Fabrication of bulk delta-phase Zirconium Hydride from Zircaloy-4 for use as moderators in microreactors

The fabrication of bulk delta-phase Zirconium Hydride ($\delta$-ZrH) using Zircaloy-4 as a precursor is herein reported. Characterization using electron-microscopy methods indicate that the fabricated material is of a single-phase. Sn-rich segregation zones have been observed to form as a direct result of the hydriding process. These findings experimentally validate previous \textit{ab initio} calculations on the influence H incorporation in Zircaloy-4 constitutional elements such as Sn, Fe and Cr. The effect of hydriding and Sn segregation on pre-existing Zr(Fe,Cr)$_{2}$ Laves phases is also evaluated. Major implications on the development of moderators for use in microreactors within the nuclear industry are discussed

Insights from Microstructure and Mechanical Property Comparisons of Three Pilgered Ferritic ODS Tubes

International audienceThree oxide dispersion strengthened alloys were fabricated into thin-walled (~500 µm wall thickness) tubes and characterized using x-ray, electron microscopy, and atom probe tomography methods. The three iron-based alloys included the 14%Cr alloy 14WYT, the 12%Cr alloy OFRAC, and a 10%Cr-6%Al alloy CrAZY. Each tube was subjected to a different thermal history during the pilgering process, which allowed for a detailed comparison between varying grain structures and alloy compositions. Atom probe tomography and energy-filtered transmission electron microscopy (TEM) comparisons showed good agreement in precipitate distributions, which matched predicted values using state-of-the-art nanoprecipitate coarsening models. The grain size, precipitate dispersion characteristics, and dislocation densities were then used to estimate yield strengths that were compared against room temperature axial and ring-pull tensile test data. For all three alloys, axial tensile specimens exhibited high tensile strength (>1 GPa) and reasonable plastic strains (10-17%). Ring tensile specimens, conversely, showed limited ductility (~1%) with similar strengths to those measured in the axial orientation. The strengthening models showed mixed agreement with experimentally measured values due to the highly anisotropic microstructures of all three ODS tubes. These results illustrate the need for future model optimization to accommodate non-isotropic microstructures associated with components processed using rolling/pilgering approaches

Coupled crystal orientation-size effects on the strength of nano crystals

We study the combined effects of grain size and texture on the strength of nanocrystalline copper (Cu) and nickel (Ni) using a crystal-plasticity based mechanics model. Within the model, slip occurs in discrete slip events exclusively by individual dislocations emitted statistically from the grain boundaries. We show that a Hall-Petch relationship emerges in both initially texture and non-textured materials and our values are in agreement with experimental measurements from numerous studies. We find that the Hall-Petch slope increases with texture strength, indicating that preferred orientations intensify the enhancements in strength that accompany grain size reductions. These findings reveal that texture is too influential to be neglected when analyzing and engineering grain size effects for increasing nanomaterial strength