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Now showing items 1 - 16 of 39

  • Ion irradiation effects on commercial PH 13-8 Mo maraging steel Corrax

    Zheng, Ce   Schoell, Ryan   Hosemann, Peter   Kaoumi, Djamel  

    The effects of irradiation on the precipitation behavior of commercial PH 13-8 Mo maraging steel a.k.a. Corrax are investigated through in-situ ion irradiation. Samples of the alloy in its solution annealed state are irradiated up to 10 dpa at 573 and 773 K using 1 MeV Kr ions, in-situ in a transmission electron microscope in order to probe irradiation effects on the precipitation usually observed in this alloy under thermal aging. Indeed, the alloy is known to develop a relatively fine distribution of precipitates during thermal aging which gives the martensitic alloy its strength. The effects of irradiation are substantiated by comparing with the same material thermally aged at 773 and 873 K for similar amounts of experimental time. Both radiation and thermal aging induced segregation and precipitation are characterized using analytical transmission electron microscopy (TEM) techniques. The diffusion coefficients under irradiation are estimated using the point defect balance equations based on Rate Theory and then compared with the thermal diffusion coefficients, demonstrating the accelerated precipitation of beta-phase and Laves-phase in the irradiation case at relatively lower temperature is attributed to the radiation-enhanced diffusion. In addition, a numerical model based on classical precipitate nucleation and growth theories is introduced and shows a relatively good agreement with the experimental results in terms of precipitate density. This study serves to generate baseline data on ion irradiation effects on Corrax to learn how this steel responds to irradiation. (C) 2018 Elsevier B.V. All rights reserved.
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  • In situ small-scale mechanical testing under extreme environments

    Barnoush, Afrooz   Hosemann, Peter   Molina-Aldareguia, Jon   Wheeler, Jeffrey M.  

    The high precision offered by small-scale mechanical testing has allowed the relationships between mechanical behavior and specific microstructural features to be determined to an unprecedented degree. However, of most interest to scientists and engineers is often the behavior of materials under service conditions in an extreme environment, such as high/low temperatures, high strain rates, hydrogen atmosphere, or radiation. In this article, we detail progress made to adapt nanomechanical testing systems and techniques to observe materials behavior in situ in extreme environments.
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  • Ion irradiation effects on commercial PH 13-8 Mo maraging steel Corrax

    Zheng, Ce   Schoell, Ryan   Hosemann, Peter   Kaoumi, Djamel  

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  • Advanced Characterization and Testing of Irradiated Materials

    Bhattacharyya, Dhriti   Zhang, Fan   Hosemann, Peter  

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  • Oxidation Kinetics of Ferritic Alloys in High-Temperature Steam Environments

    Parker, Stephen S.   White, Josh   Hosemann, Peter   Nelson, Andrew  

    High-temperature isothermal steam oxidation kinetic parameters of several ferritic alloys were determined by thermogravimetric analysis. The oxidation kinetic constant (k) was measured as a function of temperature from 900A degrees C to 1200A degrees C. The results show a marked increase in oxidation resistance compared to reference Zircaloy-2, with kinetic constants 3-5 orders of magnitude lower across the experimental temperature range. The results of this investigation supplement previous findings on the properties of ferritic alloys for use as candidate cladding materials and extend kinetic parameter measurements to high-temperature steam environments suitable for assessing accident tolerance for light water reactor applications.
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  • An Electrochemical Impedance Spectroscopic Study of Oxide Films in Liquid Metal

    Qiu, Jie   Macdonald, Digby D.   Li, Nan   Schoell, Ryan   Kaoumi, Djamel   Hosemann, Peter  

    Electrochemical impedance spectroscopy (EIS) is a powerful technique for the non-destructive, dynamic measurement of electrochemical corrosion behavior in condensed environments, and is a demonstrated, in situ method for monitoring oxide films formed on metal surfaces in liquid metals. To characterize this capability, the impedance properties of three kinds of oxide films (anodic titanium oxide films, deposited Fe2O3 films, and thermally oxidized Fe samples) in liquid metals were examined using the EIS technique. The results show that the impedance response is related to the oxide film thickness and quality. The impedance of thin oxide films (< 50 nm thick) in liquid lead-bismuth eutectic (LBE) is negligible, while the EIS of thicker oxide films (> 200 nm) shows that the oxide film without cracks is stable in LBE and protects the substrate from corrosion. EIS is a promising method for accessing the electrochemical behavior of oxide films on metals and alloys in liquid metals.
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  • Nanomechanical Measurements in Harsh Environments

