Improved ductility by coupled motion of grain boundaries in nanocrystalline B2-FeCo alloys

[Display omitted] •Our improved potential well reproduced the fundamental properties, especially the APB energies.•The large concentrated stress at GBs ascribed to the poor plastic-deformation compatibility causes the occurrence of microcracks.•The GB migration energy barrier decreases with the decreasing degree of order.•The GB-dominant plasticity can improve the plastic-deformation compatibility and release the concentrated stress at GBs to prevent the generation of microcracks. Embedded-atom method (EAM) potential for the FeCo binary systems has been improved to reproduce the antiphase boundary (APB) energies, crucial to the mechanical properties for ordered alloys. Using the improved potential, we further carried out tensile simulations on nanocrystalline FeCo models to investigate the effect of disordered grain boundaries (GBs) on the intergranular fracture. We found that the large concentrated stress at GBs ascribed to the poor dislocation behavior and plastic-deformation compatibility caused the occurrence of microcracks. As the degree of order at GBs was reduced, the GB motion can be enhanced contributed to the smaller GB migration energy barrier. The GB-dominant plasticity can improve the plastic-deformation compatibility and release the concentrated stress at GBs to prevent the generation of microcracks and intergranular fracture. Collectively, the enhancement of coupled GB motion by disordered GBs opens more pathways to improve the mechanical properties for both nanostructured and conventional polycrystalline alloys with ordered superlattice structures.