The mechanism behind the high radiation tolerance of Fe-Cr alloys
}, volume={131}, ISSN={["1089-7550"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85127675955&partnerID=MN8TOARS}, DOI={10.1063/5.0085086}, abstractNote={Fe–Cr alloys are at the forefront for high radiation tolerant materials with long-standing validated performance. Yet, the detailed mechanism behind their high radiation resistance is in question and understanding the effect of varying Cr percentage is a grand challenge limiting further improvements. Here, we applied depth-resolved positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy to study the effect of Cr alloying on the formation and evolution of atomic size clusters induced by ion-irradiation in Fe. We also used atom probe tomography to investigate the possible presence of Cr clusters or α′ phase precipitates with high Cr composition. The study reveals that the well-known resistance to radiation in Fe–Cr alloys may arise from the stabilization of vacancy clusters around Cr atoms, which act as sinks for radiation-induced defects. This implies that Cr atoms do not provide a direct sink for interstitials; rather defect complexes that consist of Cr atoms and vacancies, in turn, act as sinks for irradiation-induced vacancies and interstitials. we also find that lower amounts of Cr create smaller defect clusters that act as efficient sinks for radiation damage, but larger quantities of Cr form a defect structure that is less homogenous and larger in size, resulting in less efficient damage recombination. No evidence of α′ was found before or after irradiation, which indicates that it does not contribute to the observed radiation tolerance.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Agarwal, S. and Butterling, M. and Liedke, M. O. and Yano, K. H. and Schreiber, D. K. and Jones, A. C. L. and Uberuaga, B. P. and Wang, Y. Q. and Chancey, M. and Kim, H. and et al.}, year={2022}, month={Mar} } @article{auguste_chan_romanovskaia_qiu_schoell_liedke_butterling_hirschmann_attallah_wagner_et al._2022, title={A multimodal approach to revisiting oxidation defects in Cr2O3}, volume={6}, ISSN={["2397-2106"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85134822843&partnerID=MN8TOARS}, DOI={10.1038/s41529-022-00269-7}, abstractNote={AbstractThe oxidation of chromium in air at 700 °C was investigated with a focus on point defect behavior and transport during oxide layer growth. A comprehensive set of characterization techniques targeted characteristics of chromium oxide microstructure and chemical composition analysis. TEM showed that the oxide was thicker with longer oxidation times and that, for the thicker oxides, voids formed at the metal/oxide interface. PAS revealed that the longer the oxidation time, there was an overall reduction in vacancy-type defects, though chromium monovacancies were not found in either case. EIS found that the longer oxidized material was more electrochemically stable and that, while all oxides displayed p-type character, the thicker oxide had an overall lower charge carrier density. Together, the results suggest anion oxygen interstitials and chromium vacancy cluster complexes drive transport in an oxidizing environment at this temperature, providing invaluable insight into the mechanisms that regulate corrosion.}, number={1}, journal={NPJ MATERIALS DEGRADATION}, author={Auguste, R. and Chan, H. L. and Romanovskaia, E. and Qiu, J. and Schoell, R. and Liedke, M. O. and Butterling, M. and Hirschmann, E. and Attallah, A. G. and Wagner, A. and et al.}, year={2022}, month={Jul} } @article{schoell_kabel_lam_sharma_michler_hosemann_kaoumi_2022, title={Corrosion behavior of a series of combinatorial physical vapor deposition coatings on SiC in a simulated boiling water reactor environment}, volume={572}, ISSN={["1873-4820"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85138461418&partnerID=MN8TOARS}, DOI={10.1016/j.jnucmat.2022.154022}, abstractNote={The simulated boiling water condition corrosion properties of multilayer and combinatorial physical vapor deposition metal coatings (Zr, Cr, and/or Ti) deposited on a SiCf-SiC composite were investigated. Various compositions within the ternary system were corroded to the most suitable composition preventing underlying SiCf-SiC from further attack. Mass measurements and visual observations were conducted to identify which coatings formed protective oxides and which coatings spalled. Transmission electron microscopy was conducted to observe the microstructure of the physical vapor deposition metal layer before and after corrosion as well as identify the oxide which were forming.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Schoell, Ryan and Kabel, Joey and Lam, Sebastian and Sharma, Amit and Michler, Johann and Hosemann, Peter and Kaoumi, Djamel}, year={2022}, month={Dec} } @article{hong_morales_chan_macdonald_balooch_xie_romanovskaia_scully_kaoumi_hosemann_2022, title={Effect of thermal oxidation on helium implanted 316L stainless steel}, volume={132}, ISSN={["1089-7550"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85144284308&partnerID=MN8TOARS}, DOI={10.1063/5.0122487}, abstractNote={The effect of thermal oxide layer on He implanted 316L stainless steel was studied to evaluate experimentally how thermal oxidation affects the diffusion and distribution of He in the material. In the case of thermal oxidation of a He implanted sample, with an increase in oxidation time, the max swelling height increases logarithmically as a function of time and finally saturates for all samples except for the lowest dose of implanted He. Concerning TEM results, two void regions are identified. Similar to the calculation, the total irradiated depth was around 250 nm and the large void region was formed around 100–150 nm depth. On the other hand, the small void region was observed immediately under oxide layer from the thermal oxidation. In contrast, there were no voids in the altered zone near the metal/oxide interface in the non-thermal oxidized/He implanted sample. This description of the phenomena was justified using the Kirkendall effect and the Point Defect Model.}, number={18}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hong, Minsung and Morales, Angelica Lopez and Chan, Ho Lun and Macdonald, Digby D. and Balooch, Mehdi and Xie, Yujun and Romanovskaia, Elena and Scully, John R. and Kaoumi, Djamel and Hosemann, Peter}, year={2022}, month={Nov} } @inproceedings{schoell_dejong_alarcon_zheng_frazer_hosemann_kaoumi_2022, title={In Situ Ion Irradiation and Compression of Micropillars inside a Transmission Electron Microscope .}, url={https://www.osti.gov/biblio/2006391}, DOI={10.2172/2006391}, author={Schoell, Ryan; and DeJong, Matt; and Alarcon, Phillip; and Zheng, Ce; and Frazer, David; and Hosemann, Peter; and Kaoumi, Djamel}, year={2022}, month={Oct} } @article{schoell_xi_west_hosemann_park_kenesei_almer_shayer_kaoumi_2022, title={Investigation of the fatigue crack behavior of 304 stainless steels using synchrotron X-ray tomography and diffraction: Influence of the martensite fraction and role of inclusions}, volume={188}, ISSN={["1873-4189"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85129349891&partnerID=MN8TOARS}, DOI={10.1016/j.matchar.2022.111903}, abstractNote={The effect of fatigue on the microstructure of four-point bend specimens of three variations of 304 stainless steels (Commercial 304, 304H, and 304 L) was investigated using synchrotron x-ray tomography and diffraction. X-ray tomography revealed the formation of the fatigue-induced microvoids and crack while the diffraction data was used to quantify the amount of deformation-induced martensite found after fatigue in all samples. Transmission electron microscopy evidenced the role of the precipitates/inclusions on the microvoid formation. It was found to depend on their chemical nature. The shape of the precipitates/inclusions was also found to have an effect on the microvoid shape.}, journal={MATERIALS CHARACTERIZATION}, author={Schoell, Ryan and Xi, Li and West, Harvey and Hosemann, Peter and Park, Jun-Sang and Kenesei, Peter and Almer, Jonathan and Shayer, Zeev and Kaoumi, Djamel}, year={2022}, month={Jun} } @article{horn_rock_kaoumi_anderson_white_prost_rieken_saptarshi_schoell_dejong_et al._2022, title={Laser Powder Bed Fusion Additive Manufacturing of Oxide Dispersion Strengthened Steel Using Gas Atomized Reaction Synthesis Powder}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85127703398&partnerID=MN8TOARS}, journal={SSRN}, author={Horn, T. and Rock, C. and Kaoumi, D. and Anderson, I. and White, E. and Prost, T. and Rieken, J. and Saptarshi, S. and Schoell, R. and DeJong, M. and et al.}, year={2022} } @article{saptarshi_dejong_rock_anderson_napolitano_forrester_lapidus_kaoumi_horn_2022, title={Laser Powder Bed Fusion of ODS 14YWT from Gas Atomization Reaction Synthesis Precursor Powders}, volume={8}, ISSN={["1543-1851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85135355752&partnerID=MN8TOARS}, DOI={10.1007/s11837-022-05418-6}, abstractNote={AbstractLaser powder bed fusion (LPBF) additive manufacturing (AM) is a promising route for the fabrication of oxide dispersion strengthened (ODS) steels. In this study, 14YWT ferritic steel powders were produced by gas atomization reaction synthesis (GARS). The rapid solidification resulted in the formation of stable, Y-containing intermetallic Y2Fe17 on the interior of the powder and a stable Cr-rich oxide surface. The GARS powders were consolidated with LPBF. Process parameter maps identified a stable process window resulting in a relative density of 99.8%. Transmission electron microscopy and high-energy x-ray diffraction demonstrated that during LPBF, the stable phases in the powder dissociated in the liquid melt pool and reacted to form a high density (1.7 × 1020/m3) of homogeneously distributed Ti2Y2O7 pyrochlore dispersoids ranging from 17 to 57 nm. The use of GARS powder bypasses the mechanical alloying step typically required to produce ODS feedstock. Preliminary mechanical tests demonstrated an ultimate tensile and yield strength of 474 MPa and 312 MPa, respectively.}, journal={JOM}, author={Saptarshi, Sourabh and DeJong, Matthew and Rock, Christopher and Anderson, Iver and Napolitano, Ralph and Forrester, Jennifer and Lapidus, Saul and Kaoumi, Djamel and Horn, Timothy}, year={2022}, month={Aug} } @article{horn_rock_kaoumi_anderson_white_prost_rieken_saptarshi_schoell_dejong_et al._2022, title={Laser powder bed fusion additive manufacturing of oxide dispersion strengthened steel using gas atomized reaction synthesis powder}, volume={216}, ISSN={["1873-4197"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85127141491&partnerID=MN8TOARS}, DOI={10.1016/j.matdes.2022.110574}, abstractNote={Mechanically alloyed Fe-based alloys with oxide dispersion strengthening have largely dropped out of the marketplace due to high cost related to problems with complex and unreliable processing. Nevertheless, the desirable properties of oxide dispersion strengthened (ODS) steels have motivated research on alternate processing routes aimed at improving processing simplicity and reliability. Powders produced by gas atomization reaction synthesis (GARS) consist of stable Fe-Y intermetallic phases and a Cr surface oxide layer that acts as a chemical reservoir during solid-state processing and heat treatment to form a high density of nano-scale oxides. This research explores the use of Fe GARS powders, with 15 wt% Cr with micro-alloyed additions of 0.15 wt% Y and 0.10% Ti, in laser powder bed fusion (LPBF) additive manufacturing (AM), and evaluates the effectiveness of oxide dispersoid formation in the liquid melt pool. Additional oxygen was introduced by varying the LPBF chamber atmospheres using Ar, Ar + 1 wt% O, Ar + 5 wt% O, and air. Characterization of LPBF consolidated solids demonstrated the formation of a high density of nano-scale Y-Ti oxides in the build microstructures from the GARS precursor powders.}, journal={MATERIALS & DESIGN}, author={Horn, Timothy and Rock, Christopher and Kaoumi, Djamel and Anderson, Iver and White, Emma and Prost, Tim and Rieken, Joel and Saptarshi, Sourabh and Schoell, Ryan and DeJong, Matt and et al.}, year={2022}, month={Apr} } @article{schoell_xi_zhao_wu_hong_yu_kenesei_almer_shayer_kaoumi_2022, title={Mechanism of chlorine-induced stress corrosion cracking of two 304 SS heats in simulated marine environment through in situ X-ray tomography and diffraction: Role of deformation induced martensite and crack branching}, volume={190}, ISSN={["1873-4189"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85132337921&partnerID=MN8TOARS}, DOI={10.1016/j.matchar.2022.112020}, abstractNote={In-situ synchrotron x-ray tomography and diffraction experiments were conducted on two heats of 304SS undergoing chlorine-induced stress-corrosion-cracking (CISCC) in a simulated marine environment. The role of deformation induced martensite on CISCC was investigated through diffraction analysis where no significant amount of martensite was found to form during CISCC, indicating that it may not play a significant role in affecting the process. Tomography combined with stress-intensity analysis revealed the influence of stress-intensity on branching types with single crack growth, micro-branching, and macro-branching. Post experimental electron microscopy characterization revealed the presence of FeCl2, CrCl2, and NiCl2·6H2O compounds at the crack, which infers a dissolution mechanism during the experiment. A dissolution mechanism highlighting the synergy between stress and corrosion was proposed to explain chlorine-induced stress-corrosion-cracking and crack branching.