Effect of Thermo-Mechanical Treatments on the Microstructure and Mechanical Properties of the Metastable β-type Ti-35Nb-7Zr-5Ta Alloy

In this work, theoretical composition design and thermo-mechanical treatments were combined in order to improve the mechanical compatibility of a biomedical β-type titanium alloy. By applying a composition design theory, cold rolling and low temperature aging, a metastable β-type Ti-35Nb-7Zr-5Ta (wt%) alloy with an elastic modulus of 47 GPa and a yield strength of 730 MPa was successfully fabricated. This combination of high yield strength and low elastic modulus resulted in enhanced elastic recoverable strain of 1.7%, which is much higher than that of the conventional metallic biomaterials. The microstructure responsible for the much sought-after mechanical properties was observed to be mainly consisted of a homogeneous distribution of nanometer-sized ω- and α-precipitates in a β-phase matrix obtained via cold rolling plus short-time aging at low temperature, i.e. aging at 673 K for 20 min. These precipitates increase the strength of the material by hindering the motion of dislocations while the β-matrix with relatively low content of β-stabilizers gives rise to the observed low elastic modulus. By extending aging time, a higher strength is reached at the expense of an undesirable increasing in elastic modulus.