Effects of Mo equivalent on the phase constituent, microstructure and compressive mechanical properties of Ti–Nb–Mo–Ta alloys prepared by powder metallurgy

The Ti-(0–30)Nb-(2–11)Mo-3.5Ta (wt.%) alloys with the composition interval of 5.0 wt.% for Nb and 3.0 wt.% for Mo were prepared by hot isostatic pressing. The Ti–Nb–Mo–Ta alloys with high compressive strength and favorable ductility were obtained, which enabled the alloys to be used as novel structural or biomedical materials. The phase constituent, microstructure, and compressive properties were investigated. Although the compressive yield strength and the strain at failure showed different correlations to the Nb and Mo content, respectively, the two mechanical property parameters both showed distinctly monotonic correlations to the Mo equivalent. With the increasing Mo equivalent, the content of the α phase decreased, while that of the β phase increased. Simultaneously, the yield strength of the Ti–Nb–Mo–Ta alloys decreased, while the strain at failure increased. Quantitative analyses were then implemented on the grain refinement strengthening, the second-phase strengthening of the α phase, and the solid solution strengthening of the Nb and Mo atoms. After comparing the separate contributions of the above determining factors, it was confirmed that the second-phase strengthening was the dominating mechanism for improving the mechanical properties of the powder metallurgic Ti–Nb–Mo–Ta alloys.