}, journal={MATERIALS CHARACTERIZATION}, author={Schoell, Ryan and Xi, Li and Zhao, Yuchen and Wu, Xin and Hong, Yu and Yu, Zhenzhen and Kenesei, Peter and Almer, Jonathan and Shayer, Zeev and Kaoumi, Djamel}, year={2022}, month={Aug} } @article{beausoleil_parry_mondal_gomez-hurtado_aguiar_kaoumi_kwon_2022, title={Spark Plasma Sintered Monbti Based Multi Principal Element Alloys with Cr, V, and Zr}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85130733691&partnerID=MN8TOARS}, journal={SSRN}, author={Beausoleil, G.L. and Parry, M.E. and Mondal, K. and Gomez-Hurtado, L.R. and Aguiar, J.A. and Kaoumi, D. and Kwon, S.}, year={2022} } @article{beausoleil ii_parry_mondal_kwon_gomez-hurtado_kaoumi_aguiar_2022, title={Spark plasma sintered, MoNbTi-based multi-principal element alloys with Cr, V, and Zr}, volume={927}, ISSN={["1873-4669"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85138797103&partnerID=MN8TOARS}, DOI={10.1016/j.jallcom.2022.167083}, abstractNote={MoNbTi, MoNbTiZr, CrMoNbTiZr, and MoNbTiVZr multi-principal element alloys (MPEAs) were fabricated via spark plasma sintering (SPS) and investigated for use in high-strength applications. The fabrication method by SPS and powder metallurgy differs from those presented in the prior literature, where most MPEAs are fabricated using arc melting (AM) methods. Cryogenic milling was used to maximize potential defect sinks (grain boundaries) for radiation resistance and to increase ultimate tensile strength through the Hall-Petch effect. SPS was chosen for consolidation in order to maintain a fine-grained structure during densification. Each alloy was characterized using x-ray diffraction and scanning electron microscopy for phase identification and compositional homogeneity. The base ternary alloy MoNbTi presented a predominantly single BCC system with minor cubic phases. The introduction of additional alloying elements—Zr, V, and Cr—heightened the phase complexity and increased the fractions of a secondary BCC phase and an HCP phase from Zr. The addition of Cr induced a larger fraction of the Laves phase to form. The addition of V caused the precipitation of small Mo inclusions. Thermodynamic analysis was performed to understand the separation of phases in each alloy. Discrepancies among the phase predictions generated by thermodynamic models, phases previously presented in the literature, and the characterization results suggest that MPEA fabrication methods, especially solid-state methods, require significant investigation to ensure that alloys can remain stable throughout their anticipated service lifetimes.}, journal={JOURNAL OF ALLOYS AND COMPOUNDS}, author={Beausoleil Ii, G. L. and Parry, M. E. and Mondal, K. and Kwon, S. and Gomez-Hurtado, L. R. and Kaoumi, D. and Aguiar, J. A.}, year={2022}, month={Dec} } @article{owusu-mensah_cooper_morales_yano_taylor_schreiber_uberuaga_kaoumi_2022, title={Surprisingly high irradiation-induced defect mobility in Fe3O4 as revealed through in situ transmission electron microscopy}, volume={187}, ISSN={["1873-4189"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85127034818&partnerID=MN8TOARS}, DOI={10.1016/j.matchar.2022.111863}, abstractNote={Radiation-induced defects are expected to change the corrosion kinetics when a material is exposed to a corrosive environment. Characterization of the defects forming under irradiation and their ability to move/diffuse is therefore key to understanding how they impact the corrosion kinetics and possibly mechanisms. For that matter, Fe/Fe3O4 interfaces were irradiated using 1 MeV Kr2+ at temperatures of 273 K (25 °C), 573 K (300 °C) and 773 K (500 °C) to a maximum dose of 10 dpa (as measured in the Fe matrix) in situ in a transmission electron microscope. The evolution of the microstructure was followed as a function of the dose and temperature. The formation of defects was followed in the metal and the oxide as well as at the metal/oxide interface and characterized in terms of size and density. The dynamic observation of the spatial distribution of the defects allowed for a qualitative assessment of the mobility of defects in the oxide as a function of temperature, revealing evidence for enhanced mobility even more so than in the Fe matrix. Mechanisms of induced defect mobility in the spinel are discussed to account for the observations.}, journal={MATERIALS CHARACTERIZATION}, author={Owusu-Mensah, Martin and Cooper, Jacob and Morales, Angelica Lopez and Yano, Kayla and Taylor, Sandra D. and Schreiber, Daniel K. and Uberuaga, Blas Pedro and Kaoumi, Djamel}, year={2022}, month={May} } @article{jublot-leclerc_owusu-mensah_borodin_ribis_largeau_schoell_kaoumi_descoins_mangelinck_gentils_2022, title={Synthesis of Nano-Oxide Precipitates by Implantation of Ti, Y and O Ions in Fe-10%Cr: Towards an Understanding of Precipitation in Oxide Dispersion-Strengthened (ODS) Steels}, volume={15}, ISSN={["1996-1944"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85137262989&partnerID=MN8TOARS}, DOI={10.3390/ma15144857}, abstractNote={The properties of oxide dispersion-strengthened steels are highly dependent on the nature and size distribution of their constituting nano-oxide precipitates. A fine control of the processes of synthesis would enable the optimization of pertinent properties for use in various energy systems. This control, however, requires knowledge of the precise mechanisms of nucleation and growth of the nanoprecipitates, which are still a matter of debate. In the present study, nano-oxide precipitates were produced via the implantation of Y, Ti, and O ions in two different sequential orders in an Fe-10%Cr matrix that was subsequently thermally annealed. The results show that the oxides that precipitate are not necessarily favoured thermodynamically, but rather result from complex kinetics aspects related to the interaction between the implanted elements and induced defects. When Y is implanted first, the formation of nanoprecipitates with characteristics similar to those in conventionally produced ODS steels, especially with a core/shell structure, is evidenced. In contrast, when implantation starts with Ti, the precipitation of yttria during subsequent high-temperature annealing is totally suppressed, and corundum Cr2O3 precipitates instead. Moreover, the systematic involvement of {110} matrix planes in orientation relationships with the precipitates, independently of the precipitate nature, suggests matrix restriction effects on the early stages of precipitation.}, number={14}, journal={MATERIALS}, author={Jublot-Leclerc, Stephanie and Owusu-Mensah, Martin and Borodin, Vladimir A. and Ribis, Joel and Largeau, Ludovic and Schoell, Ryan and Kaoumi, Djamel and Descoins, Marion and Mangelinck, Dominique and Gentils, Aurelie}, year={2022}, month={Jul} } @misc{fang_li_wang_ruiz_ma_wang_zhu_schoell_zheng_kaoumi_et al._2022, title={Achieving high hetero-deformation induced (HDI) strengthening and hardening in brass by dual heterostructures}, volume={98}, ISSN={["1005-0302"]}, url={https://doi.org/10.1016/j.jmst.2021.03.088}, DOI={10.1016/j.jmst.2021.03.088}, abstractNote={Heterostructured materials have a superior combination of strength and ductility, due to their ability to produce hetero-deform induced (HDI) strengthening and hardening. Therefore, achieving high HDI strengthening and hardening is the primary goal for designing heterostructures. Here we report a dual heterostructure in brass that consists of the heterogeneous lamella and gradient structure, fabricated by rolling, partial annealing, and rotationally accelerated shot peening (RASP). The dual heterostructures are able to generate extra interfaces of heterogeneity compared to the single heterostructures, which could lead to higher HDI strengthening and hardening, and a more superior combination of strength and ductility. This finding presents a new pathway to designing heterostructures in metallic materials.}, journal={JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY}, author={Fang, X. T. and Li, Z. K. and Wang, Y. F. and Ruiz, M. and Ma, X. L. and Wang, H. Y. and Zhu, Y. and Schoell, R. and Zheng, C. and Kaoumi, D. and et al.}, year={2022}, month={Jan}, pages={244–247} } @article{zhao_schoell_zheng_cinbiz_frost_an_kaoumi_2021, title={Creep properties of advanced austenitic steel 709 determined through short experiments under in-situ neutron diffraction followed by TEM characterization}, volume={182}, ISSN={["1873-4189"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85118186981&partnerID=MN8TOARS}, DOI={10.1016/j.matchar.2021.111519}, abstractNote={In this study, the creep mechanisms at play in Alloy 709 (Fe-20Cr-25Ni) are investigated by performing short-term creep-type tests under in-situ neutron diffraction experiments. Short tests are performed in the temperature range of 500 to 900 °C under constant load with a load ranging from 50 to 150 MPa. The creep exponent and activation energy are determined using the Bird-Mukherjee-Dorn relation and compared to that obtained from conventional longer creep tests from the literature. Scanning transmission electron microscopy (S/TEM) of the post-creep microstructure indicates that interaction of dislocations with precipitates are a dominant mechanism at play. Furthermore, local elemental mapping indicated chemical segregation at grain boundaries and formation of complex precipitates.}, journal={MATERIALS CHARACTERIZATION}, author={Zhao, Yuchen and Schoell, Ryan and Zheng, Ce and Cinbiz, Mahmut N. and Frost, Matthew and An, Ke and Kaoumi, Djamel}, year={2021}, month={Dec} } @article{qiu_macdonald_schoell_han_mastromarino_scully_kaoumi_hosemann_2021, title={Electrochemical study of the dissolution of oxide films grown on type 316L stainless steel in molten fluoride salt}, volume={186}, ISSN={["1879-0496"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85104668265&partnerID=MN8TOARS}, DOI={10.1016/j.corsci.2021.109457}, abstractNote={The corrosion behavior of oxide films grown on Type 316L stainless steel (SS) in molten FLiNaK (LiF-NaF-KF: 46.5−11.5−42 mol.%) salt was investigated. The results show that the oxide film formed on Type 316L SS is unstable and can only temporarily protect materials from corrosion in molten FLiNaK salt. Based on the electrochemical impedance spectroscopy, the oxide dissolution rate is calculated to be 0.85 nm/h at 700 °C in molten FLiNaK salt. After the oxide film dissolved, Cr and Fe are selective dealloyed from the steel, leading to intergranular corrosion of Type 316L SS in molten fluoride salt.}, journal={CORROSION SCIENCE}, author={Qiu, Jie and Macdonald, Digby D. and Schoell, Ryan and Han, Junsoo and Mastromarino, Sara and Scully, John R. and Kaoumi, Djamel and Hosemann, Peter}, year={2021}, month={Jul} } @article{mcrobie_schoell_kaspar_schreiber_kaoumi_2021, title={In Situ Grain Growth of Nanograined Magnetite under Ion Irradiation at Room Temperature and 500 ℃}, url={https://www.osti.gov/biblio/1992908}, DOI={10.1017/s1431927621009351}, abstractNote={An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.}, journal={Microscopy and Microanalysis}, author={McRobie, Chris ; and Schoell, Ryan ; and Kaspar, Tiffany ; and Schreiber, Daniel ; and Kaoumi, Djamel}, year={2021}, month={Aug} } @article{agarwal_liedke_jones_reed_kohnert_uberuaga_wang_cooper_kaoumi_li_et al._2020, title={A new mechanism for void-cascade interaction from nondestructive depth-resolved atomic-scale measurements of ion irradiation-induced defects in Fe}, volume={6}, ISSN={["2375-2548"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85090069111&partnerID=MN8TOARS}, DOI={10.1126/sciadv.aba8437}, abstractNote={Positron annihilation spectroscopy and transmission electron microscopy yield previously unknown insights on radiation damage.}, number={31}, journal={SCIENCE ADVANCES}, author={Agarwal, S. and Liedke, M. O. and Jones, A. C. L. and Reed, E. and Kohnert, A. A. and Uberuaga, B. P. and Wang, Y. Q. and Cooper, J. and Kaoumi, D. and Li, N. and et al.}, year={2020}, month={Jul} } @article{derby_cooper_lach_martinez_kim_baldwin_kaoumi_edwards_schreiber_uberuaga_et al._2020, title={A pathway to synthesizing single-crystal Fe and FeCr films}, volume={403}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85091261473&partnerID=MN8TOARS}, DOI={10.1016/j.surfcoat.2020.126346}, abstractNote={Nuclear reactor environments provide a unique scientific and engineering challenge wherein materials must tolerate prolonged exposure to concurrent irradiation, elevated temperatures, and corrosive media. However, uncontrolled variability in material composition and structure often prohibits truly single-variable experiments that can reveal basic aspects of environmental damage. Magnetron sputtering is used here to provide a more controlled model system for these fundamental studies, yielding reproducible single-crystal Fe and FeCr thin films containing 8 and 18 at.