EFFECTS OF HEAT-TREATMENT ON MECHANICAL-PROPERTIES AND CORROSION-FATIGUE STRENGTH IN PHYSIOLOGICAL SALINE SOLUTION OF NEW TITANIUM-ALLOYS FOR MEDICAL IMPLANTS

Ti-15mass%Zr-4%Nb-4%Ta-0.2%Pd and Ti-15%Sn-4%Nb-2%Ta-0.2%Pd alloys nor containing V and Al for surgical implantation were cast by plasma ele ctron beam melting. The effect of beat treatment on room temperature s trength and corrosion fatigue strength were investigated by aging trea tment after solution treatment. The alloys were forged in their alpha and alpha + beta regions, and then solution-treated at 953 similar to 1173 K for 3.6 ks. Optimized solution treatment conditions are 1038 K -3.6 ks for Ti-Zr alloy and 1098 K -3.6 ks for Ti-Sn alloy containing 15 similar to 20 vol% of primary alpha phase. After solution treatment under the optimized conditions, aging treatment was carried out at 62 3 similar to 873 K for 600 s similar to 108 ks. Optimized aging condit ions for Ti-Zr and Ti-Sn alloys were at 673 K for 36 ks and at 723 K f or 36 ks, respectively. The room temperature strengths of these soluti on treated and aged alloys were about 30% higher than the annealed all oys. It is revealed by transmission electron microscopic observation t hat, fine alpha phase precipitates in alpha' martensitic matrix are re sponsible for the age hardening. The corrosion fatigue test in a physi ological saline solution was carried out under the condition of a tens ion to tension mode with a sine wave al a stress ratio of 0.1, at a fr equency of 10 Hz in Eagle's MEM+fetal bovine serum solution using an e nvironment cell with 90%N-2+5% CO2+5%O-2 gas bubbling at 310 K. The fa tigue strength at 10(7) cycles in solution-treated and aged Ti-15%Zr-4 %Nb-4%Ta-0.2%Pd and Ti-15%;Sn-4%Nb-2% Ta-0.2%Pd alloys were about 650 MPa and 800 MPa respectively, which were about 20 similar to 30% highe r than those of the annealed alloys.