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.