The effect of segregation and partial order on the thermodynamics of (1 1 1) antiphase boundaries in Ni₃Al

Thermodynamic properties of thermal and a-thermal (1 1 1) antiphase boundaries (APB) in Ni₃Al are computed from first-principles. The effect of off-stoichiometry, partial disordering and segregation are evaluated and a rough estimate of the vibrational contribution to the antiphase boundary energy is given. Although the vibrational effect is found to be small, the configurational effects are large, so that at non-zero temperature and in off-stoichiometric Ni₃Al the antiphase boundary energy (APBE) may be only half of that in perfectly ordered stoichiometric Ni₃Al at zero temperature. This result points to a discrepancy between electronic structure calculations and experimental measurements.