Effects of solute and vacancy segregation on migration of a/4<1 1 1> and a/2<1 0 0> antiphase boundaries in Fe3Al

The effects of segregation of solute atoms and vacancies on migration of a/4<1 1 1> and a/2<1 0 0> antiphase domain boundaries (APDBs) in stoichiometric Fe3Al at various temperatures are studied using a phase-field model [Koizumi Y, Allen SM, Minamino Y, Acta Mater 2008;56:5861] based on the Bragg-Williams approximation and kinetic parameters determined from experimental data. Boundary mobilities (M) were measured from the boundary velocity of shrinking circular antiphase domains (APDs). In the case of a/4<1 1 1> APDBs, solute atmospheres follow the APDB until the APD vanishes by shrinking to zero radius, and therefore the Ms are always smaller than the intrinsic boundary mobilities because of the solute-drag effect. The M of a/4<1 1 1> APDBs can be enhanced by up to 60% by vacancy segregation. On the other hand, the M of a/2<1 0 0> APDBs is enhanced by only a few per cent. The a/2<1 0 0> APDBs are observed to break away from the solute atmosphere during as the circular ABDBs shrink. The M increases by up to 40% associated with the breakaway, and becomes equal to the intrinsic boundary mobilities even though slight depletion and segregation of Al atoms remain ahead and behind the migrating boundary, respectively.