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Control of intergranular oxidation by thermal treatment
Rothová, Věra ; Buršík, Jiří ; Svoboda, Milan
The effect of pre-annealing at 800 °C in argon atmosphere on high temperature corrosion at 1050 °C in air was studied on two high purity nickel grades and compared to a commercial purity nickel. Moreover, the influence of fabrication was analyzed in the case of cast and cold-rolled Puratronic® nickel samples. The mutual grain orientation was measured by means of electron backscatter diffraction and grain boundaries were characterized in terms of the coincidence site lattice model. The scanning electron microscope characterization of cross sections of all the oxidized samples has been performed and compared with the literature. The influence of purity and fabrication on the high temperature oxygen ingress in nickel was discussed in terms of grain boundary character distribution.
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The effect of annealing conditions on grain growth an microstructure in nickel
Rothová, Věra ; Svoboda, Milan ; Buršík, Jiří
In this paper, the influence of processing conditions (annealing atmosphere and temperature) on grain growth and microstructure evolution in nickel of two purity grades (99.5% and 99.9945%) was investigated. As regards pure nickel, the kinetic and thermodynamic parameters describing grain growth and the resulting evolution of twins during annealing in argon at 600–1100 °C has been studied and compared with the literature data. By the help of cross-sections of commercial purity nickel after annealing in air and/or argon, the effect of environment on grain growth was explained in relation to the depth of internal oxidation zone.
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Fatigue life and fatigue fracture of nickel-based superalloy Inconel 792-5A at room and at elevated temperatures
Šmíd, Miroslav ; Obrtlík, Karel ; Petrenec, Martin ; Polák, Jaroslav ; Hrbáček, K.
The aim of the present work is to study the effect of temperature on the fatigue life and fracture in cast polycrystalline nickel base superalloy Inconel 792-5A. Surface relief and fracture surface observations help to elucidate fatigue damage mechanism in the material used to produce the most critical component of gas turbines. Fatigue live curves can by approximated by the Manson-Coffin and Basquin law. Special attention was paid to the cyclic strain localisation on the specimen surface. Specimens strained with different strain amplitudes were used for fractographic investigation at each temperature. Both, the surface relief and the fracture surface observations, provide data on fatigue crack initiation. Detailed study of fracture surface topography was performed at all temperatures and different strain amplitudes and typical morphologies are documented. Fatigue damage mechanisms and crack path are discussed in relation to temperature, strain amplitude and crack lenght.
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Fatigue properties of Eurofer steel developed for fusion application
Kuběna, Ivo ; Kruml, Tomáš ; Hutař, Pavel ; Náhlík, Luboš ; Seitl, Stanislav ; Polák, Jaroslav
In this study fatigue properties of Eurofer 97 steel in room temperatures were measured. Fatigue parameters of the cyclic stress - strain curve and fatigue life curves (Coffin-Manson curve and derived Wöhler curve) were evaluated. Major attention was given to the measurement of kinetics of fatigue crack growth by two different methods. The initiation sites of fatigue cracks and short crack growth were observed and measured on cylindrical specimens with shallow notch. These cracks had a length from 20 micrometers to 1 mm. Kinetics of growth of long cracks with the length 15-30 mm was measured on CT specimens. It was found that results obtained by the both methods are in a good agreement if the J-integral is used. It was possible to determine the threshold values of J-integral and stress intensity factor and to calculate the Paris law parameters.
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Analýza přerozdělení prvků feritických ocelí s Ni povlakem pro technologie roztavených solí
Král, Lubomír ; Čermák, Jiří ; Matal, O. ; Šimo, T. ; Nesvadba, L. ; Jílek, M.
Changes in structure and chemical composition of Ni-coated ferritic steel ČSN 411523 are studied in the present paper. The Ni-coated material is perspective for applications in molten salts technologies. The samples were subjected to corrosion in molten mixture 60 mol. % LiF + 40 mol. % NaF at temperature 953 K, the duration exposition was 100, 300 and 1000 h. Experiments were carried out in a quasidynamic regime simulating the flow of the cooling media (the mixture of molten salts) in the pipeline system. The change of chemical composition in the vicinity of interface between the Ni layer and steel substrate was measured by SEM.
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Objemová kovová skla na bázi železa - optimalizace odlévání
Stloukal, Ivo ; Král, Lubomír ; Čermák, Jiří
In this paper, the iron-based alloy was studied that is perspective for preparation of bulk metallic glass. The nominal composition of investigated material is given by the formula Fe.sub.56./sub.Co.sub.7./sub.Zr.sub.10./sub.Mo.sub.5./sub.W.sub.2./sub. B.sub.15./sub.. Two casting techniques were applied: (i) conventional casting into a copper mould in the induction furnace and (ii) casting in the arc furnace in the copper mould. In the first case, the diameter of the ingot was about 11 mm. In the second case, the special two-parts copper moulds differing in diameters of the casting inlet hole (3 and 1 mm, respectively) were used. The microstructure of alloys prepared by both techniques was studied using the light optical microscopy, SEM (Scanning Electron Microscopy) and XRD (X-ray diffraction).
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