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

TL;DR

This study uses ab-initio calculations to evaluate the Mo-Ti phase diagram, revealing a wider stability of the eta-phase and predicting new stable compounds, which impacts the design of titanium implants.

Contribution

The paper provides the first ab-initio based phase diagram for Mo-Ti alloys, clarifying eta-phase stability and predicting new compounds not yet observed experimentally.

Findings

eta-phase is stable over a broad concentration range.

Predicted stable compounds below 3000°C.

The solvus occurs at lower temperatures than previously thought.

Abstract

The design of next generation \beta-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 \beta-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 \beta-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 \beta-phase solid solution, therefore occurs at lower temperatures and is more complex than previously anticipated.