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Rogozkin, S.; Chernobaeva, A.; Aleev, A.; Nikitin, A.; Zaluzhnyi, A.; Erak, D.; Shtrombakh, Ya.; Zabusov, O.; Debarberis, L.; Zeman, A. |
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The Effect of Post-Irradiation Annealing on VVER-440 RPV Materials Mechanolocal Properties and Nano-Structure Under Re-Irradiation |
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2009 |
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ASME Conference Proceedings |
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ASME Conf. Proc. |
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2009 |
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43703 |
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Summary Language |
553-562 |
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The present work provides the analyses of embrittlement behavior and atom probe tomography study of nano-structure evolution of VVER-440 RPV materials under irradiation and re-irradiation. Specimens from VVER-440 weld with high level of cupper (0.16 wt.%) and phosphorus (0.027–0.038 wt.%) were irradiated in surveillance channels of Rovno Nuclear Power plant unit 1 (Ro-1). The embrittlement behavior has been assessed by transition temperature shift. |
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NU @ karnesky @ |
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10983 |
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Lee, Woei-Shyan; Chen, Tao-Hsing; Lin, Chi-Feng; Chen, Ming-Shiang |
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Impact deformation behaviour and dislocation substructure of Al-Sc alloy |
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Journal Article |
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2010 |
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Journal of Alloys and Compounds |
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493 |
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1-2 |
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580-589 |
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Al-Sc alloy; Strain rate sensitivity; Activation volume; Adiabatic shear band; Dislocation; Precipitates |
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This paper employs a compressive split-Hopkinson pressure bar to investigate the impact deformation behaviour of Al-Sc alloy under high strain rates of 1.2103s-1, 3.2103s-1 and 5.8103s-1, respectively, and temperatures of -100C, 25C and 300C. It is shown that for a constant temperature, the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, while the activation volume decreases. Conversely, for a constant strain rate, the flow stress, work hardening rate and strain rate sensitivity decrease with increasing temperature, while the activation volume increases. It is found that the impact deformation behaviour of Al-Sc alloy can be accurately described using the Zerilli-Armstrong constitutive equation. Optical microscopy (OM) observations reveal that the specimens fail principally as the result of an adiabatic shearing mechanism. Furthermore, scanning electron microscopy (SEM) observations show that the fracture surfaces are characterised by a dimple-like structure, which indicates a ductile failure mode. Transmission electron microscopy (TEM) observations indicate that the dislocation density and cell size are related to the strain rate, flow stress and temperature. Finally, the TEM observations suggest that the strengthening effect observed in the deformed Al-Sc alloy is the result of Al3Sc precipitates within the matrix and at the grain boundaries, which suppress dislocation motion and prompt an increase in the work hardening stress. |
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0925-8388 |
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NU @ karnesky @ |
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10784 |
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Lee, S.-W.; Yeh, J.-W. |
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Superplasticity of 5083 alloys with Zr and Mn additions produced by reciprocating extrusion |
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2007 |
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Materials Science and Engineering: A |
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460-461 |
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409-419 |
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Aluminum alloys; Extrusion; Superplasticity |
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In this study, 5083 aluminum alloys modified with grain refiner, 0.25% Zr and 0.46% Mn, were processed by reciprocating extrusion to yield high-strain-rate superplasticity above 400 [degree sign]C and superior room-temperature mechanical properties. Without any prior homogenization treatment, 10 extrusion passes could give the cast billets an equiaxed grain structure with a grain size of about 4.5 [mu]m and a subgrain size about 0.2 [mu]m, and a uniform distribution of fine inclusions and dispersoids in the matrix. The fine-grained structure was stable up to 525 [degree sign]C, giving the alloy a high-strain-rate and low-stress superplasticity over a wide operating temperature of 400-500 [degree sign]C. In the tensile test at 500 [degree sign]C, a maximum elongation of 1013% and a low flow stress of 7.7 MPa at 5 x 10-2 s-1 were achieved. The apparent and true activation energies for low temperatures (300-400 [degree sign]C) without high-strain-rate superplasticity were 220.6 and 208 kJ/mol, respectively, whereas those at high temperatures (400-500 [degree sign]C) were 88.4 and 98.7 kJ/mol, respectively. Further analysis confirms that grain boundary sliding is the dominant mechanism over the high-strain-rate region from 1 x 10-2 to 5 x 10-1 s-1 at 500 [degree sign]C, and power-law breakdown mechanism occurs over the strain rate from 5 x 10-4 to 1 x 10-2 s-1 at 300 [degree sign]C. The high-strain-rate superplasticity was more strongly enhanced by Zr addition than addition of Cr and Mn. Two enhancing mechanisms for the maximum superplastic elongation and the optimum strain rate are proposed. This study concludes that the effectiveness of Zr is caused by the fineness and the coherency of Zr-rich dispersoids in the matrix. |