    Hosemann, Peter   Li, Xiaodong  

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  • Fabrication and thermo-mechanical behavior of ultra-fine porous copper

    Kreuzeder, Marius   Abad, Manuel-David   Primorac, Mladen-Mateo   Hosemann, Peter   Maier, Verena   Kiener, Daniel  

    Porous materials with ligament sizes in the submicrometer to nanometer regime have a high potential for future applications such as catalysts, actuators, or radiation tolerant materials, which require properties like high strength-to-weight ratio, high surface-to-volume ratio, or large interface density as for radiation tolerance. The objective of this work was to manufacture ultra-fine porous copper, to determine the thermo-mechanical properties, and to elucidate the deformation behavior at room as well as elevated temperatures via nanoindentation. The experimental approach for manufacturing the foam structures used high pressure torsion, subsequent heat treatments, and selective dissolution. Nanoindentation at different temperatures was successfully conducted on the ultra-fine porous copper, showing a room temperature hardness of 220 MPa. During high temperature experiments, oxidation of the copper occurred due to the high surface area. A model, taking into account the mechanical properties of the copper oxides formed during the test, to describe the measured mechanical properties in dependence on the proceeding oxidation was developed. The strain rate sensitivity of the copper foam at room temperature was similar to 0.03 and strongly correlated with the strain rate sensitivity of ultra-fine grained bulk copper. Although oxidation occurred near the surface, the rate-controlling process was still the deformation of the underlying copper. An increase in the strain rate sensitivity was observed, comparably to that of ultrafine-grained copper, which can be linked to thermally activated processes at grain boundaries. Important insights into the effects of oxidation on the deformation behavior were obtained by assessing the activation volume. Oxidation of the ultra-fine porous copper foam, thereby hindering dislocations to exit to the surface, resulted in a pronounced reduction of the apparent activation volume from similar to 800 to similar to 50 b(3), as also typical for ultra-fine grained materials.
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  • Compatibility studies on Mo–Coating systems for nuclear fuel cladding applications

    Hosemann, Peter   Koh, Huan Chin   Chou, Peter   Glaeser, Andreas M.   Cionea, Cristian  

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  • Key mechanistic features of swelling and blistering of helium-ion-irradiated tungsten

    Allen, Frances I.   Hosemann, Peter   Balooch, Mehdi  

    Helium-ion-induced swelling and blistering of single-crystal tungsten is investigated using a Helium Ion Microscope for site-specific dose-controlled irradiation (at 25 keV) with analysis by Helium Ion Microscopy, Atomic Force Microscopy and Transmission Electron Microscopy (cross-sectioning by Focused Ion Beam milling). We show that the blister cavity forms at a depth close to the simulated helium peak and that nanobubbles coalesce to form nanocracks within the envelope of the ion stopping range, swelling the blister shell. These results provide the first direct experimental evidence for the interbubble fracture mechanism proposed in the framework of the gas pressure model for blister formation. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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  • Small-Scale Testing of In-Core Fast Reactor Materials

    HOSEMANN, Peter   DAI, Yong   STERGAR, Erich   NELSON, Andrew T.   MALOY, Stuart A.  

    Part of the Fuel Cycle R&D (FCRD) initiative in the USA is to investigate materials for high dose application. While mechanical testing on large samples delivers direct engineering data, these types of tests are only possible if enough sample material and required hot cell capabilities are available. Small-scale materials testing methods in addition to large-scale materials testing allows insight on the same specimen and direct probing into areas of interest which are not accessible otherwise. In order to establish an empirical and research-based relationship between small-scale and large-scale materials testing, several different mechanical testing techniques were conducted on the same specimen irradiated in the Swiss spallation source irradiation program (STIP) at the Swiss spallation source (SINQ) at the Paul Scherrer Institute (PSI) up to a dose of 19 dpa. It is shown that the yield strength measured by tensile testing, microcompression testing and microhardness testing all show the same trend. In addition, focused ion beam (FIB)-based techniques also are used to produce local electrode atom probe (LEAP) samples. This procedure allows cutting samples of such a small size that no radioactivity on the prepared sample can be measured.
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  • Nanostructured Engineering Alloys for Nuclear Application

    Hosemann, Peter   Stergar, Erich   Nelson, Andrew T.   Vieh, C.   Maloy, Stuart A.  

