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

Abstract

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.

By adding 0.7 wt.% of oxygen, the yield strength of 1000 MPa can be achieved in the 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 Zr (7 %) and O (0.7 %) and various content of Nb, Ta and Fe were produced and studied thoroughly. It was found, that Young's modulus drops with lower beta phase stability (i.e. lower amount of Nb, Fe, Ta) and e.g.

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