% Cr. Electron microscopy is used to determine the systematic correlations between growth conditions and the resulting film microstructure and surface morphology. It is found that the substrate temperature and applied radio frequency (RF) bias can be tuned to obtain consistent homogeneous and single crystal films with a minimal amount of Ar impurities from the RF bias process. Epitaxial, single-crystal Fe films are obtained on MgO substrates at 500 °C with 10 Watt (W) RF bias deposition. However, when Cr is alloyed with Fe, higher substrate temperatures (600 °C) and applied RF biases (15 W) are required to achieve a similar epitaxial single-crystal FeCr film. Accelerated molecular dynamics simulations reveal that Cr impedes surface transport, explaining the need for higher temperature and bias during the growth of the Cr-bearing films.}, journal={Surface and Coatings Technology}, author={Derby, B. and Cooper, J. and Lach, T. and Martinez, E. and Kim, H. and Baldwin, J.K. and Kaoumi, D. and Edwards, D.J. and Schreiber, D.K. and Uberuaga, B.P. and et al.}, year={2020} } @article{fang_li_wang_ruiz_ma_wang_zhu_schoell_zheng_kaoumi_et al._2020, title={Achieving High Hetero-Deformation Induced (HDI) Strengthening and Hardening in Brass by Dual Heterostructures}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85109976273&partnerID=MN8TOARS}, DOI={10.2139/ssrn.3603553}, abstractNote={Abstract Heterostructured materials have a superior combination of strength and ductility, due to their ability to produce hetero-deform induced (HDI) strengthening and hardening. Therefore, achieving high HDI strengthening and hardening is the primary goal for designing heterostructures. Here we report a dual heterostructure in brass that consists of the heterogeneous lamella and gradient structure, fabricated by rolling, partial annealing, and rotationally accelerated shot peening (RASP). The dual heterostructures are able to generate extra interfaces of heterogeneity compared to the single heterostructures, which could lead to higher HDI strengthening and hardening, and a more superior combination of strength and ductility. This finding presents a new pathway to designing heterostructures in metallic materials.}, journal={SSRN}, author={Fang, X.T. and Li, Z.K. and Wang, Y.F. and Ruiz, M. and Ma, X.L. and Wang, H.Y. and Zhu, Y. and Schoell, R. and Zheng, C. and Kaoumi, D. and et al.}, year={2020} } @article{qiu_macdonald_li_schoell_kaoumi_hosemann_2020, title={An Electrochemical Impedance Spectroscopic Study of Oxide Films in Liquid Metal}, volume={72}, ISSN={["1543-1851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85082664384&partnerID=MN8TOARS}, DOI={10.1007/s11837-020-04120-9}, number={5}, journal={JOM}, author={Qiu, Jie and Macdonald, Digby D. and Li, Nan and Schoell, Ryan and Kaoumi, Djamel and Hosemann, Peter}, year={2020}, month={May}, pages={2082–2088} } @article{zheng_kaoumi_2020, title={Dislocation loop evolution in F/M steel T91 under in-situ ion irradiation: Influence of the presence of initial dislocations}, volume={540}, ISSN={["1873-4820"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85087763078&partnerID=MN8TOARS}, DOI={10.1016/j.jnucmat.2020.152363}, abstractNote={Ferritic/Martensitic (F/M) steel T91 was irradiated in-situ to 4 and 10 dpa at 470 °C using 1 MeV Kr2+. The microstructure evolution under irradiation was followed and characterized by in-situ Transmission Electron Microscopy (TEM), in terms of dislocation loop Burgers vector, average size and density as a function of dose. Furthermore, the influence of the presence of dislocations in the pre-irradiated matrix was investigated by comparing the radiation induced defect evolution in grains with and without initial dislocations.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Zheng, Ce and Kaoumi, Djamel}, year={2020}, month={Nov} } @article{fang_he_zheng_ma_kaoumi_li_zhu_2020, title={Effect of heterostructure and hetero-deformation induced hardening on the strength and ductility of brass}, volume={186}, ISSN={["1873-2453"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85078444623&partnerID=MN8TOARS}, DOI={10.1016/j.actamat.2020.01.037}, abstractNote={Heterostructured materials have been reported to possess superior combinations of strength and ductility, which is attributed to hetero-deformation induced (HDI) strengthening and work hardening. However, the influence of heterostructural parameters on the evolution of HDI stress and mechanical behavior during tensile deformation is not well understood. In this paper, heterostructured brass (Cu–30%Zn) was fabricated by cold rolling and partial annealing, to produce heterostructures with different heterostructural parameters, including domain volume fraction, domain thickness/spacing and domain misorientation. It was found that HDI hardening was dominant when the tensile strain was less than ∼4.5%, while conventional dislocation hardening became more effective at higher strain levels. Quick accumulation of geometrically necessary dislocations was found in the domain boundary regions, leading to high HDI stress. Higher domain misorientation was found more effective in developing HDI hardening. These findings elucidate the effect of heterostructure on strength and ductility, which can help with the design of heterostructured materials for superior mechanical properties.}, journal={ACTA MATERIALIA}, publisher={Elsevier BV}, author={Fang, X. T. and He, G. Z. and Zheng, C. and Ma, X. L. and Kaoumi, D. and Li, Y. S. and Zhu, Y. T.}, year={2020}, month={Mar}, pages={644–655} } @article{qiu_han_schoell_popovic_ghanbari_kaoumi_scully_macdonald_hosemann_2020, title={Electrical properties of thermal oxide scales on pure iron in liquid lead-bismuth eutectic}, volume={176}, ISSN={["1879-0496"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85092125613&partnerID=MN8TOARS}, DOI={10.1016/j.corsci.2020.109052}, abstractNote={The impedance behavior of pre-oxidized iron in liquid lead-bismuth eutectic (LBE) at 200 °C is studied using electrochemical impedance spectroscopy. The structures and resistance of oxide grown on iron oxidized in air at different temperatures and durations are compared. The results show that the resistance of the oxide film increases with increasing oxidizing temperature, due to the formation of a thicker scale and fewer defects. At the same temperature (600 °C), increasing the oxidation time can also reduce the defect concentration in the oxide film and improve the impedance of the oxide scale in LBE.}, journal={CORROSION SCIENCE}, author={Qiu, Jie and Han, Junsoo and Schoell, Ryan and Popovic, Miroslav and Ghanbari, Elmira and Kaoumi, Djamel and Scully, John R. and Macdonald, Digby D. and Hosemann, Peter}, year={2020}, month={Nov} } @article{qiu_han_schoell_popovic_ghanbari_kaoumi_scully_macdonald_hosemann_2020, title={Electrical properties of thermal oxide scales on pure iron in liquid lead-bismuth eutectic}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85169498933&partnerID=MN8TOARS}, DOI={10.48550/arxiv.2010.05372}, abstractNote={The impedance behavior of pre-oxidized iron in liquid lead-bismuth eutectic (LBE) at 200 oC is studied using electrochemical impedance spectroscopy. The structures and resistance of oxide grown on iron oxidized in air at different temperatures and durations are compared. The results show that the resistance of the oxide film increases with increasing oxidizing temperature, due to the formation of a thicker scale and fewer defects. At the same temperature (600 oC), increasing the oxidation time can also reduce the defect concentration in the oxide film and improve the impedance of the oxide scale in LBE.}, journal={arXiv}, author={Qiu, J. and Han, J. and Schoell, R. and Popovic, M. and Ghanbari, E. and Kaoumi, D. and Scully, J.R. and Macdonald, D.D. and Hosemann, P.}, year={2020} } @article{duemmler_zheng_baumier_gentils_kaoumi_2021, title={Helium bubble nucleation and growth in alloy HT9 through the use of in situ TEM: Sequential he-implantation and heavy-ion irradiation versus dual-beam irradiation}, volume={545}, ISSN={["1873-4820"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85095569165&partnerID=MN8TOARS}, DOI={10.1016/j.jnucmat.2020.152641}, abstractNote={The formation of He bubbles in Ferritic/Martensitic steel HT9 is investigated through the use of in situ Transmission Electron Microscopy coupled with He implantation and heavy ion irradiation. Of particular interest is the effect of increasing He appm/dpa ratio on the formation and growth of the bubbles, as well as the effect of the sequential order of ion irradiation i.e. He-pre-implantation followed by heavy-ion irradiation versus true dual-beam irradiation. The role of He is discussed.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Duemmler, Kai and Zheng, Ce and Baumier, Cedric and Gentils, Aurelie and Kaoumi, Djamel}, year={2021}, month={Mar} } @article{schoell_frazer_zheng_hosemann_kaoumi_2020, title={In Situ Micropillar Compression Tests of 304 Stainless Steels After Ion Irradiation and Helium Implantation}, volume={72}, ISSN={["1543-1851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85082954591&partnerID=MN8TOARS}, DOI={10.1007/s11837-020-04127-2}, number={7}, journal={JOM}, author={Schoell, Ryan and Frazer, David and Zheng, Ce and Hosemann, Peter and Kaoumi, Djamel}, year={2020}, month={Jul}, pages={2778–2785} } @article{owusu-mensah_cooper_kaoumi_2020, title={In situ TEM investigation of irradiation induced amorphization of fe oxide}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85094840050&partnerID=MN8TOARS}, DOI={10.1017/S1431927620016189}, abstractNote={Even though significant progress has been made in the past decades, there is still a lot of essential information that could contribute to a better understanding of material properties in extreme conditions. One typical area of limited information is the effect of radiation damage in oxides and the interfaces between metals and oxides. In fact, there is significant amount of research and data related to irradiation damage in steels but literature is scarce for radiation damage in oxides. Oxides grow at metal surfaces under the corrosive environment of nuclear reactors. Understanding the irradiation induced defect formation and their mobility in the oxides and across interfaces could provide valuable information in predicting the behavior of these materials at extreme conditions. There is reasonable information available in literature pertaining to the radiation damage in oxides with the fluoride[1], pyrochlore[1,2] or spinel crystal structures[3]. Surprisingly, there is very little information on the irradiation damage in various forms of oxides of iron and chromium systems even though these oxides remain the most common oxide formation in steels and thus in steel components in a reactor.}, journal={Microscopy and Microanalysis}, author={Owusu-Mensah, M. and Cooper, J. and Kaoumi, D.}, year={2020} } @article{schoell_xi_zhao_wu_yu_kenesei_almer_shayer_kaoumi_2020, title={In situ synchrotron X-ray tomography of 304 stainless steels undergoing chlorine-induced stress corrosion cracking}, volume={170}, ISSN={["1879-0496"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85083895132&partnerID=MN8TOARS}, DOI={10.1016/j.corsci.2020.108687}, abstractNote={To understand the mechanisms behind chlorine-induced stress corrosion cracking (CISCC) in 304 stainless steel, synchrotron high energy x-rays were used to perform in-situ x-ray microtomography on a pre-cracked sample under load in a corrosive simulated marine environment. The tomography scans showed the crack morphology evolving into a branching crack around the surface of the sample. Finite element analysis and stress intensity analysis are conducted to explain the observed crack branching.}, journal={CORROSION SCIENCE}, author={Schoell, Ryan and Xi, Li and Zhao, Yuchen and Wu, Xin and Yu, Zhenzhen and Kenesei, Peter and Almer, Jonathan and Shayer, Zeev and Kaoumi, Djamel}, year={2020}, month={Jul} } @article{zhao_cinbiz_park_almer_kaoumi_2020, title={Tensile behavior and microstructural evolution of a Fe-25Ni-20Cr austenitic stainless steel (alloy 709) from room to elevated temperatures through in-situ synchrotron X-ray diffraction characterization and transmission electron microscopy}, volume={540}, ISSN={["1873-4820"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85088120696&partnerID=MN8TOARS}, DOI={10.1016/j.jnucmat.2020.152367}, abstractNote={Uniaxial tensile tests were done on Fe-25Ni-20Cr Austenitic Stainless Steel (Alloy 709) along with in-situ synchrotron measurement at different temperatures (25 °C, 500 °C, 700 °C and 900 °C). The X-Ray diffraction data was collected in-situ in order to follow the phases present as well as to derive the dislocation density as a function of strain through peak broadening analysis based on the modified Williamson-Hall method and see how trends are affected as a function of temperature. The XRD data were complemented by TEM and STEM-EDX characterization done on the post-experiment samples to observe the deformed microstructures. The paper presents a depiction of the tensile behavior of this advanced steel by interpreting the stress-strain curves and the effect of temperature through the information gained by in-situ XRD and TEM observations as well as fractography done ex-situ on the samples tested to rupture.