The thermodynamic properties of thermal and athermal (111) antiphase boundaries were deduced from first principles. The effects of non-stoichiometry, partial disordering and segregation were evaluated and a rough estimate was given of the vibrational contribution to the antiphase boundary energy. Although the vibrational effect was small, the configurational effects were large so that, at non-zero temperatures in off-stoichiometric material, the antiphase boundary energy could be reduced to half of that the perfectly ordered stoichiometric material at zero temperature. The calculations of the vibrational density of states revealed that the most significant contributions arose from the optical branches, and that the acoustic contributions were negligible. The antiphase boundary vibrational free energy was well-represented by the entropy term alone, but the vibrational entropy was much smaller and was of opposite sign to that of the configurational entropy that was associated with off-stoichiometry, partial disorder and segregation. It was concluded that electronic structure calculations for perfectly ordered antiphase boundaries did not agree well with experimental data. Current calculations indicated that segregation at antiphase boundaries could explain the energy differences between thermal and athermal antiphase boundaries. The pinning effect, which resulted from this difference, was found to be a temperature-independent linear function of the deviation from stoichiometry. From the compositional dependence of the geometrical, non-segregated and equilibrium antiphase boundary energies, it was deduced that, the greater the diffusion that occurred, the more the antiphase boundary energy was reduced by off-stoichiometric defects.

A Study of the Thermodynamics of Segregation and Partial Order at (111) Antiphase Boundaries in Ni3Al. Sluiter, M., Kawazoe, Y.: Philosophical Magazine A, 1998, 78[6], 1353-64