Accelerated Materials Evaluation for Nuclear Applications Utilizing Irradiation and Integrated Modeling: Current and Advanced Structural Materials I
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Assel Aitkaliyeva, University of Florida; Peter Hosemann, University of California - Berkeley; Samuel Briggs, Oregon State University; David Frazer, Los Alamos National Laboratory

Wednesday 2:00 PM
February 26, 2020
Room: Theater A-8
Location: San Diego Convention Ctr

Session Chair: David Frazer, Los Alamos National Laboratory

2:00 PM
Microstructure of HT-9 Cladding After fuel-cladding Chemical Interaction with an Annular U-10Zr Fuel Irradiated to 3.3% FIMA: Xiang Liu¹; Luca Capriotti¹; Tiankai Yao¹; Jason Harp¹; Lingfeng He¹; ¹Idaho National Laboratory
    U-Zr fuel and ferritic/martensitic HT-9 cladding is the primary fuel system for fast reactors. Although a low smear density (~75%) was often employed to avoid the premature mechanical failure of the cladding, fuel swelling eventually brings the fuel and cladding into contact and leads to fuel-cladding chemical interaction (FCCI). FCCI is a limiting factor that restricts the fuel performance at high burnups. Annual fuel forms are being investigated due to their advantages in back end fuel cycle. Here, we investigated the FCCI layer and nearby cladding regions of an annular U-10Zr fuel with HT-9 cladding irradiated to 3.3% FIMA. Significant amount of fission products diffused into the cladding and formed intergranular precipitates, whereas the outgoing C diffusion led to decarbonization of the cladding. In the FCCI layer, a fine-grained U,Fe-rich phase (wastage), with a high number density of ~15 nm intragranular voids and ~50 nm intergranular voids was found.

2:20 PM
Development of Advanced Low N-12Cr (wt.%) Ferritic/Martensitic Steel for Reactor Applications: Connor Rietema¹; Tarik Saleh²; Benjamin Eftink²; Stuart Maloy²; Osman Anderoglu³; Md Mehadi Hassan³; Amy Clarke¹; Kester Clarke¹; ¹Colorado School of Mines; ²Los Alamos National Laboratory; ³University of New Mexico
    Low nitrogen (<10 wppm) vacuum-induction melted (VIM) lab heats of the ferritic/martensitic alloy HT-9 have shown significant resistance to ductility loss after low temperature (<0.3 Tm) irradiation. Here we examine the role of interstitial nitrogen on the effect of ductility loss after low temperature irradiation. Interstitial nitrogen levels are controlled by strategic titanium or zirconium microalloy additions. High nitrogen (440 wppm) and low nitrogen (10 wppm) VIM heats, along with four heats containing various levels of titanium and one zirconium-containing heat, have been produced. Following initial characterization of the interstitial nitrogen levels in each alloy utilizing time-of-flight secondary ion mass spectrometry (TOF-SIMS) and internal friction measurements, proton irradiation at 300 ˚C to low dpa and subsequent characterization of the irradiated microstructures and properties was performed.

2:40 PM  Cancelled
Promotion and Suppression of the G-phase in Steels: Daniel King¹; Thomas Whiting¹; Mark Wenman¹; ¹Imperial College London
    Solute clustering and G-phase precipitation cause hardening phenomena observed in low alloy reactor pressure vessel steels and duplex steels for coolant piping. Density functional theory was used to make a comparison of 22 different G-phase compositions. The Mn₆Ni₁₆Si₇ composition was found to have the most similar elastic properties to α-Fe. Further investigation into the effect of solute species 14 elements on the formation of the Mn-Ni-Si G-phase in a ferrite matrix was made. Many species known to cluster with Mn, Ni and Si were also found to stabilise the G-phase structure. A comparison in formation enthalpy between the G-phase and body centred cubic structure was made for Fe-Mn-Ni-Si compositions to assess the site preference of Fe when in high concentrations.

3:00 PM
Temperature Shift Evaluation for G-phase Clustering in Ferritic-martensitic Alloys: Matthew Swenson¹; Saheed Adisa¹; ¹University of Idaho
    The objective of this study is to evaluate the temperature shift requirement for high dose-rate ion irradiation to accurately emulate low dose-rate neutron irradiation in three ferritic-martensitic alloys. Historically, the temperature shift for using ion irradiations has been determined using the invariance theory, particularly for defect cluster evolution. However, it is unclear if the invariance theory also applies for solute cluster evolution. We have systematically characterized the size evolution of Si-Mn-Ni-rich nanoclusters in the ferritic-martensitic alloys HCM12A, HT9, and T91 following irradiations to 3 dpa at 500°C with either Fe2+ ions or neutrons. Two unique models each predict that Fe2+ ion irradiation at ~370°C will more accurately emulate G-phase evolution resulting from neutron irradiation at 500°C, representing a negative temperature shift. We have conducted the prescribed Fe2+ ion irradiation at 370°C to 3 dpa for comparison with neutron irradiation to 3 dpa at 500°C and will present the results.

3:20 PM
Effective Defect Sinks in Metallic Composite with Nanodispersoids: In situ Ion Radiation Transmission Electron Microscopy and Position Annihilation Lifetime Spectroscopy: Kangpyo So¹; Ming Liu²; Mohammad Shahin¹; Myles Stapelberg¹; So Yeon Kim¹; Michael Short¹; Ju Li¹; ¹Massachusetts Institute of Technology; ²North Carolina State University
    The accumulation of defects during irradiation leads to material property degradation modes such as embrittlement and swelling, eventually causing material failure. Effective and efficient removal of defects is of crucial importance to design radiation damage-tolerant materials. Here, by biasing defect migration pathways via carbon nanotube (CNT) infiltration, we present a greatly enhanced damage-tolerant metal-CNT composite with defect storage measured to be one order of magnitude lower than that in pure, irradiated Al. In situ ion irradiation transmission electron microscopy (TEM) experiments and atomistic simulations together reveal the dynamic evolution and convergent diffusion of radiation-induced defects to CNTs, facilitating defect recombination and enhancing radiation tolerance. The occurrence of CNT-biased defect convergent migration is tuned by the thermodynamic driving force of the stress gradient in the Al matrix due to the CNT phase transformation. Further positron annihilation lifetime spectroscopy of nano-dispersion will be discussed to verify the defect annihilation mechanism.