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Zhao, Yuchen and Cinbiz, Mahmut N. and Park, Jun-Sang and Almer, Jonathan and Kaoumi, Djamel}, year={2020}, month={Nov} } @article{remillieux_kaoumi_ohara_geesey_xi_schoell_bryan_enos_summa_ulrich_et al._2020, title={Detecting and imaging stress corrosion cracking in stainless steel, with application to inspecting storage canisters for spent nuclear fuel}, volume={109}, ISSN={["1879-1174"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85074748303&partnerID=MN8TOARS}, DOI={10.1016/j.ndteint.2019.102180}, abstractNote={One of the primary concerns with the long-term performance of storage systems for spent nuclear fuel (SNF) is the potential for corrosion due to deliquescence of salts deposited as aerosols on the surface of the canister, which is typically made of austentic stainless steel. In regions of high residual weld stresses, this may lead to localized stress-corrosion cracking (SCC). The ability to detect and image SCC at an early stage (long before the cracks are susceptible to propagate through the thickness of the canister wall and leaks of radioactive material may occur) is essential to the performance evaluation and licensing process of the storage systems. In this paper, we explore a number of nondestructive testing techniques to detect and image SCC in austenitic stainless steel. Our attention is focused on a small rectangular sample of 1 × 2 in2 with two cracks of mm-scale sizes. The techniques explored in this paper include nonlinear resonant ultrasound spectroscopy (NRUS) for detection, Linear Elastodynamic Gradient Imaging Technique (LEGIT), ultrasonic C-scan, vibrothermography, and synchrotron X-ray diffraction for imaging. Results obtained from these techniques are compared. Cracks of mm-scale sizes can be detected and imaged with all the techniques explored in this study.}, journal={NDT & E INTERNATIONAL}, author={Remillieux, Marcel C. and Kaoumi, Djamel and Ohara, Yoshikazu and Geesey, Marcie A. Stuber and Xi, Li and Schoell, Ryan and Bryan, Charles R. and Enos, David G. and Summa, Deborah A. and Ulrich, T. J. and et al.}, year={2020}, month={Jan} } @article{marsh_schoell_kaoumi_2019, title={Environmental effect on mechanical properties of a gamma-prime strengthened nickel-based alloy: Effect of the surface oxidation and formation of gamma-prime free zones}, volume={752}, ISSN={["1873-4936"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85062646666&partnerID=MN8TOARS}, DOI={10.1016/j.msea.2019.03.013}, abstractNote={The mechanical behavior of X-750 in rough vacuum environment was explored and compared with the mechanical behavior in air at a large range of temperatures (from room temperature to 900°C) for both Heat-Treated and Non-Heat-Treated X750 alloy. In the intermediate range of temperatures where the Portevin Le Chatelier (PLC) effect is observed, the effect of testing in air versus rough vacuum did not yield statistically significant different PLC characteristics. At temperatures above 650°C for Heat Treated and 750°C for Non-Heat-Treated X-750, the samples tested under rough vacuum had higher yield stress values than the respective samples tested under air. The decrease in yield stress under air was attributed to an oxide scale induced surface softening effect and the loss of strengthening efficiency for the gamma prime precipitates. At higher temperatures in air, around 800°-900°C, sinusoidal stress serrations in the stress strain curves indicated the occurrence of dynamic recrystallization (DRX). The vacuum environment however removed all stress serrations attributed to DRX, indicating that the surface oxidation with the concomitant formation of a γ' free zone underneath the oxide layer plays a role in the DRX presence.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Marsh, Christopher and Schoell, Ryan and Kaoumi, Djamel}, year={2019}, month={Apr}, pages={136–144} } @article{kaoumi_jammot_2019, title={Insights into the plastic behavior of irradiated Ni-based alloy through in-situ TEM experiments: Formation and evolution of defect-free channels}, volume={523}, ISSN={["1873-4820"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85066288070&partnerID=MN8TOARS}, DOI={10.1016/j.jnucmat.2019.05.037}, abstractNote={Foils of Ni-based alloys are deformed in situ in a TEM at 298 K after irradiation at the same temperature to 1014 ions/cm2 with 1 MeV Kr ions. The irradiation effects on the dislocation sources, dislocation motion, and on dislocation interactions with each other and the microstructure are assessed through in-situ dynamic observations. Dislocation motion through the irradiated material is observed to be jerky and discontinuous, as they get pinned by the irradiation-induced defects and the progression of the pile-ups proceeds in bursts of multiple dislocations. Active sources of dislocations originating from the walls of the channels are captured in-situ. They provide dislocations that glide in the channel and progressively clear it of the defects. Dislocation interactions with irradiation defects result in their increase in length by absorption of the defects; dislocations can become longer than the width of the channel, which can lead to congested channels and heavily jogged dislocations, resulting in a higher driving force for dislocation cross-slip out of the channels into the outside matrix, a phenomenon also captured in-situ. Similar observations were done in both Inconel 617 and Haynes 230, a similar Ni-based alloy with different composition but similar Stacking Fault Energy, indicating that the mechanisms at play are not strongly dependent on the chemical composition.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Kaoumi, D. and Jammot, V}, year={2019}, month={Sep}, pages={33–42} } @inproceedings{kabel_koyanagi_katoh_schoell_kaoumi_ang_hosemann_2019, title={Interface characterization of candidate dual-purpose barrier coatings for SiC/SiC accident tolerant fuel cladding}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85080034549&partnerID=MN8TOARS}, booktitle={19th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, EnvDeg 2019}, author={Kabel, J. and Koyanagi, T. and Katoh, Y. and Schoell, R. and Kaoumi, D. and Ang, C. and Hosemann, P.}, year={2019}, pages={1043–1051} } @misc{barr_el-atwani_kaoumi_hattar_2019, title={Interplay Between Grain Boundaries and Radiation Damage}, volume={71}, ISSN={["1543-1851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85062726933&partnerID=MN8TOARS}, DOI={10.1007/s11837-019-03386-y}, number={4}, journal={JOM}, author={Barr, Christopher M. and El-Atwani, Osman and Kaoumi, Djamel and Hattar, Khalid}, year={2019}, month={Apr}, pages={1233–1244} } @article{zheng_reese_field_liu_marquis_maloy_kaoumi_2020, title={Microstructure response of ferritic/martensitic steel HT9 after neutron irradiation: Effect of temperature}, volume={528}, ISSN={["1873-4820"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85073823752&partnerID=MN8TOARS}, DOI={10.1016/j.jnucmat.2019.151845}, abstractNote={The ferritic/martensitic steel HT9 was irradiated in the BOR-60 reactor at 650, 690 and 730 K (377, 417 and 457 °C) to doses between ∼14.6–18.6 displacements per atom (dpa). Irradiated samples were comprehensively characterized using analytical scanning/transmission electron microscopy and atom probe tomography, with emphasis on the influence of irradiation temperature on microstructure evolution. Mn/Ni/Si-rich (G-phase) and Cr-rich (αʹ) precipitates were observed within martensitic laths and at various defect sinks at 650 and 690 K (377 and 417 °C). For both G-phase and αʹ precipitates, the number density decreased while the size increased with increasing temperature. At 730 K (457 °C), within martensitic laths, a very low density of large G-phase precipitates nucleating presumably on dislocation lines was observed. No αʹ precipitates were observed at this temperature. Both a <100> and a/2 <111> type dislocation loops were observed, with the a <100> type being the predominant type at 650 and 690 K (377 and 417 °C). On the contrary, very few dislocation loops were observed at 730 K (457 °C), and the microstructure was dominated by a/2 <111> type dislocation lines (i.e., dislocation network) at this temperature. Small cavities (diameter < 2 nm) were observed at all three temperatures, whereas large cavities (diameter > 2 nm) were observed only at 690 K (417 °C), resulting in a bimodal cavity size distribution at 690 K (417 °C) and a unimodal size distribution at 650 and 730 K (377 and 457 °C). The highest swelling (%) was observed at 690 K (417 °C), indicating that the peak of swelling happens between 650 and 730 K (377 and 457 °C).}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Zheng, Ce and Reese, Elaina R. and Field, Kevin G. and Liu, Tian and Marquis, Emmanuelle A. and Maloy, Stuart A. and Kaoumi, Djamel}, year={2020}, month={Jan} } @article{zheng_reese_field_marquis_maloy_kaoumi_2019, title={Microstructure response of ferritic/martensitic steel HT9 after neutron irradiation: effect of dose}, volume={523}, ISSN={["1873-4820"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85067602813&partnerID=MN8TOARS}, DOI={10.1016/j.jnucmat.2019.06.019}, abstractNote={A ferritic/martensitic steel, HT9, was irradiated in the BOR-60 reactor to ∼17.1 and ∼35.1 displacements per atom (dpa) at 650 ± 23 K (377 ± 23 °C). Irradiated samples were comprehensively characterized using analytical scanning/transmission electron microscopy and atom probe tomography, with emphasis on the role of irradiation dose on the microstructure evolution. Radiation-induced Mn/Ni/Si-rich (G-phase) and radiation-enhanced Cr-rich (αʹ) precipitates were observed within the martensitic laths at all doses. In addition, the G-phase was also observed to precipitate heterogeneously at various defect sinks. The number density for these second-phase precipitates decreases while the size increases with increasing dose, resulting in an increase of the volume fraction. Both a <100> and a/2 <111> type loops were observed with the a <100> type being the predominant type at both doses. The proportion of a <100> loops is consistent with that previously observed in HT9 ion irradiated to similar doses at ∼693–743 K (∼420-470 °C). Only small cavities (diameter < 2 nm) were observed at ∼17.1 dpa whereas both small and large cavities were observed at ∼35.1 dpa, resulting in a bi-modal cavity size distribution at this dose. Alloying elements, Ni and Si, were observed to segregate to the cavity surface, forming Ni/Si-rich shells around the cavities. The swelling at ∼17.1 dpa is evaluated at ∼0.02% while the swelling at ∼35.1 dpa is found to be ∼0.07% with variations from grain to grain. attributed to the spatial variation of the density of large cavities (in different grains). The swelling data obtained in this study was compared with the neutron data of F/M steels available in the literature.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Zheng, Ce and Reese, Elaina R. and Field, Kevin G. and Marquis, Emmanuelle and Maloy, Stuart A. and Kaoumi, Djamel}, year={2019}, month={Sep}, pages={421–433} } @article{zheng_ke_maloy_kaoumi_2019, title={Correlation of in-situ transmission electron microscopy and microchemistry analysis of radiation-induced precipitation and segregation in ion irradiated advanced ferritic/martensitic steels}, volume={162}, ISSN={["1359-6462"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85058704067&partnerID=MN8TOARS}, DOI={10.1016/j.scriptamat.2018.12.018}, abstractNote={This article presents a novel method combining ion irradiation, in-situ transmission electron microscopy (TEM), and microchemistry analysis before/after irradiation, which allows to examine same microstructural areas throughout ion irradiation. A 12 wt% Cr Ferritic/Martensitic steel (HT9) was irradiated in the TEM to 1.17 × 1020 ions·m−2 at 440 °C using 1 MeV Kr2+ ions, and the in-situ characterization focused on radiation-induced precipitation and segregation. Results of in-situ experiments were compared with those obtained from ex-situ experiments, to showcase how this method helps to better understand precipitation kinetics in the irradiated material examined ex-situ, for which only snapshots are available at limited doses.