti-Zr alloy added 0 .2%O, 0.05%N at 10(8) cycles was 1050 MPa and 950 MPa, respectively. T he effect of frequency on the fatigue strength at 2 Hz and 10 Hz was a lmost similar. Moreover, the fatigue strengths ware almost the same fo r sine wave and human hip joint load profile in both Ti-Zr and Ti-Sn a lloys.