Investigation of the composite screw dislocation source activation in $\alpha$-iron with irradiation defects dispersion by dislocation dynamics

Overview & Synopsis

$\alpha$-iron steels are widely used as structural nuclear materials, thereby subjected to radiation-induced ageing mechanisms including hardening and embrittlement. These evolutions are usually ascribed to the formation of dispersed defect cluster populations, in the form of sessile dislocation loops. Beyond a critical dose, plastic straining becomes heterogeneous and can give rise to defect-depleted channels, where the defect-loops are progressively removed by interaction with the mobile dislocations. It is thought that channel-induced deformation can facilitate brittle fracture initiation, and is therefore regarded as a crucial damaging mechanism. In defect-depleted shear bands indeed, mobile dislocations emitted from random sources eventually intersect a defect cluster, arresting the incoming dislocation line . In this case, relatively long dislocation arms are present on both sides of the interacting defect. A screw-type arm can then change its glide plane through thermally activated cross-slip mechanism and resume gliding in its new crystallographic plane. This most typical and poorly understood configuration is here called a «composite» dislocation source, which will be examined by using DD simulations (Numodis).