Effect of Ti on β Structural Stability and Mechanical Properties of Zr-Nb Binary Alloys

Metastable bcc beta-Zr alloys generally have low elastic modulus, magnetic susceptibility, good mechanical properties, corrosion resistance, and biocompatibility, which are ascribed to co-alloying of multiple elements to enhance the structural stability of the bcc-beta phase. This work systematically investigated the effects of Nb and Ti elements on the structural stability of the bcc-beta phase and mechanical properties of Zr-Nb-Ti alloys. Various binary [Zr-Zr-14] (Zr, Nb)(3) alloy compositions were designed by the cluster formula approach, based on which Ti was substituted for the base Zr to form ternary alloys. Alloy rods were prepared by the copper-mold suction-cast method with vacuum protection. The microstructure and mechanical properties of the alloys were characterized using XRD, OM, and TEM etc. The results show that the crystal structures of the Zr-Nb binary alloys could change from hcp-alpha to bcc-beta with increasing Nb content, whereas, the.-phase always coexists with the beta-phase. An appropriate amount of Ti addition can significantly inhibit the precipitation of., resulting in the further improvement of the stability of the beta-phase. The single beta-[Ti-Zr-14]Nb-3 (Zr-17.37Nb-2.98Ti, mass fraction, %) ternary alloy exhibited not only a low elastic modulus of E=57 GPa but also a good tensile property with a high yield strength of sigma(YS)=557 MPa and an elongation of delta=15.5%.