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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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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 Fe91-yMo8Cu1By – srovnání vlivu difuzivit Fe a Mo
Čermák, Jiří ; Stloukal, Ivo
Partly crystallized alloys Fe91-yMo8Cu1By belong to a NANOPERM-type family with excellent soft-magnetic behavior. Molybdenum, as an alloying element, causes that the Currie temperature of both amorphous and nano-crystallized form of the alloys is close to the room temperature, which opens possibilities to numerous applications. In the present work, structure changes of three chosen alloys (y = 12, 15, 17) are investigated after several temperature treatments by TEM, XRD and DSC and diffusivity of the principal metallic components is measured in the temperature interval 548 – 773 K. It was found that bulk diffusion coefficients of Fe and Mo in relaxed amorphous state are about the same, but grain boundary diffusivity of Fe is much higher than that of Mo. Such a difference in grain boundary diffusivity may act as structure stabilizing factor.
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Heterodifúze 65Zn v binárních slitinách Mg - x Al av komerční slitině AZ91
Čermák, Jiří ; Stloukal, Ivo
Bulk diffusion coefficient of Zn, D, in Mg – x Al model alloys (x = 0, 1.8, 3.9 and 9 at. %), in commercial alloy AZ91 and in intermetallic compound Mg17Al12 intermetallic was measured by residual activity and serial sectioning methods. Composition dependence of D was obtained, that shows a slight increase of D with increasing Al concentration. Measurements were done at several diffusion temperatures, which enabled to evaluate the pre-exponential factor and the activation enthalpy of Zn diffusion.
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Difúze 65Zn ve dvoufázové eutektické slitině Mg - 33 wt.% Al
Čermák, Jiří ; Stloukal, Ivo
Diffusion of zinc in a two-phase eutectic alloy Mg – 33 wt.% Al and in its components, Mg – Al solid solution and in the intermetallic compound Mg17Al12, was studied. The measurement of Zn diffusion coefficient was carried out by radiotracer technique in temperature interval 498 – 848 K. Zinc is believed to simulate the migration behavior of magnesium. It was observed that the interphase boundaries do not act as short-circuit paths. The study of the stability of the eutectic structure enabled to estimate the mean specific energy of the (Mg)/ Mg17A12 phase interface.
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Difúze 99Mo ve teplně zpracované slitině Fe76Mo8Cu1B15
Čermák, Jiří ; Stloukal, Ivo
Ion beam sputtering by Ar+ ions was used to investigate 99Mo tracer diffusion in Fe76Mo8Cu1B15 alloy in the temperature range 548 – 648 K. The experimental samples were prepared from ribbons of Fe76Mo8Cu1B15 alloy in as quenched state q, and after pre-annealing at 683 K for 1 h (state a1) and at 743 K for 1 h (state a2). The penetration profiles were obtained using serial sectioning method and consist of two parts suggesting that two different diffusion paths are operating. The Mo short-circuit diffusivity P was evaluated using both LeClaire’s analysis and Divinski’s theory derived for transition type-A/B regime in coarse-grained materials.
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Difúzní studie Fe a Mo ve slitině Fe76Mo8B15Cu1
Čermák, Jiří ; Stloukal, Ivo
59Fe and 99Mo tracer diffusion in Fe76Mo8B15Cu1 alloy was studied using serial sectioning method in the temperature range 527 – 649 K. The ribbon-like samples were annealed at 695 K for 1 and 5 hours before the diffusion experiments; the volume fraction of crystalline phase was checked by the Mössbauer spectroscopy. Concentration profiles obtained by sputtering by Ar+ ions in a glow discharge show two distinct branches suggesting that two diffusion paths are operating.
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