Mechanical properties and microstructures of beta-type titanium alloy for biomedical applicaitons

Plain and notch fatigue properties of a β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), which was subjected to various thermomechanical treatments, were investigated in order to judge its potential for biomedical applications. Microstructures of TNTZ aged at 723 K for 259.2 ks after cold rolling and those aged at 723 K for 259.2 ks after solution treatment are composed of a precipitated a phase in the β phase. However, microstructures of TNTZ aged at 598 and 673 K for 259.2 ks after cold rolling and aged at 598 K and 673 K for 259.2 ks after solution treatment are composed of a precipitated ω phase, and precipitated α and ω phases in the β phase, respectively. Futher, plain fatigue strengths of TNTZ aged after solution treatment and those of TNTZ aged after cold rolling increase with the aging temperature. In particular, TNTZ aged at 723 K after cold rolling exhibits the highest fatigue strength in both the low- and high-cycle fatigue life regions. Futher, the run-out, which is about 770 MPa, is nearly equal to that of hot-rolled Ti-6A1-4V ELI conducted with aging, which is one of the representative α+β-type titanium alloys for biomedical applications. The notch fatigue strengths of TNTZ aged at stress concentration factors of 2 and 6 decrease by 30% - 40% and 50% - 60%, respectively, as compared with the plain fatigue strengths in the low-cycle fatigue life region. Futher, the notch run-out range from 450 to 490 MPa and from 220 to 300 MPa, respecitvely; an exception to this is TNTZ aged at 598 K after cold rolling, which has a high volume fraction of the ω phase. Single- and multi- fatigue cracks initiate at the bottom of the notch at stress concentration factors of 2 and 6, respectively.