Aging behavior of the Ti-29Nb-13Ta-4.6Zr new beta alloy for medical implants

The aging behavior of the Ti-29Nb-13Ta-4.6Zr alloy quenched from 1033 K was investigated by employing electrical resistivity (rho) and Vickers hardness (HV) measurements, optical microscopy (OM), and X-ray diffraction (XRD). Upon aging at 573 K, the rho value at room- and liquid-nitrogen temperatures initially increased to 120 and 30 ks, respectively, and decreased with continued aging time. The HV value started to increase from 0.06 ks and the isothermal omega phase was identified at 300 ks of aging by XRD. On aging at 773 K, an incubation period of 6 ks was observed for the rho change at both temperatures, following which rho decreased. An incubation period for the HV change was extended up to 12 ks, and then HV increased. Precipitated alpha was observed and identified by OM and XRD, respectively, whereas no reflections of isothermal omega phase were identified during the whole aging time at 773 K. The upper-limit temperature of isothermal omega precipitation is situated at around 673 K.