Thermal Stabilization of the HCP Phase in Titanium

Abstract

We have used a tight-binding model that is fit to first-principles electronic-structure calculations for titanium to calculate quasi-harmonic phonons and the Gibbs free energy of the hexagonal close-packed (hcp) and omega crystal structures. We show that the true zero-temperature ground-state is the omega structure, although this has never been observed experimentally at normal pressure, and that it is the entropy from the thermal population of phonon states which stabilizes the hcp structure at room temperature. We present the first completely theoretical prediction of the temperature- and pressure-dependence of the hcp-omega phase transformation and show that it is in good agreement with experiment. The quasi-harmonic approximation fails to adequately treat the bcc phase because the zero-temperature phonons of this structure are not all stable.

References in corpus (5)

• Applications of a tight-binding total energy method for transition and noble metals: Elastic Constants, Vacancies, and Surfaces of Monatomic Metals
• A New Mechanism for the Alpha to Omega Martensitic Transformation in Pure Titanium
• Tight-binding study of high-pressure phase transitions in titanium: alpha to omega and beyond
• First-Principles-Based Thermodynamic Description of Solid Copper Using the Tight-Binding Approach
• Block-Diagonalization and f-electron Effects in Tight-Binding Theory

Cited by in corpus (5)

• Impurities block the alpha to omega martensitic transformation in titanium
• Classical potential describes martensitic phase transformations between the $\alpha$, $\beta$ and $\omega$ titanium phases
• An Empirical Tight-Binding Model for Titanium Phase Transformations
• Density functional theory study of the α --> ω martensitic transformation in titanium induced by hydrostatic pressure
• Phase transitions in titanium with an analytic bond-order potential