Fine-scale microstructural characterization of pressure vessel steels and related materials using APFIM (atom probe field-ion microscope). [Atom probe field-ion microscopy]

Atom probe field-ion microscopy has been used to characterize the ultra fine-scale microstructure of neutron-irradiated A302B and A212B pressure vessel steels, A533B submerged arc welds, and several model Fe/endash/Cu Alloys. The atomic spatial resolution of this technique permits a complete microstructural and chemical description of the ultra-fine features that control the mechanical properties to be made. A variety of ultra fine-scale features including roughly spherical and disc-shaped copper precipitates and clusters, copper atmospheres, copper phosphides, phosphorus clusters, spherical and rod-shaped molybdenum carbides, molybdenum phosphides, disc-shaped molybdenum nitrides, and iron nitride precipitates were observed in these materials. The presence of these features was found to be material dependent. The atom probe also revealed a complex pattern of segregation and precipitation at grain boundaries and segregation to precipitate-ferrite interfaces. 22 figs.