Effects of solute and vacancy segregation on antiphase boundary migration in stoichiometric and Al-rich Fe3Al: A phase-field simulation study

Effects of segregation of solute atoms and vacancies on migration of antiphase boundaries (APBs) in stoichiometric (Fe-25 at%Al) and Al-rich (Fe-28 at%Al) Fe3Al at 673 K have been studied using a phase-field method in which local vacancy concentration is taken into account [Koizumi Y, Allen SM, Minamino Y. Acta Mater 2008;56:5861, ibid. 2009;57:3039]. Boundary mobility (M) of APBs having different phase-shift vectors of a/4<111> and a/2<100> (hereafter denoted as B2-APB and D03-APB, respectively) was evaluated by measuring the boundary velocity of shrinking circular APBs. Similar effects of the segregation on the migration of B2-APBs were observed in both compositions. Vacancies segregated and Al-atoms were depleted at B2-APBs in both compositions. Vacancy concentration at B2-APBs was up to 80% higher than that in the bulk. As a result, the migration of B2-APBs was greatly enhanced by the vacancy segregation. In contrast, the segregation to D03-APBs showed a marked composition dependence. Vacancies were depleted and Al-atoms segregated at D03-APBs in the Al-rich Fe3Al, whereas vacancies segregated and Al-atoms were depleted at D03-APB in the stoichiometric Fe3Al. The Al segregation in the Al-rich Fe3Al decreased M of D03-APBs much more significantly than the Al-depletion in the stoichiometric Fe3Al. As the APDs shrank, D03-APBs broke away from the segregation atmospheres and the M increased rapidly in both compositions. A greater increase in the M due to the breakaway was observed in the Al-rich Fe3Al than in Fe3Al with the stoichiometric composition.