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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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Studium struktury a magnetismu FeCo při vysokých deformacích z prvních principů
Čák, Miroslav ; Legut, Dominik ; Šob, Mojmír
Total energies and magnetic moments of FeCo along the tetragonal deformation path are calculated using first-principles electronic structure methods. Total energies are displayed in a contour plot as a function of tetragonal distortion and volume; borderline between the ferromagnetic and nonmagnetic states is shown. The calculated energies may be used to predict the lattice parameters of FeCo thin films on various (001) substrates; here we study the FeCo film on the MgO(001) substrate. The calculated results are compared with available experimental data. The loss of magnetism of FeCo at low atomic volumes and large shape deformations is observed.
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Možné transformační dráhy spojující struktury C11b, C40 and C54 v MoSi2
Káňa, Tomáš ; Legut, Dominik ; Šob, Mojmír
We suggest three transformation paths between the ideal C11b , C40 and C54 structures of transition-metal disilicides. These three structures can be regarded as different stackings of identical planes of atoms. Each suggested transformation path consists in shifting these atomic planes in three directions. The shift of planes is described by one parameter p <0;1>. Along each path, we calculate the total energy of MoSi2 as a function of p. Our results confirm the structural order C11b → C40 →C54 in MoSi2. The C11b–C54 path exhibits the largest energy barrier, 2.5 eV/f.u (f.u. means the formula unit). The energy barrier of the C11b–C40 path is lower, 1.7 eV/f.u. and finally the energy barrier of the C40–C54 path is the lowest one, 1.4 eV/f.u.
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Multiscale design of advanced materials
Král, L. ; Million, Bořivoj
In this paper, the results of measurements of chemical diffusion of Mn in steel weldments are reported. Chemical concetnration of Mn an interval 0-15 wt.% Mn was varied. Alloys were casted in induction furnace under protective Ar atmosphere. Diffusion couples were annealed at 800-1100°C for 96-1.5 hours respectively. Measurement of Mn redistribution was done in a normal direction to welding interface using scanning electron microscope Philips SEM-505WDS equipped with Microspec WDX-2A. Diffusion coefficients of Mn were obtained by fitting experimental curves to the known analytical solution.
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Přístroj pro měření koncentračních profilů – Analýza výstupních dat
Čermák, Jiří ; Stloukal, Ivo
In this paper, a new modification of a commercial apparatus Edwards Coating system E306A is described that enables to perform diffusion measurements with radioactive tracers. The plan-parallel thin layers are removed by sputtering with Ar+ ions and the well defined fraction of the sputtered-off material is sequentially collected. The function of the apparatus is exemplified by the measurement of bulk diffusion coefficient of 65Zn in Fe40Ni40B20 alloy at T = 684 K.
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Difúze 71Ge a 68Ge v Mg a ve slitině Mg-2Al
Čermák, Jiří ; Eversheim, D. ; Rothová, Věra ; Stloukal, Ivo
Measurement of Ge diffusion coefficients in Mg and in Mg-1.8 wt.% Al alloy is presented in this work. Two techniques of Ge deposition and two annealing atmospheres (Ar and Ar + Cl2) were tested which might reveal possible influence of hold-up effect at the free surface on the diffusion behavior. The present results are compared with the literature data for volume diffusion of other impurities in Mg.
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Kombinovaný difúzní režim nízkorozpustné příměsi v polykrystalu – Modelový systém – Ge v Mg a ve slitině Mg-1,8 wt.% Al
Čermák, Jiří
Unusual diffusion regime observed in a case of extremely low-soluble element in Mg alloys was described. The low solubility of diffusant was found to affect significantly the transport properties in the range, where the volume diffusion usually operates. The proposed way of data evaluation enabled calculation of segregation factor of Ge in Mg and in alloy Mg – 1.8 wt. % Al. Temperature dependence of measured diffusion coefficient in grain boundary, Db, grain boundary diffusivity, P, and temperature dependence of calculated segregation factor, s, obey the Arrhenius relation.
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