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

Monday 8:30 AM
February 27, 2017
Room: Del Mar
Location: Marriott Marquis Hotel

Session Chair: Philip Edmondson, Oak Ridge National Laboratory; Philippe Pareige, Rouen University

8:30 AM Introductory Comments

8:35 AM  Invited
Atom Probe Characterization of Microstructures in Irradiated Materials: Philippe Pareige1; Bertrand Radiguet1; Auriane Etienne1; Cristelle Pareige1; 1Rouen University
    Atom Probe Tomography (APT) allows to explore matter at the atomic scale to understand microstructural evolution of nuclear reactor pressure vessel steels or internals under neutrons (or other particles) irradiation. Specific sample preparations and correlative microscopies (APT and TEM)give new possibilities and bring additional informations to understand irradiation effects but also to support modeling. This state of art combination of techniques is available at the GPM laboratory in the GENESIS platform. However, APT data mining requires careful attention to give a correct description of the material at this ultimate atomic scale.In this presentation recent results and benchmarking on irradiated materials will be presented.

9:05 AM  
On the Influence of the Irradiation Depth on the Microstructural Evolution of FeCrX (X=Ni,Si,P) Alloys under Ion Irradiation: Begońa Gómez-Ferrer1; Cristelle Pareige1; Philippe Pareige1; 1University of Rouen
     The in-service behavior of high-Cr Ferritic-Martensitic steels –candidate structural alloys in future GEN IV and fusion reactors—is a key issue that requires a deep understanding of the microstructural changes operating under neutron-irradiation. Nevertheless, given the complexity of these processes and the restricted access to neutron-irradiations, the community focuses on model experiments performed on Fe-Cr alloys using ion-irradiations as alternative. However, transferability issues arise. In neutron irradiated Fe-Cr alloys (>9%) at 300°C α/α' decomposition was observed at low dose but not under ion-irradiation. Also, in low purity Fe-Cr model alloys, formation of NiSiPCr-enriched clusters formed under both ion and neutron irradiations was revealed with Atom Probe Tomography (APT). Within the framework of the European FP7/MatISSE project, FeCrX (X=Ni,Si,P) model alloys have been self-ion irradiated at 5 MeV and 300°C at two different fluences. APT characterization along the implantation profile provides insights on the origin of the differences and commonalities described.

9:25 AM  
Prismatic Dislocation Loop Interaction with Free Surface in BCC Metals: Jan Fikar1; Roman Gröger1; Robin Schäublin2; 1IPM; 2ETHZ
    The prismatic loops appear in metals as a result of high-energy irradiation. Understanding their formation and interaction is important for quantification of irradiation-induced deterioration of mechanical properties. Characterization of dislocation loops in thin foils is commonly done using transmission electron microscopy (TEM), but the results are inevitably influenced by the proximity of free surfaces. The prismatic loops are attracted to free surfaces by image forces. Depending on the type, size and depth of the loop in the foil, they can escape to the free surface, thus invalidating TEM observations and conclusions. We present an easy applicable and general method to estimate the critical depth for various dislocation loops in the thin foil and to correct the TEM measurements. The method is verified by atomistic simulations in BCC iron and tungsten on dislocation loops with Burgers vector 1/2<111> and <100> and with various shapes.

9:45 AM  
Determination of the Type, Burgers Vector and Density of Dislocation Loops by X-ray Line Profile Analysis in Proton Irradiated Zr Alloys: Tamás Ungár1; Matthew Topping1; Philipp Frankel1; Michael Preuss1; 1The University of Manchester
    Within extreme environment of fast neutron irradiation, high temperature and corrosive cooling media Zr claddings exhibit dimensional instabilities as a result of irradiation induced growth, creep and hydrogen pick up. With volume conserving conditions, irradiation damage produces axial expansion and radial contraction due to formation of dislocation loops in Zr fuel cladding with strong split basal texture. Two main dislocation types form, a-loops with {10-10} and c-loops with (0002) habit planes. Since neutron irradiated Zr is not readily available, particular at low fluence levels, proton irradiation is increasingly used as a surrogate. In this lecture we show that advanced synchrotron and laboratory X-ray line profile analysis is a powerful tool, complementary to electron microscopy, to characterize the dislocation structure in proton irradiated Zr and its alloys. Diffraction patterns are evaluated in terms of Burgers vector population and partial dislocation loop densities of a- and c-type loops by the CMWP procedure.

