Interaction of an edge dislocation with voids in α-iron modelled with different interatomic potentials

Atomic processes and strengthening effects due to interaction between edge dislocations and voids in α-iron have been investigated by means of molecular dynamics with a recently developed interatomic potential (Ackland et al 2004 J. Phys.: Condens. Matter 16 S2629) and compared with those obtained earlier with an older potential (Ackland et al 1997 Phil. Mag. A 75 713). Differences between the interactions for the two models are insignificant at temperature T>=100 K, thereby confirming the validity of the previous results. In particular, voids are relatively strong obstacles because for large voids and/or low temperature, the initially straight edge dislocation is pulled into screw orientation before it breaks away at the critical shear stress, τ_c. Differences between the core structures and glide planes of the 1/2 \langle 111\rangle

screw dislocation for the two potentials do not affect τ_c in this temperature range. The only significant difference between the dislocation-void interactions in the two models occurs at low temperature in static or pseudo-static conditions (T<=1 K). It arises from the influence of the dislocation segment in the 70°-mixed orientation with the (Ackland et al 2004 J. Phys.: Condens. Matter 16 S2629) potential and is seen in the critical line shape at which the dislocation breaks from the void. It affects τ_c for some combinations of void size and spacing. The effect on the line shape does not arise from anisotropy of the elastic line tension: it is due to the high Peierls stress of the 70° dislocation. When this effect does not control breakaway, the dependence of τ_c on void size and spacing follows an equation first found by modelling the Orowan process in the approximation of linear elasticity.