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NU @ karnesky @ |
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9637 |
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Lee, Z.; Witkin, D.B.; Radmilovic, V.; Lavernia, E.J.; Nutt, S.R. |
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Bimodal microstructure and deformation of cryomilled bulk nanocrystalline Al-7.5Mg alloy |
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Journal Article |
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2005 |
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Materials Science and Engineering: A |
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The Langdon Symposium: Flow and forming of Crystalline Materials |
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410-411 |
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462-467 |
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Nanocrystalline; Bimodal; Cryomilling; Aluminum; Deformation |
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The microstructure, mechanical properties and deformation response of bimodal structured nanocrystalline Al-7.5Mg alloy were investigated. Grain refinement was achieved by cryomilling of atomized Al-7.5Mg powders, and then cryomilled nanocrystalline powders blended with 15 and 30% unmilled coarse-grained powders were consolidated by hot isostatic pressing followed by extrusion to produce bulk nanocrystalline alloys. Bimodal bulk nanocrystalline Al-7.5Mg alloys, which were comprised of nanocrystalline grains separated by coarse-grain regions, show balanced mechanical properties of enhanced yield and ultimate strength and reasonable ductility and toughness compared to comparable conventional alloys and nanocrystalline metals. The investigation of tensile and hardness test suggests unusual deformation mechanisms and interactions between ductile coarse-grain bands and nanocrystalline regions. |
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NU @ karnesky @ |
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10321 |
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Rogozhkin, S.V.; Aleev, A.A.; Zaluzhnyi, A.G.; Nikitin, A.A.; Iskandarov, N.A.; Vladimirov, P.; Lindau, R.; Möslang, A. |
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Atom probe characterization of nano-scaled features in irradiated ODS Eurofer steel |
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Journal Article |
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2011 |
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Journal of Nuclear Materials |
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409 |
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94-99 |
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ODS steel; ODS Eurofer; clusters; irradiation; fast neutron |
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Our previous investigations of unirradiated ODS Eurofer by tomographic atom probe (TAP) revealed numerous nano-scaled features (nanoclusters) enriched in vanadium, yttrium and oxygen. In this work the effect of neutron irradiation on nanostructure behaviour of ODS Eurofer (9%-CrWVTa) was investigated. The irradiation was performed in the research reactor BOR-60 (Dimitrovgrad, Russia) where materials were irradiated at 330°S to 32 dpa. TAP studies were performed on the needles prepared from parts of broken Charpy specimens. For all specimens except one, which was tested at 500°C, the Charpy tests were performed at temperatures not exceeding the irradiation temperature. A high number density 2÷4×1024 m-3 of ultra fine 1-3 nm diameter nanoclusters enriched in yttrium, oxygen, manganese and chromium was observed in the as-irradiated state. The composition of detected clusters differs from that for unirradiated ODS Eurofer. It was observed in this work that after neutron irradiation vanadium atoms had left the clusters, moving from the core into solid solution. The concentrations of yttrium and oxygen in the matrix, as it was detected, increase several times under irradiation. In the samples tested at 500°C both the number density of clusters and the yttrium concentration in the matrix decrease by a factor of two. |
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0022-3115 |
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NU @ karnesky @ |
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10946 |
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Aleev, A.A.; Iskandarov, N.A.; Klimenkov, M.; Lindau, R.; Möslang, A.; Nikitin, A.A.; Rogozhkin, S.V.; Vladimirov, P.; Zaluzhnyi, A.G. |
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Investigation of oxide particles in unirradiated ODS Eurofer by tomographic atom probe |
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Journal Article |
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2011 |
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Journal of Nuclear Materials |
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409 |
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65-71 |
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Ods; atom probe tomography; precipitation |
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Oxide dispersion strengthened steels possess better high-temperature creep and radiation resistance than conventionally produced ferritic/martensitic steels. This behavior is mainly caused by the presence of highly dispersed and extremely stable oxide particles with diameters of a few nanometers. In this work the nanostructure of ODS Eurofer steel was investigated by means of tomographic atom probe and correlations with recent TEM and SANS studies were derived. The present investigation revealed nanoscaled clusters of typically 2 nm diameter containing not only yttrium and oxygen but also vanadium and nitrogen. Moreover, concentration of vanadium in particles was found to be higher than that of yttrium, which indicates the importance of these elements in cluster formation. The estimated average cluster number density is about 2×1024 m-3. These enriched zones might be evidently attributed to precursors of the larger precipitates observed by TEM. This conclusion is also supported by the similarities of the chemical composition inside enriched zones seen in both atomic probe and TEM data. |
