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Diffusion of C and Mn in steel weldment Fe-0.3C-5Mn/Fe-0.3C-15Mn
Král, Lubomír ; Million, Bořivoj ; Čermák, Jiří
In this paper, the results of measurements of chemical diffusion of Mn and C in weldments of alloys Fe-0,3%C-5%Mn / Fe-0,3%C-15%Mn are reported. Alloys were cast in induction furnace under protective Ar atmosphere. They were hot-forged to rods of diameter 15mm and cut into pieces of 4mm thickness. These cylindrical samples were metalographical polished. Diffusion couples, welded by electrical impulse, were sealed together with Ti-chips, into evacuated silica ampoules. After that, they were annealed at 1100-800 °C for 1.5-96 hours respectively. Measurement of C redistribution was done in a normal direction to welding interface using electron-scanning microscope Philips SEM-505WDS equipped with Microspec WDX-2A. Diffusion coefficients of C and Mn were obtained and the relations between them were found.
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Ab initio study of phase stability in metals
Káňa, Tomáš ; Hüger, E. ; Šob, Mojmír
We employ ab initio calculations to study the behavior of total energy along the transformation paths between the hexagonal close-packed (hcp) structure and face-centered cubic (fcc) structure in Al, Co, Ni, Cu and Pd. We found one peculiar transformation path wit h extremely low energy barrier of only 0.010 eV/atom for Al, 0.020 eV/atom for Pd, 0.030 eV/atom for Cu, 0.033 eV/atom for Ni and 0.050 eV/atom for Co.
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First principles study of polymorfy of Ni and Co thin layers
Zelený, Martin ; Šob, Mojmír
The total energy profiles of trigonal and hexagonal bulk Ni and Co are employed to advance our understanding of epitaxial growth of Ni and Co thin films on various fcc(111) substrates. For nickel films, we predict the fcc stacking in the neighbourhood of the ground state and for the distance of nearest neighbors larger than 5.18 a.u. the film should exhibit hcp layer stacking. Cobalt films behave differently. The hcp phases are energetically more favorable in whole region studied.
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Vzájemná difúze v systému Mg/Mg17Al12
Rothová, Věra ; Čermák, Jiří
Light Mg-based alloys are perspective materials for automotive industry. The presence of the brittle phase Mg17Al12 in the structure of the materials causes, however, certain problems in their production and during the application. It is known that desirable mechanic parameters can be easily achieved by a special annealing which leads to a less-harmful morphology of Mg17Al12 phase. The physical background of the process consists in the diffusion-controlled redistribution of components in the alloy. In the present work, the interdiffusion coefficients were measured in diffusion couples made of Mg and Mg17Al12. The results may contribute to an optimization of production process.
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