Phase stability and mechanical properties of the metastable beta Ti alloys containing high oxygen content and various amount of several beta stabilizing elements

Abstract

Metastable beta Ti alloys are considered as perspective materials for the new generation of body implants. Their strength can be substantially improved by addition of interstitial oxygen to fit the requirements for implant materials (strength at least on par with Ti-6Al-4V).

By adding 0.7 wt.% of oxygen, the yield strength of 1000 MPa can be achieved in the beta quenched condition while the ductility of approx. 20% is obtained. The Young's modulus close to that of a bone (10-30 GPa) is preferred to avoid the so-called stress-shielding effect.

To achieve this reduction of Young's modulus, several Ti-Nb-Zr-O based alloys with identical content of O (0.7 %) and various content of Nb, Ta and Zr were produced and studied thoroughly by means of tensile testing, scanning electron microscopy, x-ray diffraction and resonant ultrasound spectroscopy for precise measurement of Young's modulus. It was found, that Young's modulus drops with lower beta phase stability (i.e. lower amount of Nb, Ta, Zr) and e.g.

Ti-29Nb-7Zr-0.7O alloy exhibits Young's modulus of 60 GPa while the yield strength reaches 1000 MPa while simultaneously keeping the elongation around 20%.