Thermal Expansion and Other Thermodynamic Properties of <i>α</i>₂-Ti₃Al and <i>γ</i>-TiAl Intermetallic Phases from First Principles Methods

Abstract

Anisotropic thermal expansion coefficients of tetragonal γ -TiAl and hexagonal α 2 -Ti3Al phases were calculated using first principles methods. Two approaches with different computational costs and degrees of freedom were proposed. The predicted values were compared with available experimental data showing that for γ -TiAl, the more computational demanding method with decoupled impact of volume and temperature effects on the cell shape leads to significantly better results than that with only ground-state optimised unit cell geometry. In the case of the α 2 -Ti3Al phase, both approaches yielded comparable results. Additionally, heat capacity and bulk modulus were evaluated as functions of temperature for both phases, and were fitted to provide an analytical formula which can be further used.

Keywords

• thermal expansion
• titanium aluminides
• thermodynamic properties
• ab initio calculations
• quasi-harmonic approximation