Application of dislocation dynamics to assess irradiation effect on materials with different grain sizes

Irradiation of materials by energetic particles produces defect clusters like vacancies, self-interstitial atoms and stacking-fault tetrahedra. These defect clusters form loops around existing dislocations, leading to their decoration and immobilization, which ultimately leads to radiation hardening in most of the materials. Effect of irradiation on material shear yield strength is analyzed using two-dimensional poly-crystal dislocation dynamics (DD) modelling. The plastic flow in the material is represented as collective behavior of a large number of edge dislocations distributed among many grains. The unit cell is assumed to have grains of hexagonal shape with uniform size. Grain boundaries are considered to be impenetrable to dislocations. The irradiation effects are modelled by taking all dislocations being locked by irradiation defects thus characterizing the fluence. When the total stress on the dislocations exceeds a critical stress value, they get unlocked and become free to move on their glide planes. Typical stress-strain curves for various critical values are obtained for irradiated Aluminium with different grain sizes, which reveal the effect of dislocation loops on increased yield stress as a function of both fluence and grain size. Critical locking stress is correlated to irradiation fluence by using single crystal yield stress values of irradiated Aluminium from DD analysis and corresponding experimentally available yield stress values.