Calculations for displacive ω-phase transformations in Ti-Al alloys with Nb additions at finite temperature.
J Phys Condens Matter
; 20(46): 465206, 2008 Nov 19.
Article
en En
| MEDLINE
| ID: mdl-21693846
We examine by means of first-principles calculations the bcc-like (bcc: body centered cubic) to ω-like phase transformations in Ti-Al alloys with Nb additions at finite temperature. To simulate the alloy we use different discrete atomic configurations in a six atom unit cell of the stoichiometry Ti(3)Al(2)Nb. Calculated ground state energies show an instability in the ternary Ti(3)Al(2)Nb alloy against the ω structure type atomic displacement. To better understand the role of entropy in the stability/instability of these systems, the first-principles calculations are extended to finite temperature by including various contributions to the free energy. In particular, the vibrational free energy is calculated within a quasiharmonic approximation. It is shown that the bcc structure is stabilized by the contribution of the low energy modes to the lattice entropy against ω type atomic displacements. We find that configurational entropy plays a major role in the ω to B8(2) transformation. Calculated lattice parameters and transition temperatures are found to be in excellent agreement with experiment.
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Base de datos:
MEDLINE
Idioma:
En
Revista:
J Phys Condens Matter
Asunto de la revista:
BIOFISICA
Año:
2008
Tipo del documento:
Article
País de afiliación:
Estados Unidos
Pais de publicación:
Reino Unido