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

• Main Authors: David Holec, Neda Abdoshahi, Svea Mayer, Helmut Clemens
• Format: Article
• Language: English
• Published: MDPI AG 2019-04-01
• Series: Materials
• Subjects: thermal expansion; titanium aluminides; thermodynamic properties; ab initio calculations; quasi-harmonic approximation
• Online Access: https://www.mdpi.com/1996-1944/12/8/1292

Anisotropic thermal expansion coefficients of tetragonal <inline-formula> <math display="inline"> <semantics> <mi>&#947;</mi> </semantics> </math> </inline-formula>-TiAl and hexagonal <inline-formula> <math display="inline"> <semantics> <msub> <mi>&#945;</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula>-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 <inline-formula> <math display="inline"> <semantics> <mi>&#947;</mi> </semantics> </math> </inline-formula>-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 <inline-formula> <math display="inline"> <semantics> <msub> <mi>&#945;</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula>-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.