Thermodynamic evaluation of the phase equilibria and glass-forming ability of the Ti?Be system |
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Authors: | Tatsuya Tokunaga Hiroshi Ohtani Mitsuhiro Hasebe |
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Affiliation: | (1) Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Sensui-cho 1-1, Tobata-ku, 804-8550 Kitakyushu, Japan;(2) Department of Materials Science and Engineering, Kyushu Institute of Technology, Sensui-cho 1-1, Tobata-ku, 804-8550 Kitakyushu, Japan |
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Abstract: | The glass-forming ability of Ti−Be alloys is of great interest. Experimental and theoretical evaluations of the glass-forming
ability of this binary alloy show that the formation of a metastable TiBe phase with a CsCl-type B2 structure controls the
glass-forming ability in this system. However, there is no information on the thermochemical properties of metastable TiBe
for the quantitative evaluation of the glass-forming ability using Davies-Uhlmann kinetic formulations. We have carried out
a thermodynamic analysis using experimental phase diagram data and the energy of formation of the stoichiometric compounds
from ab initio calculations. Furthermore, the Gibbs energy of formation for the body-centered cubic (bcc) phase was evaluated
over the entire composition range by applying the cluster expansion method (CEM) to the total energy of some bcc-based ordered
structures obtained from ab initio calculations. For the bcc phase, the two-sublattice formalism, (Ti, Be)0.5(Ti,Be)0.5, was adopted to describe the A2/B2 transformation. A good agreement between the calculated values and experimental phase
equilibria was obtained. Evaluation of the glass-forming ability was also attempted utilizing the thermodynamic quantities
obtained from the phase diagram assessment. The calculated glass-forming ability agrees well with the experimental results.
This paper was presented at the International Symposium on User Aspects of Phase Diagrams, Materials Solutions Conference
and Exposition. Columbus, Ohio, 18–20 October, 2004. |
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Keywords: | ab initio calculations CALPHAD entropy of fusion glass-forming ability metastable phase equilibria titanium-beryllium |
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