SUMMARY

Irradiation induces a high concentration of crystalline defects of various dimensionalities in the nuclear reactor cores, which are typically made of body centered cubic Iron (BCC Fe) and its alloys. The primary effect of irradiation is strain hardening which is thought to be caused by the blocking of dislocations by defects and defect clusters like point defects, self-interstitial loops, and voids. The dislocation-defect interactions are atomistic in nature due to the very small length and time scales involved (of the order of nanometers and picoseconds). To predict the effect of dislocation-defect interactions on the macroscopic mechanical and plastic behavior of the material necessitates robust coupling schemes by which atomistic details of the rate-limiting kinetic processes can be informed into coarser grained modeling schemes like crystal plasticity. Molecular dynamics (MD) simulations are conducted to study the physics of the processes controlling irradiation hardening and plastic behavior. Relevant atomistic processes are identified from the MD results and the unit process studies of the same are conducted using atomistic reaction pathway analyses like Nudged Elastic band method, as MD by itself is highly inefficient in capturing the rare events of the kinetic processes. Stress dependent activation energies and activation volumes are computed for the unit processes of thermally activated dislocation motion via kinkpair nucleation, dislocation pinning due to self interstitial atom etc. Constitutive laws are developed based on transition theory, that help inform the activation parameters into a coarse-grained crystal plasticity model. The macroscopic deformation behavior predicted by the crystal plasticity model is compared and validated with experimental results and the characteristic features explained in the light of atomistic knowledge of the constituting kinetics.