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Interakce mezi Ti-Al-Nb taveninou a Y2O3 kelímky
Barták, Tomáš ; Dlouhý, Antonín ; Dočekalová, Kateřina ; Zemčík, L.
The present paper focuses on interactions between intermetallic melts (Ti-46Al-7Nb-0.7Cr-0.1Si-0.2Ni alloy (at%)) and ceramic crucibles based on the Y2O3 refractory. Different levels of superheat and exposure time are taken into account. Vacuum induction melting (VIM) experiments were performed using the vacuum furnace BALZERS VSG 02. The controlled argon atmosphere inside the furnace volume was kept at the pressure level of 0.133 bar during the melting experiments. The reactions at the melt - crucible interface were studied by means of scanning electron microscopy (SEM) equipped with the energy dispersive x-ray analyzer (EDX). There has been clear benefit when a common refractory like alumina has been replaced by yttria. However, the results obtained in this study show, that the long - term exposure at melting temperatures above 1650°C lead to notable reactions at the interface. We discuss the stability of the melt - ceramic system using principles of thermodynamic equilibrium.
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Low cycle fatigue of ferritic ductile cast iron with alloying nickel
Tesařová, H. ; Petrenec, Martin ; Pacal, B.
Total strain controlled tests have been performed on cylindrical specimens of ductile cast iron with aim to assess of the fatigue resistance. Cyclic hardening, cyclic stress-strain and fatigue life curves were obtained. The microstructure is documented using light microscope. Fracture surface was studied using scanning electron microscopy. Manson-Coffin and Basquin laws can reasonably approximate the fatigue life data. Fatigue crack initiation close to the surface is documented.
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Low cycle fatigue on Inconel 713L and Inconel 792-5A superalloys at 500 A 700 °C
Petrenec, Martin ; Obrtlík, Karel ; Polák, Jaroslav ; Hrbáček, K. ; Kruml, Tomáš
Cylindrical specimens of cast polycrystalline nickel base superalloys Inconel 713LC and 792-5A were cyclically strained under total strain control at500°C and at700°C.Structural characteristics and morphology of gama´ precipitates of both materials are documented. Dislocations structures were studied using transmission electron microscopy using technique of oriented foils in selected specimens cyclically strained up to failure. Cyclic hardening/softening curves, cyclic stress-strain curves, and fatigue life curves were obtained for both temperatures. Cyclic hardening/softening curves depend both on temperature and plastic strain amplitude. The cyclic stress-strain curves can be approximated by power law. Experimental points of fatigue life curves satisfy the Manson-Coffin and Basquin law. Stress-strain response and fatigue life characteristics are compared at both temperatures and discussed in relative to structural parameters and to dislocation structures of superalloys studied.
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Low Strain Creep of ex-service 0.5CrMoV Steel
Kloc, Luboš
Helicoid spring creep testing technique with high strain sensitivity was applied on specimens of low-alloy steel after 197 thousands hours in service. The creep testing conditions were selected to be close to that of the service, that is 560 °C and 35MPa. The ex-service specimens creep much faster than the unused one and an anisotropy in creep properties was also observed. The method is capable to provide some additional information for the residual creep life assessment, but interpretation of the results is quite difficult. The large volume of the material needed for testing is also considerable disadvantage.
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Jednoduchá metoda pro difúzní měření využívající zbytkové aktivity
Rothová, Věra
A simple and sensitive technique using the liquid scintillation (LS) counter has been developed which is based on a solid scintillator in place of the commonly used LS cocktail. As a test case, the method was applied to the successful determination of the Ni-63 self-diffusion profile in commercial purity nickel by means of the Gruzin's residual activity technique.
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Mechanismus difúze 88Y ve slitině QE22
Čermák, Jiří ; Stloukal, Ivo
Diffusion of radioisotope 88Y was studied in magnesium-based alloy QE22 (nominal composition: Mg – 2 RE – 2.5 Ag – 0.6 Zr in wt. %, RE – rare earth metal) in temperature interval ranging from 648 K to 728 K. Diffusion behavior of the chosen tracer, which is suitable for diffusion measurements, simulates the typical migration characteristics of mischmetal components in general. Mixture of RE’s used for alloying contains Ce and Nd as principal elements and it is added in QE22 to promote the creep resistance. It was found that yttrium diffuses along dislocations that act as paths of rapid diffusion. Diffusivity of 88Y along dislocations, a2sDd, was estimated.
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Kinetika vodíku v Mg2Ni a v hydrogenovaném eutektiku Mg-Mg2Ni
Čermák, Jiří ; Král, Lubomír ; Stloukal, Ivo
Time dependence of total amount of hydrogen desorbed from hydrogen-charged Mg and eutectic Mg-Mg2Ni (23.5 wt. % Ni) alloy was measured at temperatures from interval 552 – 723 K. Experiments were carried out well below the equilibrium pressure, where these hydrides – perspective as solid hydrogen storage media – are unstable and the desorption process is controlled mainly by diffusion of hydrogen in respective hydride (MgH2 and/or Mg2NiH4). Hydrogen diffusion coefficients were evaluated from desorption curves and hydrogen diffusion coefficient along interphase boundary MgH2/Mg2NiH4 was estimated from results obtained with the eutectic alloy.
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Strukturní změny ve slitinách Mg-Ni po absorpci a desorpci vodíku
Král, Lubomír ; Čermák, Jiří
This paper deals with changes of structure in Mg-Ni alloys after absorption and desorption of hydrogen. Experimental materials were prepared by two techniques – by casting and by ball milling and subsequent compacting to pellets. These materials were hydrogen-charged at elevated temperature and pressure. Materials were studied using the SEM Jeol JSM 6460 equipped with EDS/WDS analyzers. Formation of rectangular particles of MgNi2, nucleation of MgH2 at grain boundaries, and changes of Mg2Ni were observed. The so-called activation of hydrogen storage alloy is most likely due to fine particles that appear after the first hydrogen charging.
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