Influence of Nb Addition on α and ω Phase Stability and on Mechanical Properties in the Ti-12Mo-xNb Stoichiometric System

Metastable beta-Ti alloys have become one of the most attractive implant materials due to their high biocorrosion resistance, biocompatibility, and mechanical properties, including lower Young's modulus values. Mechanical properties of these alloys are strongly dependent on the final microstructure, which is controlled by thermomechanical treatment processing, in particular the Young's modulus and hardness. The aim of this work was to analyze the influence of phase precipitations in heat-treated Ti-12Mo-xNb (x = 0, 3, 8, 13, 17, and 20) alloys. The alloys were prepared via arc melting and treated at 950 degrees C/1 h, and then quenched in water. The microstructures were analyzed by optical microscopy, transmission electron microscopy, and X-ray diffraction. Mechanical properties were based on Vickers microhardness tests and Young's modulus measurements. Microstructural characterization showed that alpha '' and omega stability is a function of Nb content for the Ti-12Mo base alloy. Nb addition resulted in the suppression of the alpha '' phase and decrease in the omega phase volume fraction. Although the omega phase decreased with higher Nb contents, omega particles with ellipsoidal morphology were still observed in the Ti-12Mo-20Nb alloy. The alpha '' phase suppression by Nb addition caused a marked increase in the Young's modulus, which decreased back to lower values with higher Nb concentrations. On other hand, the decrease in the omega phase continuously reduced alloy hardness. The study of the effect of chemical composition in controlling the volume fraction of these phases is an important step for the development of beta-Ti alloys with functional properties.

Automated summary

This study analyzed the influence of phase precipitations on the microstructure and mechanical properties of heat-treated Ti-12Mo-xNb alloys. The results showed that the addition of Nb suppressed the formation of the alpha '' phase, but a small amount of omega phase was still observed. The addition of Nb increased the Young's modulus, while the decrease in the omega phase reduced the hardness of the alloy.