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Park, Kyung-Tae; Lee, Hang-Jae; Lee, Chong Soo; Nam, Won Jong; Shin, Dong Hyuk |
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Enhancement of high strain rate superplastic elongation of a modified 5154 Al by subsequent rolling after equal channel angular pressing |
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2004 |
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Abstract  |
Scripta Materialia |
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Scripta Mater. |
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51 |
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6 |
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Summary Language |
479-483 |
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Aluminum alloy; Superplasticity; Equal channel angular pressing; Rolling |
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Abbreviated Series Title |
Subsequent rolling after equal channel angular pressing (ECAP) resulted in a considerable enhancement of the high strain rate superplastic elongation of a modified 5154 Al alloy, compared to that of the alloy subjected to the identical ECAP strain without rolling. The mechanical data revealed that the deformation of the former was governed by grain boundary sliding but that of the latter was dominated by viscous glide. |
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NU @ karnesky @ |
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586 |
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Park, J.H.; Lee, Y.S.; Nam, W.J.; Park, K.T. |
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Comparison of compressive deformation of ultrafine-grained 5083 Al alloy at 77 and 298 K |
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Journal Article |
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2005 |
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Metallurgical And Materials Transactions A-Physical Metallurgy And Materials Science |
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Metall. Mater. Trans. A-Phys. Metall. Mater. Sci. |
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36a |
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5 |
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1365-1368 |
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The compression behaviors of well-annealed coarse-grained (CG) and ultrafine-grained (UFG) 5083 Al alloys at 77 and 298 K were compared. For the CG alloy, stage II and III strain hardening were dominant at 77 and 298 K, respectively, depending on the completeness of dislocation cell formation. The UFG alloy exhibited the elastic-near perfectly plastic behavior without distinctive dislocation cell formation at both temperatures. For both alloys, the flow stress at 77 K was much higher than that at 298 K. |
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Hanbat Natl Univ, Div Adv Mat Sci & Engn, Taejon 305719, South Korea, Email: ktpark@hanbat.ac.kr |
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Minerals Metals Materials Soc |
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English |
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1073-5623 |
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ISI:000228797500029 |
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NU @ karnesky @ |
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10027 |
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Mao, Zugang; Kim, Yeong-Cheol; Lee, Hi-Deok; Adusumilli, Praneet; Seidman, David N. |
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NiSi crystal structure, site preference, and partitioning behavior of palladium in NiSi(Pd)/Si(100) thin films: Experiments and calculations |
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2011 |
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Applied Physics Letters |
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99 |
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1 |
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013106 |
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ab initio calculations; crystal structure; metallic thin films; nickel alloys; palladium alloys; silicon alloys; tomography; X-ray diffraction |
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The crystal structure of a NiSi thin-film on a Si substrate and Pd site-substitution in NiSi and the partitioning behavior of Pd for NiSi(Pd)/Si(100) are investigated by x-ray diffraction (XRD), first-principles calculations, and atom-probe tomography (APT). The NiSi layer is a distorted orthorhombic structure from XRD patterns via experiments and calculations. We find that Pd has a strong driving force, 0.72 eV atom−1, for partitioning from Si into the orthorhombic NiSi layer. The calculated substitutional energies of Pd in NiSi indicate that Pd has a strong preference for Ni sublattice-sites, which is in agreement with concentration profiles determined by APT. |
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Aip |
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NU @ karnesky @ ref10.1063/1.3606536 |
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11169 |
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Veerababu, R.; Balamuralikrishnan, R.; Muraleedharan, K.; Srinivas, M. |
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Three-dimensional atom probe investigation of microstructural evolution during tempering of an ultra-high-strength high-toughness steel |
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Journal Article |
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2008 |
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Metallurgical And Materials Transactions A-Physical Metallurgy And Materials Science |
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Metall. Mater. Trans. A-Phys. Metall. Mater. Sci. |
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39a |
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1486-1495 |
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The evaluation of the tempering response of an ultra-high-strength, high-toughness (UHSHT) steel revealed that samples austenitized at 900 degrees C and tempered for 4 and 8 hours at 485 degrees C had similar yield strengths but a similar to 50 pct increase in fracture toughness for the 8-hour temper. The results of our investigations of microstructural origins of this difference, using the nanometric scale resolution of the three-dimensional atom probe (3DAP) suggest that nanoscale strengthening precipitates, essentially carbides and intermetallic clusters (containing primarily Cr and Mo atoms), are present in both samples. The chemical compositions of the particles in the two samples were found to be similar, but clear evidence of differences in physical attributes of the precipitates, such as particle size, morphology, and interparticle spacing, are seen. |
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Def Met Res Lab, Hyderabad 500058, Andhra Pradesh, India, Email: muraleek@hotmail.com |
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Springer |
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English |
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1073-5623 |
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ISI:000256081500004 |
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NU @ m-krug @ |
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10377 |
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Seol, J.; Lim, N.; Lee, B.; Renaud, L.; Park, C. |
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Atom probe tomography and nano secondary ion mass spectroscopy investigation of the segregation of boron at austenite grain boundaries in 0.5 wt.% carbon steels |
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Journal Article |
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2011 |
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Metals and Materials International |
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17 |
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3 |
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413-416 |
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Metallic Materials |
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The grain boundary segregation of boron atoms in high strength low alloy steels containing 50 ppm boron was accomplished using atom probe tomography (APT) and nano-beam secondary ion mass spectroscopy (SIMS). The formation of boro-carbides under an excessive addition of boron to the steels was identified through the SIMS and TEM. The APT was performed in order to evaluate the composition of the alloying elements, such as, boron and carbon, segregated at prior austenite grain boundaries. The boron contents at the prior austenite grain boundaries were approximately 1.7 ± 0.2 at.%, which was approximately 70 times more than the amount of boron added to the steels. |
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The Korean Institute of Metals and Materials, co-published with Springer Netherlands |
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1598-9623 |
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NU @ karnesky @ |
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11171 |
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Suh,Dong-Woo; Lee, Sang-Yong; Lee, Kyong-Hwan; Lim, Su-Keun; Oh, Kyu Hwan |
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Microstructural evolution of Al–Zn–Mg–Cu–(Sc) alloy during hot extrusion and heat treatments |
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Journal Article |
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2004 |
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Journal of Materials Processing Technology |
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155-156 |
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1330-1336 |
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Scandium; Microstructure; Recovery; Recrystallization |
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The microstructural evolution during hot extrusion and post heat treatment was investigated for two kind of Al–Zn–Mg–Cu–(Sc) alloy and AA7075. The microstructure of as-extruded bar is mainly comprised of recovered structure for all alloys, however, different restoration processes are observed during post heat treatment. For AA7075 and S1, which contains 0.1% Sc with relatively higher Zn and Cu content than S2, recovery still proceeds during the heat treatment, while the recrystallization becomes main restoration process during the heat treatment for S2.
