2, Argonne National Laboratory, Chicago, Illinois, United States
High-temperature ultrafine precipitation strengthened steel (HT-UPS) is a candidate structural material for advanced nuclear reactors because of its high temperature creep resistance. However, little is currently known about its structure following irradiation. Neutron irradiation induces defect structures over multiple length and time scales. This research examines the three-dimensional (3D) microstructural response of HT-UPS to low neutron doses (0.01, 0.1, and 1 dpa) at ~600oC. This work will focus on the mesoscale evolution of HT-UPS using high-energy X-rays. High-energy X-rays can provide 3D, non-destructive characterization to study both microstructural and micromechanical aspects. Both far field high-energy diffraction microscopy (FF-HEDM) and near field (NF)-HEDM techniques were used to characterize polycrystalline HT-UPS samples at the Advanced Photon Source. FF-HEDM provides information about center-of-mass, orientation, and strain states of individual grains. NF-HEDM provides inter and intra-granular crystallographic orientation information, akin to non-destructive electron backscatter diffraction, but in 3D. In the present work, FF- and NF-HEDM will be used to quantitatively study these features in irradiated HT-UPS specimens. These results will be compared to the identical, previously unirradiated HT-UPS specimens. This will be first of its kind 3D microstructural comparison study between neutron irradiated and unirradiated materials.