Exploring Complex Patterns: How Cold Work Modulates Defect Evolution and Radiation Resistance in CLF-1 Steels Under Multi-Beam Ion Irradiations

China Low-Activation Ferrite (CLF-1) steel, renowned for its excellent thermomechanical properties and irradiation resistance, plays a key role in the development of the R&D of the Chinese Helium-Cooled Ceramic Breeding Test Blanket Module. Cold-worked CLF-1 steels were irradiated with sequential dual ion beams of (Fe2+ and H+), followed by single He+ irradiation at 723 K, with a dose rate of 1.09 dpa/h, to explore the complex relationship between cold work, defect evolution, and irradiation hardening. Samples with cold-working deformations of 0%, 10%, and 50% (denoted as CW 0%, CW 10%, and CW 50%, respectively) were examined. The results based on nanoindentation, TEM, and EBSD reveal that moderate cold work (10%) introduces dense dislocations, acting as effective sinks to suppress irradiation-induced defect accumulation and hardening, while excessive cold work (50%) triggers partial recrystallization under relatively long-time multi-beam irradiation, reducing dislocation density, which leads to the comparable hardening with CW 10%. In contrast, non-deformed samples (0% cold work) exhibit severe irradiation hardening (38.46%). He bubbles and dislocation loops follow non-monotonic trends in number density (CW 50% < CW 0% < CW 10%) and size (CW 50% > CW 0% > CW 10%), governed by the interplay of sink efficiency, thermal diffusion, and recrystallization. These findings highlight that a moderate level of cold-working deformation contributes to enhancing the sink strength, thereby offering a viable approach for designing radiation-tolerant RAFM steels.