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

Abstract

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