The differences in abnormal grain growth and hardening behavior between S1, AA7075 and S2 during the heat treatment are discussed in connection with the restoration processes and resultant microstructures. |
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NU @ karnesky @ |
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622 |
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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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Michler, Thorsten; Lee, Yongwon; Gangloff, Richard P.; Naumann, Joerg |
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Influence of macro segregation on hydrogen environment embrittlement of SUS 316L stainless steel |
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Journal Article |
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2009 |
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International Journal of Hydrogen Energy |
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34 |
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7 |
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3201-3209 |
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Hydrogen embrittlement; Austenitic stainless steel; Macro segregation; Nickel |
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The objective of this work is to identify microstructural variables that lead to the large scatter of the relative resistance of 316 grade stainless steels to hydrogen environment embrittlement. In slow displacement rate tensile testing, two almost identical (by nominal chemical composition) heats of SUS 316L austenitic stainless steel showed significantly different susceptibilities to HEE cracking. Upon straining, drawn bar showed a string-like duplex microstructure consisting of [alpha]'-martensite and [gamma]-austenite, whereas rolled plate exhibited a highly regular layered [alpha]'-[gamma] structure caused by measured gradients in local Ni content (9.5-13 wt%). Both martensite and austenite are intrinsically susceptible to HEE. However, due to Ni macro segregation and microstructural heterogeneity, fast H-diffusion in martensite layers supported a 10 times faster H-enhanced crack growth rate and thus reduced tensile reduction in area. Nickel segregation is thus a primary cause of the high degree of variability in H2 cracking resistance for different product forms of 316 stainless steel. |
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0360-3199 |
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NU @ karnesky @ |
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10957 |
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Lee, W.S.; Chen, T.H. |
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Effects of strain rate and temperature on dynamic mechanical behaviour and microstructural evolution in aluminium-scandium (Al-Sc) alloy |
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Journal Article |
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2008 |
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Materials Science and Technology |
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24 |
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10 |
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1271-1282 |
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AL-SC ALLOY; STRAIN RATE SENSITIVITY; ACTIVATION ENERGY; ADIABATIC SHEARING; DISLOCATION; AL3SC PRECIPITATES |
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The present study applies a compressive split Hopkinson bar to investigate the mechanical response, microstructural evolution and fracture characteristics of an aluminium-scandium (Al-Sc) alloy at temperatures ranging from − 100 to 300°C and strain rates of 1·2 × 103, 3·2×103 and 5·8 × 103 s−1. The relationship between the dynamic mechanical behaviour of the Al-Sc alloy and its microstructural characteristics is explored. The fracture features and microstructural evolution are observed using scanning and transmission electron microscopy techniques. The stress-strain relationships indicate that the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, but decrease with increasing temperature. Conversely, the activation volume and activation energy increase as the temperature increases or the strain rate decreases. Additionally, the fracture strain reduces with increasing strain rate and decreasing temperature. The Zerilli-Armstrong fcc constitutive model is used to describe the plastic deformation behaviour of the Al-Sc alloy, and the error between the predicted flow stress and the measured stress is found to be less than 5%. The fracture analysis results reveal that cracks initiate and propagate in the shear bands of the Al-Sc alloy specimens and are responsible for their ultimate failure. However, at room temperature, under a low strain rate of 1·2 × 103 s−1 and at a high experimental temperature of 300°C under all three tested strain rates, the specimens do not fracture, even under large strain deformations. Scanning electron microscopy observations show that the surfaces of the fractured specimens are characterised by transgranular dimpled features, which are indicative of ductile fracture. The depth and density of these dimples are significantly influenced by the strain rate and temperature. The transmission electron microscopy structural observations show the precipitation of Al3Sc particles in the matrix and at the grain boundaries. These particles suppress dislocation motion and result in a strengthening effect. The transmission electron microscopy analysis also reveals that the dislocation density increases, but the dislocation cell size decreases, with increasing strain rate for a constant level of strain. However, a higher temperature causes the dislocation density to decrease, thereby increasing the dislocation cell size. |
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NU @ m-krug @ |
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10531 |
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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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Journal Article |
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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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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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Asme |
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NU @ karnesky @ |
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10983 |
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