Papers by Author: Karel Saksl

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Authors: J. Bednarčík, R. Nicula, Karel Saksl, M. Stir, E. Burkel
Abstract: The magnetic, mechanical or chemical properties of nanocrystalline materials strongly differ from the ones of their coarse-grained counterparts. Moreover, significant changes of the phase diagrams were already evidenced for nanostructured alloys. Thermal processing with or without applied pressure controls the microstructure development at the nanometer scale and thus essentially decides upon the final nanomaterial behaviour and properties. A common route for the synthesis of metallic nanomaterials is the devitrification of amorphous precursors obtained via non-equilibrium processing, e.g. by rapid solidification or high-energy ball-milling. Time-resolved in-situ X-ray diffraction experiments may nowadays be performed at high-brilliance synchrotron radiation sources for a variety of temperature-pressure conditions. The temperature-time evolution of the grain-size distribution and microstrain can be monitored in detail at specimen-relevant scales. Together with local information from electron microscopy and chemical analysis, in-situ X-ray experiments offer a complete set of tools for engineering of the microstructure in nanomaterials. The effect of individual processing steps can be distinguished clearly and further tuned. An example is provided, concerning the high-temperature microstructure development in Co-rich soft magnetic nanostructured alloys.
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Authors: Dalibor Vojtěch, Jan Verner, Barbora Bártová, Karel Saksl
Abstract: Rapidly solidified (RS) Al-TM (TM = transition metal) alloys are perspective materials from scientific, as well as technological point of view. Generally, they are produced by the melt atomization or by the melt spinning. Subsequent compaction is commonly performed by the hot extrusion. Since transition metals, such as Cr, Fe, Ni, Zr, Ti, Mn and others, have low diffusion coefficients in solid aluminium (lower by several orders of magnitude than those of common alloying elements like Cu, Si, Mg, Zn etc.) the RS Al-TM alloys are characterized by a high thermal stability. In this paper, several RS Al-TM (TM = Cr, Fe, Ti, Mn, Ni) alloys prepared by the melt spinning and melt atomization are compared to commercially available 2xxx, 6xxx and 7xxx wrought alloys. The main structural features of both RS and wrought alloys are described. The RS alloys are characterized by the presence of micro and nano-scale crystalline and/or quasi-crystalline phases and supersaturated solid solutions. The elevated-temperature behaviour is compared for both groups of materials. The thermal stability of the investigated materials is determined by room temperature hardness measurements after various annealing regimes and a high thermal stability of the RS alloys is demonstrated. The microstructural changes and phase transformations occurring in the investigated materials upon heating are described. In the Al-TM alloys, very slow decomposition of the supersaturated solid solutions, precipitation and decomposition of the metastable quasi-crystalline phases occur.
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