Nanostructured Materials for Nuclear Applications II: Session III
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Nanomechanical Materials Behavior Committee, TMS: Nuclear Materials Committee
Program Organizers: Cheng Sun, Idaho National Laboratory; Khalid Hattar, Sandia National Laboratories ; Celine Hin , Virginia Tech; Fei Gao , University of Michigan; Osman Anderoglu , Los Alamos National Laboratory; Mitra Taheri , Drexel University; Haiming Wen , Idaho State University

Tuesday 8:30 AM
February 28, 2017
Room: Pacific 24
Location: Marriott Marquis Hotel

Session Chair: Fei Gao, University of Michigan; Eda Aydogan, Los Alamos National Laboratory

8:30 AM  Invited
Nano-particles Control for High Performance ODS Steels: Akihiko Kimura1; 1Kyoto University
    The characteristic radiation effects, which are no-loss-of-elongation, excellent swelling resistance and suppression of He-induced grain boundary embrittlement, of oxide dispersion strengthened steels are introduced, and the effects of interfaces, such as nano-scaled oxide particles/matrix and grain boundaries, on the radiation tolerance are discussed from the view of effects of trapping and absorbing point defects and their clusters. The high performance of the ODS steels demands dense dispersion of nano-scaled oxide particles, which is significantly affected by the small addition of oxide former elements like Ti, Zr and Hf. The fine oxide particles in the Zr-added FeCrAl-ODS steels can be identified to be yttria-zirconia that has three structures, defected fluorite, pyrochlore and delta-phase. It is shown that the structure of the yttria-zirconia depends on zirconium composition. The mechanism refining oxide particles is also discussed based on the detailed microstructure examinations by HR-TEM and STEM/HAADF.

9:00 AM  
Varying Responses of Nanocrystalline Structures to Assorted Irradiation Conditions: Brittany Muntifering1; Daniel Bufford1; Khalid Hattar1; 1Sandia National Laboratories
    There currently exists inconclusive and often times contradictory information regarding the radiation stability of nanostructured materials. This talk will highlight some recent in-situ ion irradiation transmission electron microscopy experiments in nanocrystalline metals performed at Sandia National Laboratories including gold, palladium, copper, zirconium, nickel and iron. The stability was explored in ion radiation environments ranging from deuterium to gold, with energies as low as 10 keV reaching 48 MeV, at temperatures up to 800 ˚C. In addition, damage ranging from single ion strikes up to tens of DPA have been investigated. The work will be compared to simulations investigating grain boundary mobility and sink theory. This work was partially supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

9:20 AM  
Microstructural Characterization of ATR Irradiated Cu/Nb Nanolayered Composites: Osman Anderoglu1; Peter Hosemann2; Amit Misra3; George Odette4; Michael Nastasi5; Stuart Maloy1; 1Los Alamos National Laboratory; 2University of California-Berkeley; 3University of Michigan; 4University of California-Santa Barbara; 5University of Nebraska
    Nanolayered materials show improved resistance to irradiation compared to bulk counterparts due to presence of a high volume ratio of interfaces that provide recombination sites for point defects. In addition, the interfaces can also trap He in the form of small bubbles/clusters retarding the formation of cavities. However, almost all of the work was carried out using accelerator based techniques. To assess the performance of these alloys in a reactor for the first time, nanolayered free standing Cu/Nb films with 5, 20 and 40 nm layer thickness were irradiated in ATR. The irradiation temperature ranges 275-750C with a total dose of ~6 dpa. Furthermore, the Cu/Nb films were also Ni coated to implant He during irradiation. In this talk, the results of neutron irradiations on microstructure from selected dose and temperatures will be discussed.

9:40 AM  
Kinetics of Initial Phase Separation and Coarsening of Nanoscale Phase in Fe–Cr Alloys: Zhilong Yan1; Yongsheng Li1; Xiaorong Zhou1; 1Nanjing University of Science and Technology
    High-Cr ferrite-martensite stainless steels are used in the cooling pipes of nuclear power plants because of their excellent anti-radiation performance and mechanical properties at high temperatures. While the separation of Cr-enriched α' phases induces the embrittlement of Fe-Cr alloy. Dynamics of Cr-enriched α' phase from initial phase separation to coarsening in the Fe–Cr alloys are studied by the three-dimensional phase-field simulation. The separation of α' phase by nucleation and growth goes through the stages of nucleation, nucleation and growth, growth and coarsening and steady state coarsening. As the aging temperature decreases, the coarsening time exponent n of the average radius increases and the coarsening rate constant k decreases. As the composition increases, the coarsening time exponent n and the coarsening rate constant k increase at the steady state coarsening stage. The maximum of number density increases as temperature decreases and composition increases.

