Nanostructured Materials for Nuclear Applications II: Session II
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

Monday 2:00 PM
February 27, 2017
Room: Pacific 24
Location: Marriott Marquis Hotel

Session Chair: Fei Gao, University of Michigan; Osman Anderoglu, Los Alamos National Laboratory

2:00 PM  Invited
Radiation Interaction of Nanostructured Ceramics: Tiankai Yao1; Fengyuan Lu2; Jie Lian1; 1Rensselaer Polytechnic Institute; 2Louisiana State University
    The response of nanostructured materials upon intense displacive and ionizing radiations was systematically investigated to understand the synergistic effects of temperature and radiation on the behavior of nano-scale materials. The model systems include nanostructured zirconia, pyrochlore, ZrN, UO2 and ThO2, for both waste forms and fuel matrix applications. Nanostructured pyrochlores are not inherently radiation tolerant, and a correlation was identified among the phase stability, thermodynamics and defect behavior. Nanostructured ZrN are resistant to radiation damage-induced amorphization but experienced a structural contraction. UO2 and ThO2 with the grain size of a few nm in the powder form are stable against radiation-induced amorphization, but experience grain coarsening upon intense ion beam irradiation. Dense nano-sized UO2+X synthesized by spark plasma sintering shows stability against radiation–induced dissociation or grain coarsening upon heavy ion irradiations below 600 oC, consistent with the extreme stability of the high burn-up structure.

2:30 PM  Invited
Magnetic and Electrical Responses of Nanomaterials under Irradiation - New Type of Radiation Detection: You Qiang1; 1University of Idaho
    Nano-Nuclear Technology (NNT) deals with the use of engineered-nanomaterials for the improvement of performance and safety for the future generation nuclear reactors. Based on a review of NNT, this talk is focused on the fundamental understanding of fast responses in-situ and ex-situ on nanostructure evolution, magnetic and electrical property changing of nanomaterials under irradiations by use of He+, heavy (Si2+) ion beam and e-beam as well as heating. The contribution to the radiation sensitivity and stability were studied in details using Fe-based core-shell nanoparticle films. Investigation shows that the nanomaterials are good candidates for the radiation impact analysis and radiation environment applications. The results obtained from this investigation contribute to the scientific assessments done for predicting material performance in radiation environments and to recommend candidate nanomaterials for the development of high sensitive new type of radiation detectors and monitors in nuclear energy applications.

3:00 PM  
Point Defect Diffusion in Oxide Dispersion Strengthened Steels: Markus Mock1; Karsten Albe1; 1TU Darmstadt
    Nanoprecipitates in oxide dispersion strengthened (ODS) steels are crucial for the high temperature properties and are considered as sinks for point defects created during irradiation. The formation mechanism of nanoprecipitates and their influence on the irradiation tolerance is still a matter of debate. Yttrium is the slowest diffusing constituent of the precipitates which is known to be located on an off-lattice position bound to a neighboring vacancy. We present kinetic Monte Carlo calculations on the diffusion mechanism of yttrium in ODS steels based on diffusion barriers calculated with density functional theory (DFT) which reveal the migration mechanism of the yttrium-vacancy pair. Moreover we calculate the elastic dipole tensor for formation and migration of various point defects using DFT in order to asses the influence of strain on the sink strength of nanoprecipitates.

3:20 PM  
Defect Evolution in Stannate Pyrochlores under Swift Heavy Ion Irradiation: Chien-Hung Chen1; Cameron Tracy1; Maik Lang2; Christina Trautmann3; Rodney Ewing1; 1Stanford University; 2University of Tennessee; 3GSI Helmholtz Centre for Heavy Ion Research
    The ionic radius of A-site cations in stannate compounds with the pyrochlore structure (A2Sn2O7) strongly influences the energetics of order-to-disorder phase transformations under irradiation. In this work, the effects of dense electronic excitation by irradiation with 2.2 GeV Au ions on damage accumulation and ion-track morphology have been investigated using TEM. Based on the results of XRD and Raman spectroscopy, amorphization is more evident in compounds with larger ionic radius ratios, rA/rSn; whereas, disordering is favored in those with small rA/rSn. However, TEM observation of individual tracks indicates the presence of crystalline, disordered tracks in sample with a relative larger rA/rSn (i.e., Sm2Sn2O7), instead of the expected amorphous core surrounded by disordered or defect-rich track shell. This suggests a possible double impact mechanism for amorphization. This competition between amorphization and disordering will be discussed with attention to how results may differ depending on the length-scale of different analytical techniques.