}, journal={SCRIPTA MATERIALIA}, author={Zheng, Ce and Ke, Jia-Hong and Maloy, Stuart A. and Kaoumi, Djamel}, year={2019}, month={Mar}, pages={460–464} } @article{zheng_maloy_kaoumi_2018, title={Effect of dose on irradiation-induced loop density and Burgers vector in ion-irradiated ferritic/martensitic steel HT9}, volume={98}, ISSN={1478-6435 1478-6443}, url={http://dx.doi.org/10.1080/14786435.2018.1490825}, DOI={10.1080/14786435.2018.1490825}, abstractNote={ABSTRACT Samples of F/M steel HT9 were irradiated to 20 dpa at 420°C, 440°C and 470°C in a transmission electron microscope with 1 MeV Kr ions so that the microstructure evolution could be followed in situ and characterised as a function of dose. Dynamic observations of irradiation-induced defect formation and evolution were made at the different temperatures. Irradiation-induced loops were characterised in terms of their Burgers vector, size and density as a function of dose and similar observations and trends were found at the three temperatures: (i) both a/2 <111> and a <100> loops are observed; (ii) in the early stage of irradiation, the density of irradiation-induced loops increases with dose (0–4 dpa) and then decreases at higher doses (above 4 dpa), (iii) the dislocation line density shows an inverse trend to the loop density with increasing dose: in the early stages of irradiation, the pre-existing dislocation lines are lost by climb to the surfaces while at higher doses (above 4 dpa), the build-up of new dislocation networks is observed along with the loss of the radiation-induced dislocation loops to dislocation networks; (iv) at higher doses, the decrease of number of loops affects more the a/2 <111> loop population; the possible loss mechanisms of the a/2 <111> loops are discussed. Also, the ratio of a <100> to a/2 <111> loops is found to be similar to cases of bulk irradiation of the same alloy using 5 MeV Fe2+ ions to similar doses of 20 dpa at similar temperatures.}, number={26}, journal={Philosophical Magazine}, publisher={Informa UK Limited}, author={Zheng, Ce and Maloy, Stuart and Kaoumi, Djamel}, year={2018}, month={Jul}, pages={2440–2456} } @book{shayer_yu_olson_liu_gordon_wu_murty_kumar_kaoumi_anderson_et al._2018, title={Integrated research program overview on the “innovative approaches to marine atmospheric stress corrosion cracking inspection, evaluation and modeling in used-fuel dry storage canisters”}, volume={262}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85055490485&partnerID=MN8TOARS}, journal={Ceramic Transactions}, author={Shayer, Z. and Yu, Z. and Olson, D.L. and Liu, S. and Gordon, S. and Wu, X. and Murty, K.L. and Kumar, N. and Kaoumi, D. and Anderson, B. and et al.}, year={2018}, pages={151–164} } @article{zheng_schoell_hosemann_kaoumi_2019, title={Ion irradiation effects on commercial PH 13-8 Mo maraging steel Corrax}, volume={514}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85058006280&partnerID=MN8TOARS}, DOI={10.1016/j.jnucmat.2018.11.041}, abstractNote={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 β-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.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Zheng, Ce and Schoell, Ryan and Hosemann, Peter and Kaoumi, Djamel}, year={2019}, pages={255–265} } @article{kaoumi_liu_2018, title={Deformation induced martensitic transformation in 304 austenitic stainless 1 steel: In-situ vs. ex-situ transmission electron microscopy characterization}, volume={715}, ISSN={["1873-4936"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85039942481&partnerID=MN8TOARS}, DOI={10.1016/j.msea.2017.12.036}, abstractNote={304 stainless steel is known to be metastable as the austenite phase can transform into martensite under deformation. In this work, both ex-situ and in-situ transmission electron microscopy (TEM) characterization were used to investigate the mechanisms of the deformation-induced transformation at room temperature. The ex-situ tensile tests were conducted at a strain rate of 10−3 s−1 until rupture, followed by TEM and X-Ray Diffraction (XRD). Samples were also interrupted at strains of 7%, 18%, and 30% with the goal of investigating the intermediate microstructure. In addition, tensile tests were conducted in-situ in a TEM at 25 °C using a special straining-stage with the goal of capturing the nucleation and growth of the martensitic phase as it develops under deformation. The formation of stacking faults and the subsequent formation of ε-martensite (hcp) through their overlapping/bundling was captured in-situ, confirming the role played by Stacking Faults (SFs) as intermediate step during the transformation from γ-austenite to ε-martensite. Direct transformation of γ-austenite (fcc) to α’-martensite (bcc) was also captured upon straining and characterized. Such unique in-situ observations showcase how in-situ straining in a TEM, as a small scale tensile technique, is a powerful technique to visualize and investigate the mechanisms of deformation induced phase transformations.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Kaoumi, Djamel and Liu, Junliang}, year={2018}, month={Feb}, pages={73–82} } @article{hosemann_frazer_kaoumi_zheng_2017, title={Microstructural and Nanomechanical Characterization of In-Situ He Implanted and Irradiated fcc Materials}, volume={23}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/S1431927617004445}, DOI={10.1017/S1431927617004445}, abstractNote={Nuclear Materials research focusing on the degradation of materials utilized in nuclear environments has been studied for decades. This research aims to assess the microstructural changes and therefore mechanical property degradation as a function of radiation dose at representative temperatures and environments. Traditionally specimens are exposed to reactor or ion beam irradiation and subsequently examined using transmission electron microscopy, atom probe tomography, X-ray techniques and mechanical testing. However, all these techniques are mostly conducted ex-situ and one only observes the resulting changes but not on the same sample or same location making interpretations sometimes challenging. Following the defect development has been achieved utilizing tools like the Intermediate Voltage Electron Microscopy (IVEM) facility or other similar in-situ irradiation facilities [1]. Modern He ion beam microscopes also allow direct implantation of He in samples on a very localized level allowing localized He implantation on specific regions of interest on the same TEM foil [2]. While these are a very useful tools the damage evolution has only been followed on TEM foils and no mechanical data has been extracted from the irradiated samples. Ideally one would be able to extract a change in mechanical property associated with the microstructural changes. Recent advantages in nanomechanical testing and in-situ ion beam irradiation have the potential to obtain both microstructural data as well as mechanical property data on the same sample. This work attempts to perform the entire study in-situ spanning from He implantation to displacement damage and subsequent mechanical property evaluation to follow the defect development from the beginning to its implications for mechanical properties. It is anticipated that this procedure developed here will allow to establish a process producing data for model benchmarking bridging the gap between modeling and experiments on the same length-scale.}, number={S1}, journal={Microscopy and Microanalysis}, publisher={Cambridge University Press (CUP)}, author={Hosemann, P. and Frazer, D. and Kaoumi, D. and Zheng, C.}, year={2017}, month={Jul}, pages={756–757} } @article{byun_kaoumi_bai_2017, title={Microstructural processes in irradiated materials}, volume={497}, ISSN={["1873-4820"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85034065974&partnerID=MN8TOARS}, DOI={10.1016/j.jnucmat.2017.10.065}, abstractNote={Irradiation conditions such as fission power, fission rates, and temperature are important parameters for nuclear fuels because they influence the microstructural behavior and ultimate irradiation performance. Two U-7Mo/Al-3.5 wt.% Si dispersion fuel plates were irradiated in the Advanced Test Reactor edge-on to the core in the RERTR-9B experiment at different powers to study the effects of power on fuel phase swelling behavior. The results of non-destructive measurements have been reported in a previous paper [1], and the destructive examination results are being reported here. In particular, the microstructural evolution of the U-Mo fuel phase in irradiated fuel plates has been investigated by cutting transverse cross-sections, using generated scanning electron microscopy micrographs, and image processing methods to assess the changes in microstructural features, such as fission gas pore growth and non-recrystallized grain fraction. In this study, the focus was to examine the evolution of fission gas pores from both the constrained and unconstrained regions of U-Mo fuels irradiated at different powers. Based on an estimated linear gradient, the rate of change of fission gas pore size with locally calculated fission densities is more prominent in the higher power specimen. As such, the average porosity and pore area is approximately 11% and 2 × larger in the fuel irradiated at higher power than that of the lower power specimen. The growth of fission gas pores can accelerate the pore interconnectivity and thus fission gas outside the fuel kernel (FGO), which are two precursors for swelling in U-Mo fuels. The influence of increased power, internal plate stresses, and fission-induced creep on fuel kernel deformation and lateral mass transfer is also highlighted.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Byun, Thak Sang and Kaoumi, Djamel and Bai, Xian-Ming}, year={2017}, month={Dec}, pages={107–107} } @article{kaoumi_zheng_2017, title={Microstructure Characterization of Ion-irradiated Ferritic/Martensitic HT9 Steel}, volume={23}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/S1431927617011734}, DOI={10.1017/S1431927617011734}, abstractNote={HT9 is a 12Cr Ferritic/Martensitic (F/M) steel considered as a promising candidate for structural and cladding applications in Generation IV reactors [1]. The chemical composition of the alloy is given in Table 1. The harsh service conditions in Gen IV reactors require that the microstructural response to irradiation of the candidate structural alloys be investigated and understood to qualify them. For that matter, a series of ion irradiations were done. Bulk HT9 specimens were irradiated using 5 MeV Fe ions to 20 displacements per atom (dpa) at 600 nm depth with a dose rate approximately to 5×10 dpa/s, at irradiation temperatures of 420, 440 and 470°C (with a variation of ± 5°C). The temperature was monitored using an infrared camera and four attached Type J thermocouples. For post-irradiation characterization, TEM specimens were firstly prepared by the FIB lift-out method using a FEI Quanta focused ion beam (FIB) instrument. ChemiSTEM characterizations were then conducted on FIB laminas using a FEI Titan 80-300 probe aberration corrected microscope. ChemiSTEM characterization was also conducted on as-received HT9 prior to ion irradiation. Only pre-existed M23C6 type carbides and V-rich nitride precipitates were observed in the as-received condition. In contrast, Ni-Si-Mn rich precipitates (also known as G phase) were found in HT9 irradiated to 20 dpa at 420, 440 and 470°C, as shown in Figure 1. Radiation-induced Ni segregation was also observed at grain boundaries, which is highlighted by white arrows in Figure 2. In addition, the G phase precipitates were found to nucleate heterogeneously along lath grain boundaries, as indexed by red arrows in Figure 2. The observed results indicated that, under self-ion irradiation, alloying elements such as Ni, Si and Mn segregate at defect sinks, which become thus favourable nucleation sites and promote the radiation-induced G phase precipitation. While radiation induced precipitation and segregation in neutron irradiated F/M HT9 have been widely reported in the literature, similar investigations under ion irradiation have been more scarce [2,3,4]. In fact, this study serves to generate baseline data on ion irradiation effects on F/M HT9 in an effort to learn how to more accurately choose ion-irradiation experimental conditions to emulate the irradiated microstructures and effects observed under neutron irradiation. Ion irradiations were also carried out in the same alloy at similar temperatures in-situ in a TEM using 1MeV Kr++ ions so that the microstructure characterized in-situ in the TEM can be compared with the microstructure achieved on the same alloys using self-ion irradiation on bulk samples. The focus of the comparison is put on the size and density of dislocation loops induced by irradiation, as well as dislocation loop burgers vector determination. The in-situ experiments provide data on the kinetics of irradiation induced defect formation and evolution, and on the damage spatial correlation with the preexisting microstructure, and thus can help understand how the microstructures observed ex-situ in the bulk samples have developed for, in these latter cases, only snapshots are available at the limited doses. By comparing the ex-situ and in-situ irradiation it is also possible to substantiate the free surface effect on the radiation induced microstructure. The presentation will also report such comparison.