2025-01-12
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PROCESSING AND PROPERTIES OF FE-10AL-4CR-4Y2O3 OXIDE DISPERSION STRENGTHENED (ODS) ALLOY CONSOLIDATED BY HOT ROTARY SWAGING
Krátká, L. ; Benč, Marek
This study deals with new generation of ODS alloys strengthened with a high-volume fraction of Y-nanooxides of 4 %. The ODS alloy is produced using powder metallurgy consisting of mechanical alloying of input powders followed by hot consolidation of canned powder using rotary swaging technology and secondary recrystallization to provoke coarse-grained microstructure. We focus on the microstructure characterization after individual processing steps and measurement of mechanical properties after consolidation and after secondary recrystallization at room temperature and 1100 degrees C. The mechanical properties of the studied ODS alloy are compared with those of a conventionally produced alloy as INCONEL718.
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2025-01-12
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ENHANCING PERFORMANCE OF ADDITIVELY MANUFACTURED AISI 316L BY ROTARY SWAGING
Benč, Marek ; Dvořák, K. ; Dvořák, Jiří ; Jakůbek, Zdeněk ; Pagáč, M.
This work deals with the study of structure and physical properties of 316 L austenitic stainless steel prepared by additive manufacturing and subsequently processed by the technology of rotary swaging. The semi-finished products were printed on a Renishaw 3D printing machine using the SLM (Selective Laser Melting) method, during which the metal powder is gradually sintered via cladding of individual layers using a powerful laser. Subsequently, room temperature rotary swaging was applied to enhance the structure and properties of the SLM- manufactured semi-product. The structural analyses showed that the swaging process imparted significant refinement of the average grain size, which decreased down to approx. 1.3 mu m (measured as the maximum feret diameter). As regards the physical properties, the density of the as-printed, as well as swaged, samples was measured using a pycnometer. As a result of forming, better material properties, such as increased density and improved hardness, were achieved. To confirm the advantages of the proposed approach consisting of a combination of 3D printing and deformation processing, all the results were compared with those acquired for an identical stainless steel prepared by conventional casting.
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2025-01-12
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EVOLUTION OF MICROSTRUCTURE OF MAGNESIUM MATERIALS PREPARED BY SPS USING VARIOUS COMPACTING PRESSURES
Brescher, R. ; Hasoňová, M. ; Březina, M. ; Fintová, Stanislava ; Doležal, P. ; Wasserbauer, J.
Compacting pressure applied during the SPS method varies in the literature. This study evaluates the influence of the applied compacting pressure on the microstructure and porosity of sintered materials. Using spark plasma sintering (SPS), cold compacted magnesium powder (green compacts) was sintered to bulk magnesium materials. The green magnesium compacts were prepared at room temperature using 100 MPa of uniaxial pressure, which was applied for 60 s. Using SPS, the green compacts sintering was carried out at 400 degrees C for 10 min. Various compacting pressures were applied during sintering: 20, 40, 60, 80 and 100 MPa to analyse the influence of the pressure. The resulting microstructure and porosity strongly depended on the compacting pressure applied during SPS. An increase of the compacting pressure was shown to be beneficial for material homogeneity, while this effect was pronounced up to 60 MPa, and only a slight effect on the material porosity was observed above this pressure.
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2025-01-12
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EFFECT OF THERMOMECHANICAL TREATMENT ON STRUCTURAL PHENOMENA AND ELECTROCONDUCTIVITY IN COPPER CONDUCTORS
Kunčická, Lenka ; Kačor, P. ; Dvořák, Jiří ; Jakůbek, Zdeněk
Despite its relatively high cost, copper is still the most popular electroconductive material. Its electroconductivity can be affected via structure modifications introduced by shear mixing, i.e. deformation processing, and/or thermomechanical treatment. Being an industrially applicable method of intensive plastic deformation, advantageously used to impart shear mixing, rotary swaging is favourable for production of long electroconductive wires. This study is focused on assessment of the effects of thermomechanical treatment on structural phenomena within copper conductors, the treatment consisted of room temperature rotary swaging and subsequent annealing. The results showed that the deformation ratio introduced via swaging was sufficient to impart homogenization of structure as the differences between the grain sizes and texture orientations within the peripheral and axial regions of the conductor were minimal. On the other hand, the swaged and annealed conductor featured slight inhomogeneity between the peripheral and axial regions, especially as regards structure regeneration and the occurrence of twinning, which was more pronounced in the axial region of the thermomechanically processed conductor (the volume fraction of <111> 60 degrees twin boundaries was 60 % within this sample region). Interestingly, the electroconductivity was higher than 100 % IACS (International Annealed Copper Standard) for the swaged conductor, and even increased up to 104.4 % IACS for the annealed conductor due to the structure modifications imparted by the applied heat treatment.
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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
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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
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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
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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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