## Abstract

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.

Original language | English |
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Article number | 465206 |

Journal | Journal of Physics Condensed Matter |

Volume | 20 |

Issue number | 46 |

DOIs | |

State | Published - Nov 19 2008 |