10:05 AM Break

10:20 AM  
High Resolution EBSD and Strain Mapping of Nanoindentatation in Ion-irradiated Steels: Anna Kareer1; Hamid Abdolvand2; Steve Roberts1; 1University of Oxford; 2Western University
    Ferritic/martensitic steels are leading candidate materials for structural components in future Gen IV reactors. Determining mechanical properties of these materials after exposure to irradiation is essential for the safe design of the reactor. Self-ion irradiation can be used to emulate the damage produced from neutron irradiation. Damage is limited to small volumes of material, thus testing techniques of a similar length scale are required such as nanoindentation. However, obtaining unambiguous mechanical property data is currently difficult due to experimental artefacts including surface contamination, size effects and a dose profile varying with depth. In this study, high resolution EBSD followed by a strain mapping analysis was used to quantify the plastic zone beneath the indent. The plastic zone size is shown to be affected by exposure to irradiation. This is used to inform the analysis of hardness – depth nanoindentation data, allowing better extraction of macroscopic flow properties from these tests.

10:40 AM  Invited
Deformation Behavior of Ion-irradiated Materials under Nanoindentation: Ryuta Kasada1; Satoshi Konishi1; Hyoseong Gwon1; Takeshi Miyazawa1; Masami Ando1; Hiroyasu Tanigawa1; 1Kyoto University
    Nanoindentation hardness test as well as nanoindentation micro-pillar compression test have been widely used for evaluating irradiation hardening behavior of ion-irradiated materials and the obtained results are discussed with microstructural evolution under ion-irradiation in the subsurface up to several micron meters. Previously we classified and clarified factors, such as indentation size effect, damage gradient effect, and softer substrate effect, controlling nanoindentation hardness of ion-irradiated materials and developed a useful methodology to evaluate a "bulk-equivalent" hardness which can be related to Vickers hardness. However the obtained hardness results are still under consideration because of the complex deformation behavior under nanoindentation testing. Micro-pillar compression test also shows size-dependent deformation behavior. This study investigates the deformation behavior of ion-irradiated materials during nanoindentation tests experimentally and the results are discussed with finite element analysis.

11:10 AM  
Characterizing Radiation Damage in Stainless Steels Using Spherical Nanoindentation Stress-Strain Curves: Jordan Weaver1; Siddhartha Pathak2; Ashley Reichardt3; Peter Hosemann3; Nathan Mara1; 1Los Alamos National Laboratory; 2University of Nevada Reno; 3University of California Berkeley
    Recent spherical nanoindentation and electron backscatter diffraction protocols have proven capable of capturing the grain-scale mechanical anisotropy and subtle changes in mechanical behavior in a variety of metallic materials including the mechanical effects of ion irradiation. The grain-scale response is captured in the form of an indentation stress-strain curve which reliably quantifies the elastic, elastic-plastic transition, and hardening behavior. A systematic study of ion and neutron irradiated austenitic stainless steel samples was conducted to validate spherical nanoindentation protocols for assessing the mechanical effects of radiation damage. For example, an increase in indentation yield strength of ~1.7 and, surprisingly, an increase in the early indentation hardening rate is seen for proton irradiated (max of 10 dpa, 25°C) 304 stainless steel. These findings and the implications for high throughput characterization of new alloys for nuclear applications will be presented and discussed.

11:30 AM  
Novel Methods of Recording Flow Curves in Proton Irradiated Material: Albert Smith1; Jack Donoghue1; Bartlomiej Winiarski1; Alistair Garner1; Nick Riddle2; Keith Wilford2; Philip Withers1; Michael Preuss1; 1University of Manchester; 2Rolls-Royce
    Using proton damage as a surrogate for neutron damage is attractive due to an increased displacement rate resulting in significant time and financial savings. However, the limited penetration of protons, in the order of a few tens of microns in millimeter thick samples, complicates studies probing standard mechanical properties that go beyond hardness testing. This project explores two solutions to this issue. Firstly, Xenon-based Plasma FIB micro-machining has been used to produce micro tensile samples with bulk representative cross section of grains in sufficiently small grained material enabling the direct recording of stress-strain curves from proton-irradiated material. Secondly, by combining XRD-based stress analysis and digital image correlation during tensile loading of standard tensile samples with a proton-irradiated layer has been applied to reconstruct stress-strain curves with the load information only recorded from the surface region. The two techniques are validated against each other and discussed.

11:50 AM  Invited
Small Scale Mechanical Testing on He Bubble Containing and Irradiated Materials: Peter Hosemann1; Zhangjie Wang1; David Frazer1; Frances Allen1; 1University of California Berkeley
    The development of small scale mechanical testing has opened a large number of opportunities to evaluate material properties for both ion-beam and neutron irradiated materials. Recent developments in ion beam microscopy allowed to use ion beam microscopes to induce He bubbles and radiation damage in materials at a local scale enabling multiple dose implantations within the same grain. Combining the capability of small scale mechanical testing and ion beam microscopy revealed itself as a powerful tool to study the effect of He bubbles on mechanical properties. It is found that He bubble superlattices can be induced in tested metals and a significant change of the mechanical properties was observed. The change in properties as a function of implantation parameters and aging time is investigated while the question of how the He bubble superlattice changes during the plastic deformation is raised and answered in this work.