}, number={S1}, journal={Microscopy and Microanalysis}, publisher={Cambridge University Press (CUP)}, author={Kaoumi, Djamel and Zheng, Ce}, year={2017}, month={Jul}, pages={2214–2215} } @article{zheng_auger_moody_kaoumi_2017, title={Radiation induced segregation and precipitation behavior in self-ion irradiated Ferritic/Martensitic HT9 steel}, volume={491}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85019131192&partnerID=MN8TOARS}, DOI={10.1016/j.jnucmat.2017.04.040}, abstractNote={In this study, Ferritic/Martensitic (F/M) HT9 steel was irradiated to 20 displacements per atom (dpa) at 600 nm depth at 420 and 440 °C, and to 1, 10 and 20 dpa at 600 nm depth at 470 °C using 5 MeV Fe++ ions. The characterization was conducted using ChemiSTEM and Atom Probe Tomography (APT), with a focus on radiation induced segregation and precipitation. Ni and/or Si segregation at defect sinks (grain boundaries, dislocation lines, carbide/matrix interfaces) together with Ni, Si, Mn rich G-phase precipitation were observed in self-ion irradiated HT9 except in very low dose case (1 dpa at 470 °C). Some G-phase precipitates were found to nucleate heterogeneously at defect sinks where Ni and/or Si segregated. In contrast to what was previously reported in the literature for neutron irradiated HT9, no Cr-rich α′ phase, χ-phases, η phase and voids were found in self-ion irradiated HT9. The difference of observed microstructures is probably due to the difference of irradiation dose rate between ion irradiation and neutron irradiation. In addition, the average size and number density of G-phase precipitates were found to be sensitive to both irradiation temperature and dose. With the same irradiation dose, the average size of G-phase increased whereas the number density decreased with increasing irradiation temperature. Within the same irradiation temperature, the average size increased with increasing irradiation dose.}, journal={Journal of Nuclear Materials}, author={Zheng, C. and Auger, M. A. and Moody, M. P. and Kaoumi, Djamel}, year={2017}, pages={162–176} } @article{zheng_kaoumi_2017, title={Radiation-induced swelling and radiation-induced segregation & precipitation in dual beam irradiated Ferritic/Martensitic HT9 steel}, volume={134}, ISSN={["1873-4189"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85032004953&partnerID=MN8TOARS}, DOI={10.1016/j.matchar.2017.10.019}, abstractNote={Ferritic/Martensitic HT9 steel was irradiated at 432 °C to 16.6 displacements per atom (dpa) (at the depth of 600 nm) using a defocused beam of 5 MeV Fe++ ions, while co-implanted with 3.22 appm He at the same depth. The helium concentration profile was designed so to follow the damage curve with a 0.22 appm He/dpa ratio at the depth from 300 to 1000 nm in the material. The depth-dependence of the cavity size and number density were characterized by both transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) imaging methods. A comparison between the two techniques was done showing good agreement. Cavity number density and the resulting swelling were found to be suppressed by the injected interstitial effect in the vicinity of the ion induced damage peak. The region between 300 and 750 nm depth which excludes the injected interstitial effect was thus proposed for improved cavity swelling analysis. The swelling ratio in this region was found to be ~(0.86–1.02) × 10− 2%/dpa. In addition, ChemiSTEM characterization revealed radiation-induced segregation occurring throughout the irradiated region and precipitation of G-phase particles. Segregation of Ni to cavity surfaces was also observed and its possible synergistic influence on swelling was discussed.}, journal={MATERIALS CHARACTERIZATION}, author={Zheng, C. and Kaoumi, D.}, year={2017}, month={Dec}, pages={152–162} } @article{marsh_kaoumi_2017, title={Serrated tensile flow in inconel X750 sheets: Effect of heat treatment}, volume={707}, ISSN={["1873-4936"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85029407145&partnerID=MN8TOARS}, DOI={10.1016/j.msea.2017.08.093}, abstractNote={The tensile behavior of gamma prime precipitation hardened nickel-chromium superalloy X-750 sheets was investigated in the as received (i.e. non-heat treated NHT) and heat treated (HT) states. The evolution of mechanical properties were studied as a function of strain rate (10−3, 10−4, and 10−5 s−1) and temperature (23–900 °C). The Portevin Le Chatelier (PLC) effect was observed in both HT and NHT X-750, with the occurrence of saw-tooth type serrations accompanying hardening until rupture at intermediate temperatures. Above 800–900 °C, the stress-strain curves showed a softening effect, with the occurrence of sinusoidal serrations indicative of Dynamic Recristallization. The temperature ranges of the PLC effect were determined for both NHT and HT X750 highlighting the effect of heat treatment. The strain rate was observed to shift the PLC temperature regime for both NHT and HT X-750. Type A, B, and C PLC serrations were observed for both HT and NHT, and serration amplitude increased with temperature and decreasing strain rate. The NHT X-750 was found to exhibit more instances of normal PLC effect whereas the HT material exhibited more cases of inverse PLC behavior. The normal PLC regime activation energies were calculated for both NHT and HT cases respectively, and the results suggest carbon as the responsible solute for serrations in this range.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Marsh, C. and Kaoumi, D.}, year={2017}, month={Nov}, pages={136–147} } @article{liu_kaoumi_2018, title={Use of in-situ TEM to characterize the deformation-induced martensitic transformation in 304 stainless steel at cryogenic temperature}, volume={136}, ISSN={["1873-4189"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85039786189&partnerID=MN8TOARS}, DOI={10.1016/j.matchar.2017.12.005}, abstractNote={Tensile tests are conducted in-situ in a TEM at cryogenic temperatures (from − 100 °C to 0 °C) using a cooling TEM straining-stage with the goal of capturing the growth of the martensitic phase as it develops under stress in the material. The in-situ technique is used to explore the mechanism of deformation induced martensitic transformation in 304 and 304L austenitic stainless steels. The formation of stacking faults is captured, as well as the subsequent formation of ε-martensite, confirming the role played by Stacking faults (SFs) as intermediate step during the transformation from γ-austenite to ε-martensite. In addition, direct transformation from γ-austenite to α′-martensite is captured (i) upon straining at a fixed temperature and (ii) upon cooling after pulling on the sample, indicating how straining and temperature are both effective on the transformation.}, journal={MATERIALS CHARACTERIZATION}, author={Liu, J. and Kaoumi, D.}, year={2018}, month={Feb}, pages={331–336} } @article{marsh_depinoy_kaoumi_2016, title={Effect of heat treatment on the temperature dependence of the fracture behavior of X-750 alloy}, volume={677}, ISSN={["1873-4936"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84988689036&partnerID=MN8TOARS}, DOI={10.1016/j.msea.2016.09.081}, abstractNote={X-750 is a nickel-chromium based super alloy of usefulness in a wide variety of applications such as gas turbines, rocket engines, nuclear reactors, pressure vessels, tooling, and aircraft structures. Its good mechanical properties are due to the strengthening from precipitation of γ′ particles upon prior ageing heat treatment. In this work, the effect of such heat treatment on the fracture mechanisms of X-750 was studied at various temperatures by comparing it with a non-aged, solution annealed X-750. Tensile tests were conducted from room temperatures up to 900 °C; fracture surfaces were analyzed by means of SEM observations. In addition, the microstructure of both aged and solution annealed materials were studied using SEM and TEM, both on as received and on tested specimens. In terms of mechanical properties, as expected, the yield strength and the ultimate tensile strength of the aged material were better than for the solution-annealed one, and only slightly decreased with increasing temperature when tested between room temperatures and 650 °C. In this range of temperature, the fracture surface of aged material evolves from purely intergranular to purely transgranular due to the thermal activation of dislocation mobility that relieves the stress at the grain boundaries, while the rupture of the solution annealed material is due to the coalescence of voids induced by decohesion at the MC carbides/matrix interface. At higher temperatures, precipitation of γ’ particles upon testing of the solution-annealed material leads to a temperature-dependent increase in both yield strength and ultimate tensile strength, which nevertheless remain below the aged material ones with the exception of the higher temperatures. At the same time, an overall decrease of the aged material mechanical properties is observed. Minimum ductility was observed at 750 °C for both solution annealed and aged specimen, due to the oxidation of grain boundaries leading to an environmentally-induced fracture mechanism. At higher temperatures, dynamic recovery and dynamic recrystallization occur which prevents such a rupture mechanism, but finally leads to rupture by grain boundary slipping at 900 °C.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Marsh, C. and Depinoy, S. and Kaoumi, D.}, year={2016}, month={Nov}, pages={474–484} } @inproceedings{kaoumi_garde_pan_2016, title={In-situ ion irradiation of ZIRLO® alloy}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85019028888&partnerID=MN8TOARS}, booktitle={Top Fuel 2016: LWR Fuels with Enhanced Safety and Performance}, author={Kaoumi, D. and Garde, A. and Pan, G.}, year={2016}, pages={417–424} } @inproceedings{marsh_kaoumi_2016, title={Tensile behavior of inconel X750 Sheets: Effect of heat treatment}, volume={115}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85029410263&partnerID=MN8TOARS}, booktitle={Transactions of the American Nuclear Society}, author={Marsh, C. and Kaoumi, D.}, year={2016}, pages={469–472} } @article{huang_abad_ramsey_de figueiredo_kaoumi_li_asta_gronbech-jensen_hosemann_2016, title={A high temperature mechanical study on PH 13-8 Mo maraging steel}, volume={651}, ISSN={0921-5093}, url={http://dx.doi.org/10.1016/J.MSEA.2015.10.077}, DOI={10.1016/J.MSEA.2015.10.077}, abstractNote={High temperature mechanical measurements were conducted to study the effect of the dynamic precipitation process of PH 13-8 Mo maraging steel. Yield stress, ultimate tensile strength, total elongation, hardness, strain rate sensitivity and activation volume were evaluated as a function of the temperature. The dynamic changes in the mechanical properties at different temperatures were evaluated and a balance between precipitation hardening and annealed softening is discussed. A comparison between hardness and yield stress and ultimate tensile strength over a temperature range from 300 to 600 °C is made. The behavior of the strain rate sensitivity was correlated with the intermetallic precipitates formed during the experiments.}, journal={Materials Science and Engineering: A}, publisher={Elsevier BV}, author={Huang, Z. and Abad, M.D. and Ramsey, J.K. and de Figueiredo, M. Rebelo and Kaoumi, D. and Li, N. and Asta, M. and Gronbech-Jensen, N. and Hosemann, P.}, year={2016}, month={Jan}, pages={574–582} } @article{allen_kaoumi_wharry_jiao_topbasi_kohnert_barnard_certain_field_was_et al._2015, title={Characterization of microstructure and property evolution in advanced cladding and duct: Materials exposed to high dose and elevated temperature}, volume={30}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84929692498&partnerID=MN8TOARS}, DOI={10.1557/jmr.2015.99}, abstractNote={Abstract}, number={9}, journal={Journal of Materials Research}, author={Allen, T.R. and Kaoumi, D. and Wharry, J.P. and Jiao, Z. and Topbasi, C. and Kohnert, A. and Barnard, L. and Certain, A. and Field, K.G. and Was, G.S. and et al.}, year={2015}, pages={1246–1274} } @inproceedings{kaoumi_liu_paul_2015, title={Deformation induced martensitic transformation in 304 ss}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84962758624&partnerID=MN8TOARS}, booktitle={PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015}, author={Kaoumi, D. and Liu, J. and Paul, F.-L.}, year={2015}, pages={629–630} } @article{catalini_kaoumi_reynolds_grant_2015, title={Dispersoid Distribution and Microstructure in Fe-Cr-Al Ferritic Oxide Dispersion-Strengthened Alloy Prepared by Friction Consolidation}, volume={46}, ISSN={1073-5623 1543-1940}, url={http://dx.doi.org/10.1007/S11661-015-3059-1}, DOI={10.1007/S11661-015-3059-1}, number={10}, journal={Metallurgical and Materials Transactions A}, publisher={Springer Science and Business Media LLC}, author={Catalini, David and Kaoumi, Djamel and Reynolds, Anthony P. and Grant, Glenn J.