10:00 AM Break

10:20 AM  Invited
Using Atom Probe Tomography and Neutron Inventory Simulation to Investigate Neutron-Irradiation-Induced Nano-Scale Second Phase Precipitation Chemistry in Pure Tungsten Irradiated at HFIR: Philip Edmondson1; Mark Gilbert2; 1Oak Ridge National Laboratory; 2EURATOM/CCFE Fusion Association
    Tungsten has been proposed as a plasma-facing material for future nuclear fusion reactors, in part due to its ability to withstand the harsh operational environment: high temperatures, intense neutron flux, radiation damage, etc. However, under neutron-irradiation the constituent tungsten atoms may undergo transmutation to other species including – predominantly – rhenium and osmium, which may then accumulate and produce second-phase precipitates that embrittle the material. In this work, the time-of-flight spectrometer functionality of today’s modern atom probe microscope has been used in conjunction with detailed inventory calculations to examine the formation and chemistry of the second-phase precipitates in a pure tungsten specimen neutron-irradiated in the HFIR reactor up to doses of ~2 displacements-per-atom at 750C. The morphology and chemistry of these precipitates will be discussed focusing on the interface between precipitate and matrix, and how the combined use of these techniques can provide more detailed insights in high-transmutation-product-bearing nuclear materials.

10:50 AM  
Design of Radiation-resistant Alloys: Thomas Schuler1; Dallas Trinkle1; Pascal Bellon1; Robert Averback1; 1University of Illinois at Urbana-Champaign
    The design of nanoscale microstructures is a promising way to develop radiation-resistant alloys. Since these micros tructures are obtained under out-of-equilibrium processing routes they may be unstable under irradiation. An alternati ve to nanopatterning is to introduce specific solutes which show attractive binding with point defects. These solutes would act as recombination centers, reducing the driving force for void and self-interstitial loop formation. Setting the solute concentrations below solubility limits ensures the stability of the solid solution in most cases. We present a multi-scale study of FCC alloys (Cu and Al) in which some solutes are added to trap point defects. Ener gy parameters are computed ab initio, and then used as inputs in a self-consistent mean-field approach to obtain trans port coefficients. Finally, we perform phase field simulations of microstructure evolution under irradiation using thi s atomic-scale information. The results are compared with experimental observations on irradiated materials.

11:10 AM  
Exploring the In-plane Distribution of Helium Bubbles at Cu/V Interfaces: Di Chen1; Nan Li1; Kevin Baldwin1; Dina Yuryev2; Michael Demkowicz3; Yongqiang Wang1; 1Los Alamos National Laboratory; 2Massachusetts Institute of Technology; 3Texas A&M University
    Helium (He) precipitates aggregate at defects, such as dislocations, grain boundaries and interfaces. In this talk, we explore the planar distribution of He bubbles at Cu/V interfaces using transmission electron microscopy (TEM). In Cu/V bilayers, bubbles form along extrinsic dislocation segments deposited on the interface by threading dislocations. In V/Cu/V trilayers, interfacial He bubble aggregation depends on the crystallographic character of the interfaces present in the composite. Our findings suggest methods of manipulating the distribution of He bubbles through tailoring of interface dislocation structure.

11:30 AM  
Atom Probe Tomography Study of Neutron Irradiated U-Mo Fuel: Haiming Wen1; Assel Aitkaliyeva2; Yaqiao Wu3; Bandon Miller2; Dennis Keiser2; Jian Gan2; 1Idaho State University; 2Idaho National Laboratory; 3Boise State University
    U-Mo fuel has been developed for application in high performance research reactors. Previous transmission electron microscopy investigations of neutron irradiated U-Mo fuel have revealed a fission gas bubble superlattice. However, the chemical compositions of the fission gas bubbles and the matrix have not been measured, and the possible relations between the fission gas bubbles and solid fission products remain unclear. Atom probe tomography (APT) is a powerful tool to advance the understanding of microstructure of nuclear fuels and materials at the atomic level. This study is the first APT investigation of neutron irradiated U-Mo fuel. Various fission products were identified in the APT samples. Fission gas bubble superlattice was seen in some orientations. The chemical composition, number density and volume fraction of fission gas bubbles and the chemical composition of the matrix were measured. The distribution of solid fission products and their relations to fission gas bubbles were also obtained.