Image force on a dislocation in a bcc bicrystal: Computer investigation of core effects

The 'image force' on a dislocation situated a few interatomic distances from the interface separating two welded half-crystals is investigated by computer simulation. The two half-crystals have bcc structure, with the same lattice parameter and orientation, but have different elastic moduli. The dislocation has the 1/2〈111〉 Burgers vector and a screw character; the interface is along a {112}- or {110}-type plane, parallel to the dislocation. Using a Finnis-Sinclair type of potential for α-Fe, the total strain energy stored in the bicrystal is calculated as a function of the dislocation position, giving the image force by derivation. The modifications in lattice friction (Peierls stress) and the changes in the dislocation core are investigated in the neighbourhood of the interface. Results are compared with those previously obtained for the planar core 〈100〉 screw dislocation. All these simulation results are finally compared with the predictions of the Peierls-Nabarro-based model of Pacheco and Mura. Despite some limitations, it is shown that this model can be extended for deriving a general law for the image force in the interface region, provided that some measure of the core width is explicitly introduced.