Interactions between an edge dislocation and Frank loops in Ni3Mo and pure Ni: atomistic mechanisms and a mechanism-based hardening model

摘要: Irradiation-induced dislocation loops impede dislocation motion and degrade Ni-based structural materials in molten salt reactors. However, the dislocationloop interaction mechanisms, predictive models for loop hardening, and the role of alloying elements remain unclear. Using atomistic simulations, we investigate interactions between gliding edge dislocations (be = 1/2[110]) and Frank loops (bL = 1/3<111>) in Ni3Mo as a model material and pure Ni as a reference. The effects of bL orientation, temperature and strain rate are systematically analyzed. Results show two primary interaction mechanisms: loop absorption and loop shearing. These mechanisms depend on the relative orientation of bL to be, but are insensitive to temperature and strain rate. Loop absorption involves screw dislocation dipole formation near the loop and subsequent dislocation unpinning by cross-slip of this screw dipole, requiring a higher stress than shearing the loop. In Ni3Mo, the strength of loop absorption decreases with increasing temperature but remains almost unchanged with strain rate, because the dislocation unpinning stress decreases faster than the lattice resistance as the strain rate decreases. The strength of loop shearing is hardly affected by temperature and strain rate, but is slightly influenced by Mo addition. A mechanism-based hardening model incorporating both solute atom and irradiation loop effects is developed. It treats loop absorption as a thermally activated process of edge dislocation overcoming barriers and describes the temperature dependence of dislocation unpinning stress using a parabolic function. The model predicts loop hardening at experimental strain rates, agreeing with experimental results for several Ni-based alloys.