2024-12-22
00:01 |
Microstructural Processes in Thermal Creep of Zirconium Nuclear Fuel Cladding Tubes
Král, Petr ; Kuchařová, Květa ; Kvapilová, Marie ; Dvořák, Jiří ; Krejčí, J. ; Sklenička, Václav
The origin of the thermal creep of zirconium cladding tubes in all light water reactors is still the subject of deep confusion and intricate controversies. The reason for this inconvenient situation is\nobviously that microstructural processes in thermal creep remain poorly understood and this is due to the relatively small number of studies that have been carried out. In this study uniaxial creep tests in tension of zirconium alloy cladding tubes in the as-received and pre-hydrided states are followed by metallographic analysis of the as-received and crept specimens by light microscopy and SEM to explain the observed high-temperature creep behavior of the tubes.
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2024-12-22
00:01 |
VLIV VRUBU NA CREEPOVOU ODOLNOST NIZKOLEGOVANÉ CR-\nMO-V OCELI (ČSN 15 128)
Dvořák, Jiří ; Kvapilová, Marie ; Král, Petr ; Kuchařová, Květa ; Ohanková, M. ; Sklenička, Václav
Pro zvýšení spolehlivosti a přesnější predikci životnosti vysokoteplotních komponent je ne-\nzbytné porozumět chování a vlivu defektů, které se v creepově odolných materiálech vyskytují\nv důsledku přítomnosti lokálních koncentrátorů napětí-vrubů. Koncentrace víceosého napětí,\nvzniklá přítomností vrubu, ovlivňuje creepové vlastnosti konstrukčního materiálu. Tato studie\nje zaměřena na výzkum vlivu V-vrubu na creepovou odolnost degradované parovodní trubky\nz nízkolegované 0.5%Cr-0.5%Mo-0.3%V oceli (ČSN 15 128) po dlouhodobém provozním na-\nmáhání. Pro porovnání creepových vlastností byly provedeny doplňující creepové zkoušky i na\nvzorcích výchozího stavu parovodní trubky. Creepové zkoušky byly realizovány na hladkých\nvzorcích i vzorcích s V-vrubem při teplotě 550 °C v širokém intervalu aplikovaných tahových\nnapětí. Za zvolených experimentálních podmínek byl prokázán zpevňující vliv vrubu, který lze\npřisuzovat lokálnímu víceosému namáhání, které vedlo k lokálnímu rozložení napětí během\ncreepové expozice.
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2024-12-22
00:01 |
VLIV VODÍKU NA CREEPOVOU ODOLNOST ZIRKONIOVÉHO\nPOKRYTÍ JADERNÉHO PALIVA PŘI PROVOZNÍ TEPLOTĚ\nREAKTORU
Sklenička, Václav ; Kuchařová, Květa ; Král, Petr ; Kvapilová, Marie ; Dvořák, Jiří ; Vrtílková, V. ; Krejčí, J.
Příspěvek je zaměřen na výzkum vlivu vodíku na creepovou odolnost zirkoniové slitiny\nZr1%Nb povlakových tyčí jaderného paliva, určených pro vodou chlazené reaktory typu\nVVER. Segmenty vyřezané z povlakových tyčí byly použity jako tubulární creepové vzorky.\nČást creepových vzorků byla podrobena předhydridaci na úroveň koncentrace vodíku v rozmezí\n371–656 wppm H. Komparativní creepové zkoušky při konstantním napětí byly provedeny při\nteplotě 350 °C a tahovém napětí 150–225 MPa na vzorcích ve výchozím stavu a po modelové\nhydridaci. Bylo zjištěno, že koncentrace cH ≤ 400 wppm vede ke zrychlení creepové deformace,\na tudíž k degradaci creepové odolnosti. Naopak, vyšší koncentrace vodíku vede ke snížení rych-\nlosti creepové deformace a zvýšení creepové odolnosti. Rozdílný vliv H na creepové chování\nbyl připsán přítomnosti atomárního vodíku a vodíku ve formě hydridů zirkonia.
