The molybdenum-titanium phase diagram evaluated from ab-initio calculations

The design of next generation β-type titanium implants requires detailed knowledge of the relevant stable and metastable phases at temperatures where metallurgical heat treatments can be performed. Recently, a standard specification for surgical implant applications was established for Mo-Ti alloys. However, the thermodynamic properties of this binary system are not well known and two conflicting descriptions of the β-phase stability have been presented in the literature. In this study, we use ab-initio calculations to investigate the Mo-Ti phase diagram. These calculations predict that the β-phase is stable over a wide concentration range, in qualitative agreement with one of the reported phase diagrams. In addition, they predict stoichiometric compounds, stable at temperatures below 3000C, which have not yet been detected by experiments. The resulting solvus, which defines the transition to the β-phase solid solution, therefore occurs at lower temperatures and is more complex than previously anticipated.