}, year={2015}, month={Jul}, pages={4730–4739} } @article{kaoumi_weber_hattar_ribis_2015, title={Introduction}, volume={30}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84940886237&partnerID=MN8TOARS}, DOI={10.1557/jmr.2015.133}, number={9}, journal={Journal of Materials Research}, author={Kaoumi, D. and Weber, W.J. and Hattar, K. and Ribis, J.}, year={2015}, pages={1157} } @article{topbasi_kaoumi_motta_kirk_2015, title={Microstructural evolution in NF616 (P92) and Fe–9Cr–0.1C-model alloy under heavy ion irradiation}, volume={466}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/J.JNUCMAT.2015.07.003}, DOI={10.1016/J.JNUCMAT.2015.07.003}, abstractNote={In this comparative study, in situ investigations of the microstructure evolution in a Fe–9Cr ferritic–martensitic steel, NF616, and a Fe–9Cr–0.1C-model alloy with a similar ferritic–martensitic microstructure have been performed. NF616 and Fe–9Cr–0.1C-model alloy were irradiated to high doses (up to ∼10 dpa) with 1 MeV Kr ions between 50 and 673 K. Defect cluster density increased with dose and saturated in both alloys. The average size of defect clusters in NF616 was constant between 50 and 573 K, on the other hand average defect size increased with dose in Fe–9Cr–0.1C-model alloy around ∼1 dpa. At low temperatures (50–298 K), alignment of small defect clusters resulted in the formation of extensive defects in Fe–9Cr–0.1C-model alloy around ∼2–3 dpa, while similar large defects in NF616 started to form at a high temperature of 673 K around ∼5 dpa. Interaction of defect clusters with the lath boundaries were found to be much more noticeable in Fe–9Cr–0.1C-model alloy. Differences in the microstructural evolution of NF616 and Fe–9Cr–0.1C-model alloy are explained by means of the defect cluster trapping by solute atoms which depends on the solute atom concentrations in the alloys.}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Topbasi, Cem and Kaoumi, Djamel and Motta, Arthur T. and Kirk, Mark A.}, year={2015}, month={Nov}, pages={179–186} } @article{vo_reichardt_howard_abad_kaoumi_chou_hosemann_2015, title={Small-Scale Mechanical Testing on Proton Beam-Irradiated 304 SS from Room Temperature to Reactor Operation Temperature}, volume={67}, ISSN={1047-4838 1543-1851}, url={http://dx.doi.org/10.1007/S11837-015-1596-0}, DOI={10.1007/S11837-015-1596-0}, number={12}, journal={JOM}, publisher={Springer Science and Business Media LLC}, author={Vo, H. and Reichardt, A. and Howard, C. and Abad, M. D. and Kaoumi, D. and Chou, P. and Hosemann, P.}, year={2015}, month={Aug}, pages={2959–2964} } @article{kaoumi_gautier_adamson_kirk_2015, title={Using In-Situ TEM to Characterize the Microstructure Evolution of Metallic Systems under External Solicitation}, volume={21}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/S143192761500135X}, DOI={10.1017/S143192761500135X}, abstractNote={Studying materials under external stimulus such as irradiation and/or mechanical stress can be difficult because of the lack of kinetics information, since usually samples are examined ex situ (e.g. after irradiation or after mechanical testing) so that only discrete snapshots of the process are available. Given the dynamic nature of the phenomena, direct in situ observation is often necessary to better understand the mechanisms, kinetics and driving forces of the processes involved. For this matter, using in situ Transmission Electron Microscopy (TEM) can be of great help[1]. Indeed, the spatial resolution of the TEM makes it an invaluable tool in which one can continuously track the real-time response of the microstructure to external stimuli, which can help discover and quantify the fundamental rate-limiting microscopic processes and mechanisms governing the macroscopic properties. In this presentation, two examples will be given which show how the technique can be used for nuclear engineering applications. (i) In-situ straining experiments in the TEM is applied to investigate deformation mechanisms in Ni-based alloys (Inconel 617 and Haynes 230) which are candidate materials for the heat exchanger in the GEN-IV Very High Temperature nuclear Reactor. In addition to showing dislocation dynamics under tensile strain, it also allows to follow crack propagation as it proceeds in the material. (ii) In-situ Ion-irradiation in the TEM has proven a very good tool for studying the basic mechanisms of radiation damage formation and evolution as a function of dose, dose rate, temperature and ion type.}, number={S3}, journal={Microscopy and Microanalysis}, publisher={Cambridge University Press (CUP)}, author={Kaoumi, D. and Gautier, T. and Adamson, J. and Kirk, M.}, year={2015}, month={Aug}, pages={111–112} } @article{kaoumi_adamson_2014, title={Self-ordered defect structures in two model F/M steels under in situ ion irradiation}, volume={448}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/J.JNUCMAT.2014.01.048}, DOI={10.1016/J.JNUCMAT.2014.01.048}, abstractNote={Two model F/M steels, 9Cr-model and 12Cr-model, were irradiated with 1 MeV Kr ions in situ in a TEM at temperatures between 20 K and 573 K to doses as high as 15 dpa. During the early stages of irradiation of the two F/M steels, defect clusters were rather uniformly distributed within grains, and a saturation density was quickly reached. However, at higher doses, self-ordering alignments of defect clusters were found in some grains. The regularly ordered arrays of small loops were observed in the two F/M steels along 〈1 1 0〉 directions with spacing about 30–50 nm. Once the aligned structure was created, it was stable under further irradiation. The possible mechanisms for the "self-organization"/"ordering" of the clusters were investigated. This paper describes the process and its temperature dependence, and the possible mechanisms are discussed.}, number={1-3}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Kaoumi, D. and Adamson, J.}, year={2014}, month={May}, pages={233–238} } @article{kaoumi_hrutkay_2014, title={Tensile deformation behavior and microstructure evolution of Ni-based superalloy 617}, volume={454}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/J.JNUCMAT.2014.08.003}, DOI={10.1016/J.JNUCMAT.2014.08.003}, abstractNote={The mechanisms of deformation were investigated in a nickel-based alloy (Inconel 617) of interest for the Intermediate Heat Exchanger (IHX) for the very high temperature reactor (VHTR). Tensile tests at 25 °C, 600 °C, 800 °C, and 950 °C were conducted in air at different strain rates. The tests were followed by electron microscopy analysis (including FE-SEM, TEM, EDX). The tensile property measurements and the metallographic examination of tested specimens allowed relating the deformation behavior with the microstructural changes in the material. The temperature and strain rate impact on the properties was assessed. The results and microstructure observations were discussed in terms of serrated flow associated with dynamic strain ageing, precipitate evolution, and softening processes due to dynamic recrystallization.}, number={1-3}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Kaoumi, D. and Hrutkay, K.}, year={2014}, month={Nov}, pages={265–273} } @article{hrutkay_kaoumi_2014, title={Tensile deformation behavior of a nickel based superalloy at different temperatures}, volume={599}, ISSN={0921-5093}, url={http://dx.doi.org/10.1016/J.MSEA.2014.01.056}, DOI={10.1016/J.MSEA.2014.01.056}, abstractNote={Ni-based alloy Haynes 230 is of interest for high temperature applications (e.g. Intermediate Heat eXchanger (IHX)) because of its high temperature strength and oxidation resistance. In this work, the temperature dependence of the tensile behavior of the alloy and the strain rate effect was studied by tensile tests in the temperature range of 25–950 °C, at strain rates of 10−3 s−1, 10−4 s−1, and 10−5 s−1. The tensile strength decreased with increasing temperature regardless of the strain rate. The total elongation at rupture fluctuated more with temperature. The alloy showed an abnormal variation of the yield stress with increasing temperature i.e. the yield strength decreased slightly with temperature up to about 600 °C and then increased between 600 and 850 °C followed by a rapid decrease. This Yield Stress Anomaly (YSA) was however absent at the slowest strain rate of 10−5 s−1. SEM and TEM characterization was performed on fractured specimens to determine the predominant deformation mechanisms accounting for the observed Yield Stress Anomaly. Also, serrations were observed in the stress–strain curves at temperatures above 300 °C, the shape and amplitude of which depended on temperature and strain rate. The analysis of the stress–strain curves coupled with the microstructure investigation of the fractured samples showed that two different deformation mechanisms occur depending on the temperature and strain rate. The saw-tooth type serrations at intermediate temperatures and higher strain rates were associated with dynamic strain aging whereas the oscillations with a sinusoidal shape were associated with dynamic recrystallization at temperatures higher than 800 °C and slower strain rates.}, journal={Materials Science and Engineering: A}, publisher={Elsevier BV}, author={Hrutkay, K. and Kaoumi, D.}, year={2014}, month={Apr}, pages={196–203} } @article{kaoumi_adamson_kirk_2014, title={Microstructure evolution of two model ferritic/martensitic steels under in situ ion irradiation at low doses (0–2dpa)}, volume={445}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/J.JNUCMAT.2013.10.047}, DOI={10.1016/J.JNUCMAT.2013.10.047}, abstractNote={Ferritic/martensitic steels are candidate materials for structural and cladding components designed for Generation IV reactors because of their superior resistance to radiation damage at the high operating temperatures envisioned in these reactors. To enable the development and optimization of such advanced alloys for in-reactor use, a fundamental understanding of radiation damage accumulation in materials is required. In this work, two model F/M steels (12Cr model alloy and 9Cr model alloy) were irradiated with 1 MeV Kr ions at 50 K, 180 K, 298 K, 473 K and 573 K in situ in a TEM. The microstructure evolution under irradiation was followed and characterized at successive doses in terms of irradiation-induced defect formation and evolution, defect density, size distribution and interaction with the as-fabricated microstructure (e.g. dislocation networks, lath boundaries) using weak-beam dark-field imaging. The effect of the irradiation temperature on the defect kinetics is assessed at doses up to 2 dpa.}, number={1-3}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Kaoumi, D. and Adamson, J. and Kirk, M.}, year={2014}, month={Feb}, pages={12–19} } @inproceedings{goddard_kaoumi_2013, title={Precipitate characterization in two ODS steels using synchrotron XRD of consolidated samples and Cu-Kα XRD of precipitate extractions}, volume={109}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84902780874&partnerID=MN8TOARS}, number={PART 1}, booktitle={Transactions of the American Nuclear Society}, author={Goddard, J. and Kaoumi, D.}, year={2013}, pages={576–579} } @inproceedings{hrutkay_kaoumi_2013, title={Tensile behavior of inconel 617 vs. Haynes 230: Effects of temperature and strain rate}, volume={109}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84902821147&partnerID=MN8TOARS}, number={PART 1}, booktitle={Transactions of the American Nuclear Society}, author={Hrutkay, K. and Kaoumi, D.}, year={2013}, pages={644–647} } @article{catalini_kaoumi_reynolds_grant_2013, title={Friction Consolidation of MA956 powder}, volume={442}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/j.jnucmat.2012.11.054}, DOI={10.1016/j.jnucmat.2012.11.054}, abstractNote={The applicability of Friction Consolidation (FC) to process an oxide dispersion strengthened (ODS) steel was studied to tackle the downsides of the conventional processing route (high complexity, extremely high raw material final cost). In this work, MA956 ODS powders have been consolidated through the FC process and small compacts of low porosity have been achieved with the desired oxide dispersion. The friction-consolidated sample shows a range of grain sizes when measuring at different locations within the cross section of the sample, and the values were all finer than those of a conventionally-processed sample. With regard to shape, grains in the friction-consolidated sample show an equiaxed cross section. Three particle families were observed: Y–Al–O, Al–O and Ti(C, N). The Y–Al–O and the Al–O were observed in both the conventionally- and the friction-consolidated sample. This result points out the ability to achieve the precipitation of the Y–Al–O by FC. The Ti(C, N) particles were only observed in the conventionally processed sample. The transmission electron microscopy images showed regions with smaller particles on the friction-consolidated sample. However, due to the extremely localized nature of the measurement, more data should be generated and analyzed to make this observation more statistically reliable.