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

Abstract

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 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. In the Mo-Ti-Zr system, there is no ternary compound. A set of self-consistent thermodynamic parameters were developed. Comprehensive comparisons between the calculated and measured phase diagrams suggest that the experimental information is satisfactorily accounted for by the present thermodynamic modelling. 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 in the biomedical field. Based on the calculations in the present work, two guidelines were formulated to avoid the laves phase formation in these frequently studied Mo-Ti-Zr biomedical alloys.