Abstract
Joining nanostructured ferritic alloys (NFAs) has proved challenging, as the nano-oxides that provide superior strength, creep resistance, and radiation tolerance at high temperatures tend to agglomerate, redistribute, and coarsen during conventional fusion welding. In this study, capacitive discharge resistance welding (CDRW)—a solid-state variant of resistance welding—was used to join end caps and thin-walled cladding tubes of the NFA 14YWT. The resulting solid-state joints were found to be hermetically sealed and were characterized across the weld region using electron microscopy (macroscopic, microscopic, and nanometer scales) and nanoindentation. Microstructural evolution near the weld line was limited to narrow (~50–200 μm) thermo-mechanically affected zones (TMAZs) and to a reduction in pre-existing component textures. Dispersoid populations (i.e., nano-oxides and larger oxide particles) appeared unchanged by all but the highest energy and power CDRW condition, with this extreme producing only minor nano-oxide coarsening (~2 nm → ~5 nm Ø). Despite a minimal microstructural change, the TMAZs were found to be ~10% softer than the surrounding base material. These findings are considered in terms of past solid-state welding (SSW) efforts—cladding applications and NFA-like materials in particular—and in terms of strengthening mechanisms in NFAs and the potential impacts of localized temperature–strain conditions during SSW.
Highlights
Clean and affordable next-generation nuclear power systems are essential ingredients to achieve energy security and meet targets for greenhouse gas reduction
We explored the use of capacitive discharge resistance welding (CDRW) to join cladding tubes and end caps made from the nanostructured ferritic alloys (NFAs) 14YWT
These thermo-mechanically affected zones (TMAZs) are differentiated from the unaffected materials of the cap and tube by the warping of pre-existing textures, with grains appearing to bend to lie parallel to the weld line, as shown in Figure 2b, and are thinner in the caps than in the tubes
Summary
Clean and affordable next-generation nuclear power systems are essential ingredients to achieve energy security and meet targets for greenhouse gas reduction. Y2 TiO5 particles that are formed using high-energy mechanical alloying, consolidation, and heat treatment of steel powders with small quantities of titanium and yttria (Y2 O3 ) These dispersoids allow for NFAs to improve on the performance of other ODS materials by pinning grain boundaries and dislocations—for superior grain size stability and creep resistance at high temperature [9,14,15]—and by providing recombination and trapping sites for radiation-induced point defects and helium—for reduced swelling, embrittlement, and chemical segregation with irradiation [16,17,18,19,20,21]
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