3:40 PM Break

3:55 PM
On a Theory Based Accelerated Testing Methodology for Swelling: Michael Fluss¹; ¹University of California, Berkeley, Department of Nuclear Engineering
    Failure to accurately account for the effects of dose rate have inhibited the utilization of heavy ion beam induced accelerated radiation damage accumulation as a reliable engineering predictor of reactor neutron damage accumulation. We will outline an experimental methodology where heavy-ion induced swelling alone is a predictor of neutron induced swelling, yielding a swelling equation that is a function of dpa, dpa-rate, and temperature, and spanning 10^-2 to 10^-8 dpa/s. Moreover, we will show how the key experimentally measurable characteristics of the swelling curve (peak-temperature, shape, and swelling-per-dpa) are all tied to existing rate theory through log functions of the dpa-rate. The proposed methodology has the potential to reduce risks and uncertainties associated with life extension and new material development.

4:15 PM
Controlling Helium Morphology in Pure Metals: Toward Uniform Samples for the Accelerated Measurement of Bulk Irradiated Properties: Calvin Lear¹; Saryu Fensin¹; ¹Los Alamos National Laboratory
    Prolonged irradiation of structural metals results in the formation of excess microstructural defects, increased maintenance costs, and diminished confidence in components. The evolution of helium content and morphology are key to this form of aging, yet the ways in which helium impacts materials strength are only partially understood. A systematic study was thus performed on α-Ti and Cu implanted at various temperature-dose-dose rate conditions. Implanted samples were characterized using electron microscopy and micro-mechanical testing to determine stable conditions for the formation of atomic clusters, spherical bubbles, and faceted bubbles of helium in the model HCP and FCC metals. Helium morphologies (i.e., feature type, size, and density) are considered in terms of nucleation and growth control, the viability of implanting them uniformly throughout micro-scale test specimens (i.e., > 100 μm), and their consequences for materials strength.

4:35 PM
Defect Evolution and Radiation Resistance of Advanced Fusion Materials Under Heavy Ion and Low Energy Helium Irradiation: Osman El-Atwani¹; Stuart Maloy¹; ¹Los Alamos National Laboratory
    The degradation of the morphology and mechanical properties of helium and neutron irradiated tungsten stimulated recent research on the discovery of new and irradiation resistant plasma facing and structural materials for fusion power. Here we present a summary of the performance of nanocrystalline W and ultrafine W-TiC alloys under heavy ion (to simulate neutron damage) and low energy helium (to simulate transmutation reactions) irradiation performed in-situ in the TEM. Defect (dislocation loops and bubbles) evolution (density, size and total damage) as a function of time (dose) is illustrated. Conclusions were supported from the in-situ irradiation/TEM videos where the dynamic response (defect dynamics) is observed directly. Interpretation of the experimental results with theory is made and emphasized the need of advanced modeling and simulations to fundamentally understand the performance of these materials and design radiation resistant fusion materials.

4:55 PM
In-situ Heavy Ion Irradiation of FCC and BCC High-entropy Alloys at Cryogenic and High Temperatures: Calvin Parkin¹; Michael Moorehead¹; Mohamed Elbakhshwan¹; Jing Hu²; Wei-Ying Chen²; Kumar Sridharan¹; Adrien Couet¹; ¹University of Wisconsin, Madison; ²Argonne National Laboratory
    In-core structural materials for SFR cladding are expected to demonstrate radiation tolerance up to several hundreds of displacements per atom (dpa) over the operating lifetime. High-entropy alloys (HEA) consisting of four or more principle alloying elements in single-phase solid solution are theorized to resist radiation due to unique energy and mass transport properties. The dependence of microstructural evolution on irradiation temperature and compositional complexity is expected to reveal these radiation tolerance mechanisms. In situ heavy-ion irradiation experiments up to 2 dpa were performed at the IVEM facility at ANL. HEA from the CrFeMnNi (FCC) and NbTaTiV (BCC) families, whose phase evolutions were modeled by CALPHAD, were compared to less compositionally complex reference materials at irradiation temperatures of 50K, 300K, and 773K. Small defect clusters and prismatic loops were observed and quantified in all alloys as function of dose and temperature. The effect of compositional complexity on irradiation response is discussed.

5:15 PM  Cancelled
Interphase Distribution Behavior of Oxide Nanoparticles Triggered by Isothermal Ferrite Transformation in 9Cr ODS Steels: Xiaosheng Zhou¹; Hao Chen¹; ¹Tsinghua University
    By performing isothermal ferrite transformation, the interphase distribution of oxide nanoparticles in 9Cr ODS steels is attained for the first time. The ferrite transformation kinetics and resultant microstructure characteristics are examined in detail by dilatometry, EBSD, SEM and TEM measurements. The oxide size, sheet spacing and lattice planes of oxide sheets have been analyzed. The oxide interphase distribution behavior exhibits similarities and difference with the conventional carbide interphase precipitation, and the mobility of ferrite/austenite interphase boundaries is suggested to have a significant effect on the formation of oxide interphase distribution. Two possible mechanisms are proposed to explain the oxide distribution: dissolution-re-precipitation mechanism and phase-boundary dragging particle mechanism.