3:40 PM Break

4:00 PM  Invited
Probing Nanoscale Damage Gradients in Irradiated Materials with Spherical Nanoindentation: Siddhartha Pathak1; Jordan Weaver2; Cheng Sun2; Yongqiang Wang2; Russ Doerner3; Surya Kalidindi4; Nathan Mara2; 1University of Nevada, Reno; 2Los Alamos National Laboratory; 3University of California at San Diego; 4Georgia Institute of Technology
    We discuss applications of spherical nanoindentation stress-strain curves in characterizing the local mechanical behavior of materials with modified surfaces. Using ion-irradiation as a specific example, we show that a simple variation of the indenter size (radius) can identify the depth of the radiation-induced-damage zone, as well as quantify the behavior of the damaged zone itself. Using corresponding local structure information from electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) we look at (a) the elastic response, elasto-plastic transition, and onset of plasticity in ion-irradiated tungsten, zirconium and 304 stainless steel under indentation, and compare their relative mechanical behavior to the unirradiated state, (b) correlating these changes to the different grain orientations as a function of (c) irradiation from different sources (such as He, W, and He+W for tungsten samples and proton irradiation in 304 stainless steel).

4:30 PM  
Radiation Effects on the Mechanical Properties of Nanoporous Gold: Nicolas Briot1; T. John Balk1; Remi Dingreville2; Khalid Hattar2; 1University of Kentucky; 2Sandia National Laboratories
     Because of the small volumes of materials that constitute the structure of nanoporous metals, their resistance to radiation damage has generated growing interest. Nanoporous gold (np-Au) is an excellent candidate for studying irradiation-induced damage, due to its tunable relative density and ligament size. The ligaments can have diameters as low as a few nanometers, in which defects created during irradiation can migrate to the free surfaces instead of accumulating in the material.The effects of ion irradiation on np-Au were investigated by microscopy and nanoindentation. Np-Au thin films were imaged in the TEM during irradiation, for samples with ligament size varying from a few nanometers up to ~75 nm. The inherent resistance to the accumulation of irradiation-induced defects will be discussed. In addition, bulk specimens were exposed to radiation and subsequently tested by nanoindentation. Results will be compared to other data obtained from bulk np-Au samples not exposed to radiation.

4:50 PM  
Radiation Resistance of a FeCr Model Alloy Nanostructured by Severe Plastic Deformation: Bertrand Radiguet1; Nariman Enikeev2; Marina Abramova2; Julia Ivanisenko3; Helena Zapolsky1; Xavier Sauvage1; Auriane Etienne1; Cristelle Pareige1; Ruslan Valiev2; 1GPM UMR CNRS 6634 - Université et INSA de Rouen; 2Ufa State Aviation Technical University; 3Institute of Nanotechnology, Karlsruke Institute for Technology
    The origin of the microstructural changes under irradiation is the super-saturation of point defects that can agglomerate in the form of loops or voids and can enhance or modify solute atom diffusion, resulting in enhanced or induced precipitation or segregation. In ultrafine grain (UFG) alloys, the volume fraction of grain boundaries is dramatically higher than in coarse grain (CG) materials. Since grain boundaries act as point defect sinks, a large part of irradiation induced defects can be annihilated. Therefore, a limitation of radiation damage is expected. The objective of the work presented here is to investigate the stability of nanostructured FeCr alloys under irradiation. A Fe-14%Cr model alloy was nanostructured by high pressure torsion in order to get grains of several tens of nanometers. Both CG anf UFG alloys were ion irradiated at 400°C. There microstructure was characterized by transmission electron microscopy and atom probe tomography.

5:10 PM  
Synthesis and Microstructural Characterization of Zirconium Oxide Dispersion Strengthened Model Alloy and 9 Cr Ferritic Steel: Raghavendra K G1; Arup Dasgupta1; Raj Narayan Hajra1; K. Jayasankar2; S. Saroja1; 1IGCAR Kalpakkam; 2CSIR-IMMT
    The ZrO2 dispersoid based ODS steel is reckoned as the Gen-2 ODS steel. In-depth understanding of the dispersoid requires study through concentrated model systems. Hence, this paper will focus on a Fe–15wt% ZrO2 model ODS alloy and a Fe-9Cr-2W-0.1C-0.35ZrO2 steel. Microstructural studies on the model ODS alloy showed that, crystallinity of ZrO2 was retained even after long durations of ball milling; circumstance under which, Y2O3 amorphizes. The milled powder also revealed fine nanocrystalline dispersoid and their homogeneous distribution. DSC, Synchrotron XRD and microscopic results suggested the formation of FeO phase and an transformation that was rather slow as long as the crystallites were nano. Further, the Fe-9Cr ODS steel powder synthesized under optimum conditions showed <5 nm sized dispersoids in nanocrystalline -Fe matrix. Powder consolidation is carried out by HIP. The formation of dispersoids, their chemistry and evolution during the material’s production will be discussed in detail.