Effects of Solute and Vacancy Segregation on Migration of a/4<111> and a/2<100> Antiphase Boundaries in Fe₃Al

Abstract

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.