Friction Stir Welding and Self-Ion Irradiation Effects on Microstructure and Mechanical Properties Changes with on Oxide Dispersion Strengthened Steel MA956

Joining processes for oxide dispersion strengthened (ODS) alloys remains a key challenge facing the nuclear community. The microstructure and mechanical properties were characterized in friction stir welded MA956 irradiated with 5 MeV Fe++ ions from 400 to 500°C up to 25 dpa. Nanoindentation was performed to assess changes in hardness and yield stress, and the dispersed barrier hardening (DBH) model was applied to described results. A combination of scanning transmission electron microscopy and atom probe tomography were used to assess evolution of the microstructure including dispersoids, dislocations and dislocation loops, nanoclusters, and solid solution concentrations. Overall, softening was observed as a result of increased dose and exacerbated at 500°C. The formation and coarsening of new dispersoids was noted while nanoclusters tended to dissolve in the base material, and were not identified in the stir zone. Solute nanocluster evolution was identified as a primary driver of the changes in mechanical properties.氧化物弥散强化（oxide dispersion strengthened, ODS）合金的连接工艺始终是核工业界面临的核心挑战。本研究针对经5兆电子伏二价铁离子辐照的搅拌摩擦焊态MA956合金展开系统性表征，辐照温度覆盖400℃至500℃，最高位移损伤剂量达25 dpa。通过纳米压痕（nanoindentation）测试评估合金硬度与屈服应力的变化，并采用弥散障碍强化（dispersed barrier hardening, DBH）模型对实验结果进行阐释。结合扫描透射电子显微镜（scanning transmission electron microscopy, STEM）与原子探针层析成像（atom probe tomography, APT）技术，表征了合金的微观组织演化过程，包括弥散相、位错与位错环、纳米团簇以及固溶体浓度的演变。整体而言，随着辐照剂量提升，合金出现软化现象，且在500℃时软化程度进一步加剧。研究观察到新弥散相的形成与粗化过程，而母材中的纳米团簇则趋于溶解，且搅拌区内未检测到纳米团簇。溶质纳米团簇的演化被确定为力学性能变化的主要驱动因素。