In situ deformation of proton-irradiated molybdenum in a high-voltage electron microscope

Abstract Formation of defect-free zones (DFZs) (dislocation channelling) has been examined by in situ deformation in a high-voltage electron microscope. Interstitial-type dislocation loops have been introduced into molybdenum single crystals by proton irradiation using a compact cyclotron. The loops have a Burgers vector of b = (a/2) 〈111〉 lying on a {111} plane. It has been shown that these loops are absorbed or carried away by a group of moving dislocations, resulting in the formation of DFZs. Deformation in the zone is found to terminate by exhaustion of dislocation sources upon elimination of the loops and upon trapping of the glide dislocations at the zone matrix interface walls. Based on these observations the critical conditions required for formation of the DFZ are discussed with particular attention to the yielding asymmetry and the surface effect.