Structural changes at grain boundaries in bcc iron induced by atomic collisions

Symmetrical tilt and twist grain boundary structures have been simulated in bcc iron using a many-body potential of the Finnis-Sinclair form. Initial structures were relaxed to the local minimum energy configuration using molecular dynamics. The width and relative energies of the resulting grain boundaries have been calculated. Collision cascades have been initiated in the structure by imparting initial energy to a single Fe atom and the interaction of the cascade with the grain boundary has been studied again using molecular dynamics simulations. The cascades were chosen where the primary knock-on atom (PKA) had initial energy of 1 keV and the orientation and distance of the PKA were changed in order to generate some statistical information concerning the radiation damage near the interface. The results show an increased radiation damage in the grain boundary region compared to the bulk material. The interstitials that form in the boundary region seem to be stable and do not move away from the boundary during the recrystallisation phase of the collision cascade. Clusters of interstitials are easily produced at the boundary in either structure but the defects induced near the twist boundary are more extensive that those near the tilt boundary. PACS numbers: 71.15.Pd, 61.80.-x, 61.72.Mn