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Atomistické simulace uspořádávání v niklových slitinách pod vlivem mechanického napětí
Buršík, Jiří
Systems containing up to six alloing elements typical of advanced Ni-based superalloys were modelled.their ordering was simulated at atomic level using a Monte Carlo approach with púeriodic boundary conditions and Kawasaki dynamics.molecular dynamics routines were embedded into standard kinetic Ising model to account for relaxing of local atomic positions.Straining computer experiments show that elastic parameters and bulk modulus undergo comparatively large changes at the beginning of ordering process.
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Ab initio studie Lavesových fází v systémech Fe-Cr, Fe-Mo a Fe-Ta
Houserová, Jana ; Šob, Mojmír
Binary systems Fe-Cr, Fe-Mo and Fe-Ta can be found in many kinds of steels where the Laves-phase can be considered as a potential candidate for strengthening provided size and distribution of the particles are within certain limits. We performed electronic structure calculations to study the thermodynamic and structural properties of the C14 Laves phase with various compositions. In the frame of the thermodynamic study, we have evaluated the total energies of formation of Laves phase structure with different occupations of sublattices (Fe2Fe, Fe2X, X2Fe, X2X, where X stands for Cr, Mo and Ta) with respect to the Standard Element Reference (SER) states. These energies of formation are of great importance for prediction of stability of studied configurations.
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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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Diffusion of C and Mn in steel weldment Fe-0,3C/Fe-0,3C-15Mn
Král, L. ; Million, Bořivoj ; Čermák, Jiří
In the present paper, the results of measurements of C and Mn diffusion in steel weldments of ternary alloys Fe-0.3C/Fe-0.3C-15Mn are reported. Alloys were cast in induction furnace under protective Ar atmosphere. Ingots were hot-forged to rods of the diameter 15mm and homogenized. After annealing they were machined on diameter 12mm and cut into pieces of 4mm thickness. These cylindrical samples were ground and welded by electrical impulse. Diffusion couples were sealed into evacuated silica ampoules together with Ti-chips. They were annealed at 500-1100 °C for 1.5-96 hours. Measurement of carbon and manganese redistribution was done by means line segment microanalysis in normal direction to welded interface using electron scanning microscope Philips SEM-505WDS equiped with Microspec WDX-2A. Diffusion coefficients of C and Mn were obtained and the relations between them were found.
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