Williams, Michael Eric (2008-05). Ab-initio elastic and thermodynamic properties of high-temperature cubic intermetallics at finite temperatures. Master's Thesis. Thesis uri icon

abstract

  • In thiswork we present the development of a method for the prediciton of finite temperature elastic and thermodynamic properties of cubic, non-magnetic unary and binary metals from first principles calculations. Vibrational, electronic and anharmonic contributions to the free energy are accounted for while magnetic effects are neglected. The method involves the construction of a free energy surface in volume/temperature space through the use of quasi-harmonic lattice dynamics. Additional strain energy calculations are performed and fit to the derived thermal expansion to present the temperature dependence of single crystal elastic constants. The methods are developed within the framework of density functional theory, lattice dynamics, and finite elasticity. The model is first developed for FCC aluminum and BCC tungsten which demonstrate the validity of the model as well as some of the limitations arising from the approximations made such as the effects of intrinsic anharmonicity. The same procedure is then applied to the B2 systems NiAl, RuAl and IrAl which are considred for high temperature applications. Overall there is excellent correlation between the calculated properties and experimentally tabulated values. Dynamic methods for the prediction of temperature dependent properties are also introduced and a groundwork is laid for future development of a robust method.
  • In thiswork we present the development of a method for the prediciton of finite temperature
    elastic and thermodynamic properties of cubic, non-magnetic unary and binary metals
    from first principles calculations. Vibrational, electronic and anharmonic contributions to
    the free energy are accounted for while magnetic effects are neglected. The method involves
    the construction of a free energy surface in volume/temperature space through the use of
    quasi-harmonic lattice dynamics. Additional strain energy calculations are performed and
    fit to the derived thermal expansion to present the temperature dependence of single crystal
    elastic constants. The methods are developed within the framework of density functional
    theory, lattice dynamics, and finite elasticity. The model is first developed for FCC aluminum
    and BCC tungsten which demonstrate the validity of the model as well as some of
    the limitations arising from the approximations made such as the effects of intrinsic anharmonicity.
    The same procedure is then applied to the B2 systems NiAl, RuAl and IrAl which
    are considred for high temperature applications. Overall there is excellent correlation between
    the calculated properties and experimentally tabulated values. Dynamic methods for
    the prediction of temperature dependent properties are also introduced and a groundwork
    is laid for future development of a robust method.

publication date

  • May 2008