Microstructural Processes in Irradiated Materials: Zr-Alloys and Advanced Modeling
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Thak Sang Byun, Pacific Northwest National Laboratory; Chu-Chun Fu, Commissariat Ó l'Únergie atomique et aux Únergies alternatives (CEA); Djamel Kaoumi, University of South Carolina; Dane Morgan, University of Wisconsin-Madison; Mahmood Mamivand, University of Wisconsin-Madison; Yasuyoshi Nagai, Tohoku University

Thursday 8:30 AM
March 2, 2017
Room: Del Mar
Location: Marriott Marquis Hotel

Session Chair: Enrique Martinez Saez, Los Alamos National Laboratory; Fabien Onimus, CEA-Saclay

8:30 AM  Invited
Deformation Mechanisms and Radiation Induced Damage in Zirconium Alloys: A Multi-scale Approach: Fabien Onimus1; L. Dupuy1; Frederic Mompiou2; M. Bono1; 1CEA; 2CEMES-CNRS
    Zirconium alloys are used as cladding tubes for the fuel of nuclear water reactors. In-reactor, zirconium alloys are subjected simultaneously to mechanical loadings and neutron irradiation. In order to gain a better understanding of the radiation effect on deformation mechanisms and on the resulting mechanical behavior, a multiscale study has been undertaken. Mechanical tests have been conducted on neutron irradiated tubes. The deformation mechanisms have been analyzed by TEM. A process of removal of irradiation defects by gliding dislocations has been observed. Then Zr ion irradiations have been performed allowing conducting tensile tests in situ, inside the TEM. Interactions between dislocations and irradiation defects have been observed in situ and also simulated using a novel dislocation dynamics code. Finally, a polycrystalline model, that takes into account these mechanisms, has been developed and compared, with success, to both loading path change tests and TEM observations.

9:00 AM  
Quantifying Irradiation-induced Defect Densities in Zr Through Changes in X-ray Diffraction Line Profiles - Insights from Atomistic Modeling.: Rory Hulse1; Christopher Race1; Michael Preuss1; 1University of Manchester
    Irradiation-induced growth (IIG) of Zr-alloy nuclear fuel cladding under irradiation can limit the service life of nuclear fuel. IIG is believed to occur due to the formation and growth of dislocation loops. Current efforts to create Zr-alloys that are resistant to IIG rely on accurate determination of dislocation density and type in irradiated candidate alloys. X-ray diffraction (XRD) can, in principle, provide this information via an analysis of changes to the diffraction peak shapes. However uncertainty exists in correlating XRD data to defect density and type for the case of irradiation-induced defects. We have utilized atomistic models of controlled defect populations in pure Zr to generate theoretical XRD profiles. These are compared with experimental profiles and changes in line shape are analyzed in terms of contributions from the strain fields of individual defects. These insights will allow more accurate quantification of irradiation-induced defects with XRD.

9:20 AM  Cancelled
Effects of Heavy-ion (Zr+) Irradiation on Zr-2.5Nb Alloy Studied by X-ray Diffraction, Nanoindentation, and TEM: Qiang Wang1; Levente Balogh1; Mark Daymond1; Zhongwen Yao1; 1Queen's University
    Zr-2.5Nb pressure tube alloy was irradiated by Zr+ along both transverse and axial directions of the tube at room temperature. X-ray diffraction and nanoindentation test have been carried out to investigate the developments of irradiation defects and hardness. The X-ray diffraction was conducted at room temperature while the hardness was test from room temperature to 350░C. The dislocation densities, arrangements, and characters were quantitatively determined by modern whole pattern diffraction line profile analysis (DLPA). Both X-ray diffraction and hardness results showed obvious orientation dependence. Hardness of the cross-sectional samples was also tested. Post-mortem studies of the irradiated and deformed samples were conducted by Transmission Electron Microscope (TEM). The results were discussed in terms of irradiation effects, microstructural distributions and plastic deformation mechanisms.

9:40 AM  
In-Situ TEM Triple Beam Irradiation of Zirconium Alloys at Elevated Temperature: Brittany Muntifering1; Khalid Hattar1; David Senor2; Clark Snow1; 1Sandia National Laboratories; 2Pacific Northwest National Laboratory
    The aggressive environment of nuclear reactors present a wide range of material challenges. This is exemplified in the tritium-producing burnable absorber rod (TPBAR), in which displacement damage, helium production, and hydrogen isotope production all occur simultaneously at elevated temperatures. In this in-situ ion irradiation transmission electron microscope (TEM) experiment, we examined the effects of zirconium alloys to both sequential and concurrent implantations of 10 keV D2 and He ions, as well as 3 MeV zirconium ions, all done at 300 ˚C. Defect evolution, including dislocation loop and cavity growth, was characterized as a function of irradiation order and synergy. The culminating study of this investigation was an overnight in-situ triple beam irradiation experiment at elevated temperatures. Finally, detailed post-irradiation examination was done to understand the long term stability of zirconium alloys exposed to these combinations of aggressive and complex environments.