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  • Studying Radiation Damage in Structural Materials by Using Ion Accelerators

    Hosemann, Peter  

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  • Atom probe tomography analysis of high dose MA957 at selected irradiation temperatures

    Bailey, Nathan A.   Stergar, Erich   Toloczko, Mychailo   Hosemann, Peter  

    Oxide dispersion strengthened CODS) alloys are meritable structural materials for nuclear reactor systems due to the exemplary resistance to radiation damage and high temperature creep. Summarized in this work are atom probe tomography (APT) investigations on a heat of MA957 that underwent irradiation in the form of in-reactor creep specimens in the Fast Flux Test Facility Materials Open Test Assembly (FFTF-MOTA) for the Liquid Metal Fast Breeder Reactor (LMFBR) program. The oxide precipitates appear stable under irradiation at elevated temperature over extended periods of time. Nominally, the precipitate chemistry is unchanged by the accumulated dose; although, evidence suggests that ballistic dissolution and reformation processes are occurring at all irradiation temperatures. At 412 degrees C-109 dpa, chromium enrichments - consistent with the alpha' phase - appear between the oxide precipitates, indicating radiation induced segregation. Grain boundaries, enriched with several elements including nickel and titanium, are observed at all irradiation conditions. At 412 degrees C-109 dpa, the grain boundaries are also enriched in molecular titanium oxide (TiO). (C) 2015 Elsevier B.V. All rights reserved.
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  • Nanomechanical Characterization of the Tensile Modulus of Rupture for Kerogen-Rich Shale

    Hull, Katherine L.   Abousleiman, Younane N.   Han, Yanhui   Al-Muntasheri, Ghaithan A.   Hosemann, Peter   Parker, S. Scott   Howard, Cameron B.  

    In the past decade, chemical, physical, and mechanical characterization of source-rock reservoirs has moved toward micro-and nanoscale testing and analyses. Nanoindentation is now widely used in many industrial and university laboratories to measure stiffness and strength as well as other mechanical properties of shales. However, to date, tensile failures of shales have not been studied at the micro-or nanoscale. In this work, a scanning electron microscope (SEM) coupled with a focused ion beam (FIB) and a special nanoindenter (NI) testing configuration (SEM-FIB-NI) is used to bring organic-rich shale samples (preserved Woodford shale from a wellsite in Ada, Oklahoma, USA) to failure in tension. Microcantilever beam geometries were milled and loaded to failure in tension while monitoring in situ with SEM. The force-displacement curves were generated while videos recording in-situ real-time displacements and failures were collected simultaneously. The microcantilever beam tests of this composite natural material demonstrate linear elastic behavior followed by elastic/plastic yield before complete failure. This behavior was clearly observed to correlate with the amount of organic matter (OM) at the fractured surface of the microcantilever beam supports. Energy-dispersive X-ray spectroscopy (EDS) analyses were conducted along the prepared microbeam samples before loading. In addition, post-failure EDS analysis was performed on the resulting fractured faces of the failed microbeams, and the correlation between tensile behavior and shale OM content was shown. Large tensile moduli of rupture, or moduli of toughness, were associated with high OM, or kerogen, present at the failed supports of the kerogen-rich-shale (KRS) microcantilever beams. The moduli of toughness as a measure of work or energy needed to bring these samples into tensile failure were ten times less when OM was missing or barely present at the support, in terms of shale microbeam volume.
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  • Effects of applied strain on radiation damage generation in body centered cubic iron

    Beeler, Benjamin   Asta, Mark   Hosemann, Peter   Gronbech-Jensen, Niels  

    Radiation damage in body-centered cubic (BCC) Fe has been extensively studied by computer simulations to quantify effects of temperature, impinging particle energy, and the presence of extrinsic particles. However, limited investigation has been conducted into the effects of mechanical stresses and strain. In a reactor environment, structural materials are often mechanically strained, and an expanded understanding of how this strain affects the generation of defects may be important for predicting microstructural evolution and damage accumulation under such conditions. In this study, we have performed molecular dynamics simulations in which various types of homogeneous strains are applied to BCC Fe and the effect on defect generation is examined. It is found that volume-conserving shear strains yield no statistically significant variations in the stable number of defects created via cascades in BCC Fe. However, strains that result in volume changes are found to produce significant effects on defect generation. (C) 2015 Elsevier B.V. All rights reserved.
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