Atomistic Simulation of Loading Direction-Dependent Brittle-to-Ductile Transition in a ⟨110⟩-Oriented B2-FeAl Nanowire Under Bending.

Molecular dynamics simulation was employed to investigate the effect of loading direction on the bending behavior of a B2-FeAl nanowire. The simulations were carried out with different loading directions of [001], [112], [111] and [110] at 300 K. The results show that the FeAl nanowire yields by nucleation of dislocations in all cases, which is independent of the loading direction. However, various loading directions result in different mechanical responses and failure mechanisms. Under [001]- and [112]-bending, the nanowire fails in a brittle manner, whereas changing the loading direction to [111] and [110] directions produces significant plastic deformation with large bending curvature. The brittle-to-ductile transition with respect to loading directions is related to the dislocation characteristics and their cross-slip propensity. Dislocation analysis reveals that [001]- and [112]-bending generate edge-dominant dislocations with limited capability of cross-slip, thereby resulting in stress concentration and subsequent brittle fracture, whereas [111]- and [110]-bending deformation is mediated by slip of dislocations with predominant screw characteristics, whose cross-slip process effectively relaxes stress localizations and sustains uniform plastic deformation. Moreover, a physical model incorporating bending-induced geometric constraints is established to quantify the evolution of dislocation characteristics with respect to loading directions, providing an efficient theoretical framework to rationalize the bending plastic anisotropy of the nanowire.