10:00 AM Break

10:15 AM  Invited
Thermal Activation of Dislocations in Large Scale Obstacle Bypass: Enrique Martinez Saez1; Cameron Sobie2; David MacDowell2; Laurent Capolungo1; 1Los Alamos National Laboratory; 2Georgia Institute of Technology
    Dislocation dynamics simulations have been used extensively to predict hardening caused by dislocation-obstacle interactions. Transition state theory (TST) enables direct access to thermally activated reaction rates of dislocation-obstacle bypass processes. Moving beyond unit dislocation-defect reactions to a representative environment containing a large number of defects requires coarse-graining the activation energy barriers of a population of obstacles into an effective energy barrier that accurately represents the large scale collective process. The work presented here investigates the relationship between unit dislocation-defect bypass processes and the distribution of activation energy barriers for an obstacle ensemble. The significant difference observed is attributed to the inherent cooperative nature of dislocation bypass processes. A phenomenological model for activation energy stress dependence is shown to describe well the effect of a distribution of activation energies, and a probabilistic activation energy model incorporating the stress distribution in a material is presented.

10:45 AM  
Dynamics of Interaction between Point Defects and Dislocations in bcc Iron Using SEAKMC Simulations: Haixuan Xu1; 1University of Tennessee
    The interaction between radiation induced defects with dislocations plays a central role in the subsequent microstructural evolution and property changes, e.g. the void swelling caused by dislocation bias. In this work we investigate the dynamics of the interaction of vacancies and interstitials with perfect isolated edge and screw dislocations in bcc iron. The saddle point distribution of a point defect near a dislocation is sampled using self-evolving atomistic kinetic Monte Carlo (SEAKMC). The anisotropic effects caused by the dislocation on migration energy barriers are examined. The results show that the dynamics of interaction between point defects and dislocations controls the interaction probability and the interaction radius is different from the estimation based on the binding energies. This study also provides insights on how to tune the interaction to better partition radiation induced defects and increase radiation resistance.

11:05 AM  
Multi-scale Modeling of Vacancy-mediated Solute Diffusion Near an Edge Dislocation under Irradiation: Zebo Li1; Trinkle Dallas2; Thomas Garnier2; Venkateswara Manga3; Maylise Nastar4; Pascal Bellon2; Robert Averback2; 1Department of Nuclear, Plasma, Radiological Engineering, University of Illinois, Urbana-Champaign; 2Department of Materials Science and Engineering, University of Illinois, Urbana-Champaign; 3Materials Science and Engineering, University of Arizona; 4CEA, DEN, Service de Recherches de Metallurgie Physique
    Simulating dislocation climb and solute segregation under irradiation requires a quantitative description of diffusion of vacancies and solutes to dislocations. We develop a coupled multi-scale simulation for diffusion of vacancies and solutes in an FCC metal near an edge dislocation under irradiation. A near-lattice model is used for the dislocation core to capture the atomic transitions. Simultaneously, we use a continuum phase field method to model the domain outside the core, with concurrent coupling in an overlapping region. The heterogeneous, anisotropic stress field around the dislocation affects the vacancy distribution and the flow pattern of vacancies and solutes. We apply our model to Ni-Si, where the increased vacancy concentration due to irradiation drives dislocation climb and segregation of Si atoms near the dislocation core. We predict precipitation near the core for undersaturated alloys under irradiation, and changes in climb rates due to Si.

11:25 AM  
Multiscale Simulation of Fast Neutron Damage in Beryllium: Pavel Vladimirov1; Vladimir Borodin2; 1Karlsruhe Institute of Technology; 2National Research Center “Kurchatov Institute”
    Production of atomic displacement cascades by fast neutrons inherently involves several spatial and time scales implying application of the appropriate simulation methods. Binary collision (BC), molecular dynamics (MD) and ab initio approaches were successfully used to develop suitable multiscale approach for studying displacement damage in beryllium. Primary knocked-on atom (PKAs) spectra are calculated using neutron spectra of fusion and typical materials testing (MTR) reactors. Then BC code is used for obtaining PKA distribution with energies below subcascade formation threshold. Collected library of low-energy displacement cascades calculated by MD is employed to deduce the total number of defect clusters integrating over the obtained PKA distribution and adding Frenkel pairs created by the high-energy PKAs. The threshold displacement energy calculated by ab initio was applied for appropriate correction of MD results. This approach allows comparing effect of fusion and common MTR neutrons and obtaining better insights on microstructural changes under neutron irradiation.

11:45 AM  
Multiscale Modelling of Patterned Microstructures in Irradiated Mmaterials: Application to AgCu Alloy: Gilles Demange1; David Simeone2; Laurence Luneville3; Vassilis Pontikis4; 1GPM/ERAFEN, UniversitÚ de Rouen; 2DEN/DMN/SRMA/LA2M, CEA Saclay; 3DEN/SERMA/LLPR, CEA Saclay; 4DEN/DMN/LSI, CEA Saclay
    Manufactured microstructures have become of crucial technological interest, as they could provide materials with desired physical properties. Recently unusual steady state patterned microstructures in irradiated materials have been observed. These microstructures result from a ballistic disordering induced by the slowing down of impinging particles such as ions. In this work, a multiscale approach based on molecular dynamics, Monte-Carlo and phase field has been applied to simulate the microstructure’s evolution in AgCu alloy under Krypton ions irradiation. To study the influence of irradiation on diffusion kinetics the ballistic term was implemented in phase field model. The influence of irradiation flux and temperature on the main characteristic of pattering structure has been investigated. Finally, the phase diagram of the irradiated system provided by our numerical phase field approach is presented.