High-resolution STEM/EDS characterization of defect cluster complexes in reactor pressure vessel steel model alloys

Dislocation loop complexes with solute atoms were observed in this study using a high-resolution STEM/EDS analysis technique. In Fe-1.3Mn-0.6Ni alloy, Mn segregated along dislocation lines, and Ni segregated to the centers of dislocation loops. Mn, predominantly diffusing as mixed dumbbells with SIA, were driven to segregate toward tensile stress regions outside the dislocation edges, appearing near the dislocation lines. Conversely, when Ni diffused via the vacancy dragging mechanism, they were driven to segregate toward compressive stress regions inside the dislocation loop edges, manifesting as segregation at the centers of the loops. In contrast, in Fe-1.3Mn-0.6Ni-0.2Si alloy, Si addition inhibited this Ni segregation. This occurred because Si atoms preferentially interacted with point defects, thereby restricting the available diffusion pathways for Ni segregation. Furthermore, as Si is thermodynamically stable in solid solution, it did not undergo spontaneous segregation; instead, it indirectly inhibited Ni segregation by competing for point defect diffusion vehicles.