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2024-07-27
00:02 |
QUANTUM-MECHANICAL STUDY OF INTERNAL STRUCTURAL TRANSFORMATIONS IN Pb-SUPERSATURATED Pb-Sn ALLOYS
Friák, Martin ; Čípek, Petr ; Pavlů, J. ; Roupcová, Pavla ; Miháliková, Ivana ; Msallamová, Š. ; Michalcová, A.
Motivated by a decades-long controversy related to the crystal structure of Pb-supersaturated solid solutions of Pb in Sn, we have performed a quantum-mechanical study of these materials. Focusing on both body-centred-tetragonal beta-Sn and simple-hexagonal gamma-Sn structures, we have computed properties of two alloys with the chemical composition Pb5Sn11, i.e. 31.25 at. % Pb, which is close to the composition of the experimentally found alloy (30 at. % Pb). The 16-atom computational supercells were designed as multiples of the elemental beta- and gamma-Sn unit cells, where the Pb atoms were distributed according to the special quasi-random structure (SQS) concept. Full structural relaxations of both beta- and gamma-phase-based alloys resulted in very significant re-arrangements into structures which do not exhibit any apparent structural features typical for the original alloys, and are, therefore, difficult to classify. The formation energies of the beta- and gamma-phase-originating equilibrium phases are 50 meV/atom and 53 meV/atom, respectively. Therefore, they are not stable with respect to the decomposition into the elemental lead and tin. Moreover, our calculations of elastic constants of both phases revealed that they are close to mechanical instability. Our results indicate that the studied Pb-supersaturated Pb-Sn solid solutions may be prone to structural instability, transformations into different phases and decomposition. Our findings may contribute into the identification of the reason why the subsequent experimental studies did not reproduce the initial published data.
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2024-07-27
00:02 |
QUANTUM-COMPUTING STUDY OF THE ELECTRONIC STRUCTURE OF CRYSTALS: THE CASE STUDY OF SI
Ďuriška, Michal ; Miháliková, Ivana ; Friák, Martin
Quantum computing is newly emerging information-processing technology which is foreseen to be exponentially faster than classical supercomputers. Current quantum processors are nevertheless very limited in their availability and performance and many important software tools for them do not exist yet. Therefore, various systems are studied by simulating the run of quantum computers. Building upon our previous experience with quantum computing of small molecular systems (see I. Mihalikova et al., Molecules 27 (2022) 597, and I. Mihalikova et al., Nanomaterials 2022, 12, 243), we have recently focused on computing electronic structure of periodic crystalline materials. Being inspired by the work of Cerasoli et al. (Phys. Chem. Chem. Phys., 2020, 22, 21816), we have used hybrid variational quantum eigensolver (VQE) algorithm, which combined classical and quantum information processing. Employing tight-binding type of crystal description, we present our results for crystalline diamond-structure silicon. In particular, we focus on the states along the lowest occupied band within the electronic structure of Si and compare the results with values obtained by classical means. While we demonstrate an excellence agreement between classical and quantum-computed results in most of our calculations, we further critically check the sensitivity of our results with respect to computational set-up in our quantum-computing study. A few results were obtained also using quantum processors provided by the IBM.
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2024-07-27
00:02 |
EFFECT OF STEEL COMPOSITION ON ITS BEHAVIOUR IN THE LIQUID LEAD ENVIRONMENT
Pazderova, M. ; Hojná, A. ; Vít, J. ; Hadraba, Hynek ; Čižek, J.
Ferritic-martensitic Eurofer-97 and oxide dispersion strengthened (ODS) Eurofer steels are potential candidates for structural applications in advanced nuclear reactors. Influence of scandium, yttrium, and aluminum addition was studied at 600 degrees C using 10-6 wt.% oxygen concentration. Microstructure and corrosion behaviour was evaluated after 500 h and 1000 h of exposure to liquid lead. Microscopical investigation identified oxidation, solution- based attack, and Pb penetration into the material. Addition of scandium and aluminum changed the mechanism of corrosion attack. Eurofer-97 was partially protected by outer oxide and inner oxidation and Pb penetration was found. In contrast ODS-Eurofer steels after 1000 h of exposure showed mainly inner oxidation and SBA including Pb penetration into the steel. The inner oxidation consisted of Pb+Cr-O and Cr-O+Al-O layers mixture. Degradation of ODS steel was significantly lower than Eurofer-97. It seems that the inner oxidation layer beneath the surface did not prevent the Pb penetration but protected the surface from dissolution.