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0022-3115 |
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NU @ karnesky @ |
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10951 |
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Park, Kyung-Tae; Hwang, Duck-Young; Lee, Young-Kook; Kim, Young-Kuk; Shin, Dong Hyuk |
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High strain rate superplasticity of submicrometer grained 5083 Al alloy containing scandium fabricated by severe plastic deformation |
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Journal Article |
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2003 |
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Materials Science and Engineering A |
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Mater. Sci. Eng. A |
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341 |
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273-281 |
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High strain rate superplasticity; 5083 Al alloy; Scandium; Severe plastic deformation; Ultrafine grains |
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High strain rate superplasticity (HSRS) was obtained in a commercial 5083 Al alloy by introducing a ultrafine grained structure of 0.3 small mu, Greekm through severe plastic deformation and by adding a dilute amount of scandium (Sc) as a microstructure stabilizer. Tensile tests were carried out on the as-processed sample at temperatures of 623–823 K and initial strain rates of 1×10−3–1×100 s−1. The maximum elongation to failure of 740% was obtained at 773 K and 1×10−2 s−1. HSRS of the alloy was attributed to the combined effects of dynamic recrystallization and preservation of fine recrystallized grains by the presence of Sc. The mechanical behavior of the alloy at 773 K was characterized by a sigmoidal behavior in a plot of stress vs strain rate in the double logarithmic scale. The origin of the sigmoidal behavior was discussed in terms of microstructural evolution during superplastic deformation. An examination of the fractured samples revealed that failure occurred in a brittle manner related to cavitation rather than necking. Cavity stringers were formed parallel to the tensile axis by interlinkage of jagged-shaped isolated cavities along grain boundaries aligned to the tensile axis. |
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NU @ karnesky @ |
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585 |
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Derraa, A.; Lee, G., M J |
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Configuration and electronic structure of silver overlayers on microscopic (110) facets of tungsten |
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Journal Article |
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1995 |
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Surface Science |
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Surf. Sci. |
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329 |
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1-13 |
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3001 |
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Gaudin, G. A.; Lee, G., M J |
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Aggregates of chemisorbed copper on the (110) and (100) surfaces of tungsten: electronic structure |
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Journal Article |
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1994 |
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Surface Science |
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Surf. Sci. |
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310 |
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34-44 |
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Field Emission |
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3028 |
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Lagow, B.W.; Robertson, I.M.; Jouiad, M.; Lassila, D.H.; Lee, T.C.; Birnbaum, H.K. |
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Observation of dislocation dynamics in the electron microscope |
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Journal Article |
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2001 |
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Materials Science And Engineering A |
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Mater. Sci. Eng. A |
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309-310 |
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445-450 |
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Deformation experiments performed in situ in the transmission electron microscope have led to an increased understanding of dislocation dynamics. To illustrate the capability of this technique two examples will be presented. In the first example, the processes of work hardening in Mo at room temperature will be presented. These studies have improved our understanding of dislocation mobility, dislocation generation, and dislocation-obstacle interactions. Zn the second example, the interaction of matrix dislocations with grain boundaries will be described. From such studies predictive criteria for slip transfer through grain boundaries have been developed. |
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0921-5093 |
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WOS:000169044600089 |
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NU @ m-krug @ |
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10533 |
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