Thermodynamic description and phase selection for the Mo–Ti–Zr biomedical alloys

Thermodynamic information of the Mo–Ti–Zr ternary system is extremely useful to provide guidance for biomedical alloy development. In the present work, the experimental phase diagram data available from the literature were critically reviewed, and a thermodynamic modeling of the Mo–Ti–Zr system was performed using the CALPHAD (CALculation of PHAse Diagram) approach. The solution phases including liquid, bcc_A2 (β) and hcp_A3 (α) were modelled by the substitutional solution model, and the laves_C15 phase was modelled using a two sublattice model. A set of self-consistent thermodynamic parameters was developed. Comprehensive comparisons between the calculated and measured phase diagrams demonstrate that the experimental information is satisfactorily accounted for by the present thermodynamic modeling. The discrepancies between the calculated and measured phase equilibria have been well explained in this work. With regard to the β phase, the miscibility gap and related phase relations are well described by the present calculation. The liquidus projection and Scheil solidification simulation were generated using the present thermodynamic parameters. The presently calculated phase diagrams of the Mo–Ti–Zr alloys can be used to guide the development of Mo–Ti–Zr biomedical alloys. Based on the present calculations, two guidelines were formulated to avoid the formation of laves phase in these frequently studied Mo–Ti–Zr biomedical alloys.