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2024-07-27
00:02 |
MINOR PHASES IN TIN-RICH HISTORICAL MATERIALS
Michalcová, A. ; Msallamová, Š. ; Fink, D. ; Friák, Martin
The historical organ pipes used to be manufactured from tin and tin-lead alloys. The tin-rich organ pipes usually contained copper as alloying elements, which make them similar to modern lead free soldering materials. The historical organ pipe materials can be used as model materials for natural ageing of soldering materials. Tin pest is a term for modification from white tin to grey tin, which leads to degradation of tin or tin-rich alloys. The influence of individual alloying elements has not been reliably described, yet. Not only on the concentration of the alloying element, but also the distribution may play the important role. In dependence on heat-treatment, the Cu can be in the Sn matrix present in these forms: i) as large intermetallic particles after casting (Cu6Sn5), ii) as solid solution after homogenization annealing and iii) as fine precipitates after ageing. The microstructure of the real historical organ-pipes material was studied and it was proven that contradictionary to the equilibrium phase diagram the Cu enriched was observed.
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2024-07-27
00:02 |
EFFECT OF OXIDE DISPERSION ON ELECTRIC CONDUCTIVITY OF ROTARY SWAGED POWDER-BASED COPPER COMPOSITES
Kunčická, Lenka ; Benč, Marek ; Kačor, P. ; Marek, M.
Copper is a very popular electro-conductive material, however, the mechanical properties of pure Cu are low. They can be typically improved by (micro)alloying, or via structure modifications introduced by optimized deformation and thermomechanical treatments. Designing a Cu-based composite, possibly strengthened by a dispersion of fine oxides, is another way how to favourably improve the strength properties of Cu. In this study, we performed mechanical alloying of a Cu powder with a powder of Al2O3 oxide, which is known to have strengthening effects on metallic materials. After mixing, we sealed the powder mixture into evacuated tubular Cu containers (i.e. cans). As for the consolidation procedure, we applied direct consolidation of the canned powders via the intensive plastic deformation method of rotary swaging, performed under warm conditions. Subsequently, we subjected the swaged conductors to measurements of electric conductivity and detailed structure observations. The results revealed that the applied swaging ratio was sufficient to fully consolidate the canned powders as the final conductor was unrecognizable from a cast alloy from the viewpoints of visual and structure assessment. In other words, the structure did not exhibit any voids or remnants of unconsolidated powder particles. The observed fine grains with homogeneous dispersion of Al2O3 oxide particles provided improvement of the mechanical properties, as proven by microhardness measurements. Moreover, the electric properties remained favourable.
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2024-06-30
06:40 |
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2024-04-27
00:01 |
Nanoparticels from brake pads wear
Švábenská, Eva ; Roupcová, Pavla ; Friák, Martin ; Schneeweiss, Oldřich
Exposure to particulate air pollution has been associated with a variety of health problems. One of the main\nsources of metal-rich airborne particulate pollution in roadside environments are brake-wear emissions. The \nscanning electron microscopy (SEM) and transmission electron microscopy (TEM), Mössbauer spectroscopy \n(MS), X-ray powder diffraction (XRD) was used to a make quantitative evaluation of wear particles in two \nsamples. Sizes, morphologies, oxidation state, and trace element compositions of wear particles were\ninvestigated using combination of several methods revealed high concentrations of Fe species and phases, \noften associated with carbonaceous material. SEM and TEM observations show that brake wear particles with \na size of tens to hundreds of nm mainly form particle agglomerates. However, ultrafine (<100 nm) particles are \nlikely to pose a health threat after inhalation and/or ingestion.
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