}, number={1-3}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Catalini, David and Kaoumi, Djamel and Reynolds, Anthony P. and Grant, Glenn J.}, year={2013}, month={Nov}, pages={S112–S118} } @inproceedings{catalini_kaoumi_reynolds_grant_2012, title={Friction consolidation of an oxide dispersion strengthened steel}, volume={107}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84876557879&partnerID=MN8TOARS}, booktitle={Transactions of the American Nuclear Society}, author={Catalini, D. and Kaoumi, D. and Reynolds, A. and Grant, G.}, year={2012}, pages={458–461} } @article{kaoumi_motta_kirk_faney_wirth_bentley_2010, title={In Situ TEM Studies of Microstructure Evolution Under Ion Irradiation for Nuclear Engineering Applications}, volume={16}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/S143192761006321X}, DOI={10.1017/S143192761006321X}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.}, number={S2}, journal={Microscopy and Microanalysis}, publisher={Cambridge University Press (CUP)}, author={Kaoumi, D and Motta, AT and Kirk, M and Faney, T and Wirth, B and Bentley, J}, year={2010}, month={Jul}, pages={1606–1607} } @article{kirk_baldo_liu_ryan_birtcher_yao_xu_jenkins_hernandez-mayoral_kaoumi_et al._2009, title={In situ transmission electron microscopy and ion irradiation of ferritic materials}, volume={72}, ISSN={1059-910X 1097-0029}, url={http://dx.doi.org/10.1002/jemt.20670}, DOI={10.1002/jemt.20670}, abstractNote={AbstractThe intermediate voltage electron microscope‐tandem user facility in the Electron Microscopy Center at Argonne National Laboratory is described. The primary purpose of this facility is electron microscopy with in situ ion irradiation at controlled sample temperatures. To illustrate its capabilities and advantages a few results of two outside user projects are presented. The motion of dislocation loops formed during ion irradiation is illustrated in video data that reveals a striking reduction of motion in Fe‐8%Cr over that in pure Fe. The development of extended defect structure is then shown to depend on this motion and the influence of nearby surfaces in the transmission electron microscopy thin samples. In a second project, the damage microstructure is followed to high dose (200 dpa) in an oxide dispersion strengthened ferritic alloy at 500°C, and found to be qualitatively similar to that observed in the same alloy neutron irradiated at 420°C. Microsc. Res. Tech., 2009. © 2009 Wiley‐Liss, Inc.}, number={3}, journal={Microscopy Research and Technique}, publisher={Wiley}, author={Kirk, Marquis A. and Baldo, Peter M. and Liu, Amelia C.Y. and Ryan, Edward A. and Birtcher, Robert C. and Yao, Zhongwen and Xu, Sen and Jenkins, Michael L. and Hernandez-Mayoral, Mercedes and Kaoumi, Djamel and et al.}, year={2009}, month={Mar}, pages={182–186} } @article{bentley_hoelzer_busby_certain_allen_kaoumi_motta_kirk_2009, title={TEM Characterization of Crept and Irradiated Nano-structured Ferritic Alloys}, volume={15}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/S1431927609095828}, DOI={10.1017/S1431927609095828}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009}, number={S2}, journal={Microscopy and Microanalysis}, publisher={Cambridge University Press (CUP)}, author={Bentley, J and Hoelzer, DT and Busby, JT and Certain, AG and Allen, TR and Kaoumi, D and Motta, AT and Kirk, MA}, year={2009}, month={Jul}, pages={1350–1351} } @article{kaoumi_motta_birtcher_2008, title={A thermal spike model of grain growth under irradiation}, volume={104}, ISSN={0021-8979}, url={http://dx.doi.org/10.1063/1.2988142}, DOI={10.1063/1.2988142}, abstractNote={The experimental study of grain growth in nanocrystalline metallic foils under ion irradiation showed the existence of a low-temperature regime (below about 0.15–0.22Tm), where grain growth is independent of the irradiation temperature, and a thermally assisted regime where grain growth is enhanced with increasing irradiation temperature. A model is proposed to describe grain growth under irradiation in the temperature-independent regime, based on the direct impact of the thermal spikes on grain boundaries. In the model, grain-boundary migration occurs by atomic jumps, within the thermal spikes, biased by the local grain-boundary curvature driving. The jumps in the spike are calculated based on Vineyard’s analysis of thermal spikes and activated processes using a spherical geometry for the spike. The model incorporates cascade structure features such as subcascade formation, and the probability of subcascades occurring at grain boundaries. This results in a power law expression relating the average grain size with the ion dose with an exponent equal to 3, in agreement with the experimental observations. The model is applied to grain growth observed in situ in a transmission electron microscope in a wide range of doses, temperature, and irradiation conditions for four different pure metals, and shown to predict well the results in all applicable cases. Some discussions are also presented on the expansion of the model to the thermally assisted regime. The paper is organized in six sections. Section I gives background and literature review, while Secs. II and III review experimental methods and results for in situ grain growth under irradiation. Section IV derives the model proposed to find the grain-growth equation in the nonthermal regime, and in Sec. V the model is applied to the results. In Sec. VI grain growth in the thermally assisted regime is discussed and Sec. VII presents the conclusions.}, number={7}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kaoumi, D. and Motta, A. T. and Birtcher, R. C.}, year={2008}, pages={073525} } @inproceedings{kaoumi_motta_kirk_2008, title={Characterization and in-situ ion-irradiation of MA957 ODS steel}, volume={98}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-55249124982&partnerID=MN8TOARS}, booktitle={Transactions of the American Nuclear Society}, author={Kaoumi, D. and Motta, A. and Kirk, M.}, year={2008}, pages={1113–1114} } @inproceedings{kaoumi_motta_birtcher_2008, title={Grain growth in nanocrystalline metal thin films under in situ ion-beam irradiation}, volume={1492 STP}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-62849116960&partnerID=MN8TOARS}, booktitle={ASTM Special Technical Publication}, author={Kaoumi, D. and Motta, A.T. and Birtcher, R.C.}, year={2008}, pages={206–218} } @article{kaoumi_motta_birtcher_2008, title={Influence of alloying elements on grain-growth in Zr(Fe) and Cu(Fe) thin-films under in situ ion-irradiation}, volume={382}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/j.jnucmat.2008.08.011}, DOI={10.1016/j.jnucmat.2008.08.011}, abstractNote={Thin-films of Zr(Fe) and Cu(Fe) were ion-irradiated in situ in a transmission electron microscope to study the influence of alloying elements on grain-growth. These two systems are different in that Zr–Fe has a negative heat of mixing and Cu–Fe a positive heat of mixing. Irradiations conducted at temperatures of 20–573 K showed precipitation in Zr(Fe) but not in Cu(Fe). The grain sizes increased monotonically with fluence and in both cases the pure metal exhibited more grain-growth than the alloy. A more drastic reduction of grain-growth rate was observed in Zr(Fe) (where precipitate drag occurred) than in Cu–Fe (where only solute drag was available). Zr(Fe) samples were also subjected to 1 MeV electron irradiation but no grain-growth was observed. The results are discussed in terms of the mechanisms of grain-growth under irradiation.}, number={2-3}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Kaoumi, D. and Motta, A.T. and Birtcher, R.C.}, year={2008}, month={Dec}, pages={184–189} } @article{kaoumi_motta_birtcher_2007, title={Grain growth in nanocrystalline metal thin films under in situ ion-beam irradiation}, volume={4}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34948911544&partnerID=MN8TOARS}, DOI={10.1520/JAI100743}, abstractNote={Abstract In-situ observations in a transmission electron microscope (TEM) were used to study the microstructure evolution in metal Zr, Pt, Cu, and Au nanocrystalline thin films under ion-beam irradiation. Free-standing films were prepared by sputter deposition. Samples were irradiated in-situ at the Intermediate Voltage Electron Microscope (IVEM) at Argonne National Laboratory with Ar and Kr ions to fluences in excess of 1016 ion/cm2. As a result of irradiation, grain growth was observed in all samples using Bright Field (BF) imaging in the TEM. The average grain size increased monotonically with ion fluence until it reached a saturation value. Similarly to thermal grain growth, the ion-irradiation induced grain growth curves could be best fitted with curves of the type: Dn-D0n=KΦ. The irradiations were done at temperatures ranging from 20 to 773 K. The results suggest the existence of three regimes with respect to irradiating temperature: (i) a purely thermal regime, which appears to start above the bulk coarse-grained recrystallization temperature, (ii) a thermally assisted regime where thermal diffusion and irradiation effects combine to increase the rate of grain growth relative to that resulting from either of these mechanisms alone, and (iii) an athermal regime (low-temperature regime) where irradiation can by itself cause grain growth. The transition temperature between the athermal regime and the thermally assisted regime depends on the material, but is in the range 0.14–0.22 times the melting point. The influence of the ion type was also investigated on Zr-Fe irradiated with 600 keV Kr ions versus 600 keV Ar ions.}, number={8}, journal={Journal of ASTM International}, author={Kaoumi, D. and Motta, A.T. and Birtcher, R.C.}, year={2007} } @article{kaoumi_motta_birtcher_2006, title={Grain growth in Zr–Fe thin films during in situ ion irradiation in a TEM}, volume={242}, ISSN={0168-583X}, url={http://dx.doi.org/10.1016/j.nimb.2005.08.158}, DOI={10.1016/j.nimb.2005.08.158}, abstractNote={In situ ion-beam irradiation was used to study irradiation induced grain growth in co-sputter-deposited Zr/xFe (0% ⩽ x ⩽ 4.5%) nanocrystalline thin films. Samples were irradiated with 500 keV Kr ions to fluences in excess of 1016 ions/cm2 (on the order of 80–100 dpa), at irradiation temperatures ranging from 20 K to 573 K. The average grain size increased monotonically with ion fluence until it reached a saturation value which depends both on temperature and on the presence of Fe. Similarly to thermal grain growth, the ion irradiation induced grain growth curves could be best fitted with curves of the type: Ln-L0n=KΦ. Grain growth at 20 K is similar to that which occurs at 298 K. Above 298 K, the rate of grain growth increases with irradiation temperature.}, number={1-2}, journal={Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms}, publisher={Elsevier BV}, author={Kaoumi, D. and Motta, A.T. and Birtcher, R.C.}, year={2006}, month={Jan}, pages={490–493} } @inproceedings{kaoumi_motta_birtcher_2005, title={Irradiation-enhanced second-phase precipitation in Zr-Fe nanocrystalline thin films}, volume={908}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34249950175&partnerID=MN8TOARS}, DOI={10.1557/proc-0908-oo04-04}, abstractNote={AbstractIn situ observations in a transmission electron microscope (TEM) were used to study ion-beam enhancement of second-phase precipitation in Zr-Fe nanocrystalline thin films. The free-standing films were prepared by co-sputter deposition with an Fe content of 1.2 at%. TEM diffraction analysis showed that only the hcp Zr crystal structure was present in the as-deposited films. No second phases were detected, although Rutherford Backscattering Spectroscopy (RBS) confirmed a Fe content beyond the solubility limit of Fe in Zr (of the order of ppm). This means the thin films were Zr solid solutions supersaturated with Fe. Heat treatment in the absence of irradiation was observed to cause precipitation of the Zr2Fe intermetallic phase, but only above 673 K. The same second-phase precipitation can occur at lower temperatures in the presence of ion irradiation. Samples were irradiated in-situ at the Intermediate Voltage Electron Microscope (IVEM) at Argonne National Laboratory with Kr ions to fluences in excess of 1016 ion/cm2, at temperatures ranging from 50 to 573 K. Second phase precipitation was detected by electron diffraction patterns and by dark field imaging comparing regions exposed to the beam with regions protected from the beam by the TEM support grid. Precipitation of Zr2Fe intermetallic phase was observed at all irradiating temperatures above room temperature. In the bulk, this phase is thermodynamically metastable in the range of temperatures investigated (relative to the orthorhombic Zr3Fe intermetallic phase). The kinetics of the irradiation-enhanced second-phase precipitation was followed by recording the diffraction patterns at regular intervals. The dose to precipitation was found to decrease with increasing irradiation temperature.}, booktitle={Materials Research Society Symposium Proceedings}, author={Kaoumi, D. and Motta, A.T. and Birtcher, R.C.}, year={2005}, pages={7–12} }