[SY-E12] Diffusivities and atomic mobilities in bcc Ti-Mo-Nb-Ta-Zr alloys
Titanium and its alloys are widely used in biomedical field due to the low elastic modulus comparable to bone as well as high specific strength and high corrosion resistance. β-type (with bcc structure) and near β titanium alloys comprising non-toxic and non-allergic elements have been extensively investigated in the past decades to achieve low Young’s modulus and good mechanical properties. Researchers suggested that Zr, Nb, Ta and Mo are the most desirable alloying elements in β-type bio-Ti alloys which have ability to effectively increase strength and reduce elastic modulus according to electronic structural calculations. Recently, a number of low-modulus biomedical β-titanium alloys have been developed, for example, Ti-29Nb-13Ta-4.6Zr (TNTZ), Ti-24Nb-4Zr-7.9Sn and Ti-8Mo-4Nb-2Zr.
Diffusivities play important roles when we manipulate above phase transformations and control microstructure development. The diffusion paths and phase fractions during homogenization and precipitation are precisely predicted with the help of thermodynamic and kinetic data by means of the Thermo-Calc and DICTRA software [2,3]. The microstructure evolution during heat treatment can be not only statistically explained via the classical nucleation and growth model equipped with accurate diffusivities, but also represented by the phase field modeling allying with diffusion kinetic database of multi- component and multi-phase systems.
In this work, the diffusivities of sub-ternary systems in Ti-Mo-Nb-Ta-Zr were extracted from composition profiles of diffusion couples using Whittle-Green [4] and Hall [5] methods. Based on the experimental results and thermodynamic descriptions, a self-consistent atomic mobility database of bcc Ti-Mo-Nb-Ta-Zr alloys were assessed using DICTRA software. All the kinetic descriptions were further verified by comprehensive comparisons between various model-predicted diffusion properties and the experimental data. The general agreement validates the potential application of the present atomic mobility database to simulate the diffusion in higher orders.
[1] J.-O. Andersson and J. Ågren, J. Appl. Phys. 72 (1992) 1350-1355.
[2] J.-O. Andersson et al., Calphad. 26 (2002) 273-312.
[3] D.P. Whittle and A. Green, Scr. Metall. 8 (1974) 883-884
[4] L.D. Hall, J. Chem. Phys. 21 (1953) 87-89.
Diffusivities play important roles when we manipulate above phase transformations and control microstructure development. The diffusion paths and phase fractions during homogenization and precipitation are precisely predicted with the help of thermodynamic and kinetic data by means of the Thermo-Calc and DICTRA software [2,3]. The microstructure evolution during heat treatment can be not only statistically explained via the classical nucleation and growth model equipped with accurate diffusivities, but also represented by the phase field modeling allying with diffusion kinetic database of multi- component and multi-phase systems.
In this work, the diffusivities of sub-ternary systems in Ti-Mo-Nb-Ta-Zr were extracted from composition profiles of diffusion couples using Whittle-Green [4] and Hall [5] methods. Based on the experimental results and thermodynamic descriptions, a self-consistent atomic mobility database of bcc Ti-Mo-Nb-Ta-Zr alloys were assessed using DICTRA software. All the kinetic descriptions were further verified by comprehensive comparisons between various model-predicted diffusion properties and the experimental data. The general agreement validates the potential application of the present atomic mobility database to simulate the diffusion in higher orders.
[1] J.-O. Andersson and J. Ågren, J. Appl. Phys. 72 (1992) 1350-1355.
[2] J.-O. Andersson et al., Calphad. 26 (2002) 273-312.
[3] D.P. Whittle and A. Green, Scr. Metall. 8 (1974) 883-884
[4] L.D. Hall, J. Chem. Phys. 21 (1953) 87-89.