Unveiling the dislocation mechanism induced by irradiation defects in austenitic FeCrNi alloy

Understanding the interaction between irradiation defects and gliding dislocations is crucial for achieving strength-ductility synergy in irradiated nuclear structural materials for reactor safety and longevity. Here, we employ MD to investigate irradiation-induced defect formation and their interactions with gliding dislocations in a polycrystalline FeCrNi alloy during tensile deformation. Our findings reveal that stacking faults (SFs) were nucleated from the local stress concentration region on grain boundaries caused by absorbing point defects, and gradually transformed into twin with increasing irradiation dose. The density of sessile stair-rod loops, in contrast to the dynamic equilibrium observed for mobile Shockley loops, exhibits an increasing trend with higher irradiation doses and tends to aggregate into stacking fault tetrahedra (SFT) at the later stages of irradiation. During plastic deformation, in addition to the hindering effect inducing radiation hardening, it was also found that Shockley loop could facilitate double cross-slip of screw dislocations at adjacent crystal planes, which complicates dislocation motion and sustains ductility. Additionally, irradiation-induced voids can trigger dislocation renucleation through interacting with a pair of dislocations with opposite signs, leading to the transformation of SF into nanotwin, thus mitigating ductility loss. These mechanisms driven by 3D grain boundary network and random defect distributions offer novel insights into designing radiation-tolerant polycrystalline FeCrNi alloys for nuclear applications.