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National Repository of Grey Literature 2 records found  Search took 0.01 seconds. 
METALLURGY AND PROPERTIES OF ADVANCED NiAl-Mo EUTECTICS
 Barták, Tomáš ; Kuchařová, Květa ; Záležák, Tomáš ; Dlouhý, Antonín
A NiAl-Mo eutectic alloy was melt from 99,99% purity components and cast by the drop casting technique. The drop-cast ternary alloy (nominal composition of Ni-45Al-9Mo at. %), was re-melted and directionally solidified using a high temperature optical floating zone furnace. A resulting in-situ composite consists of Ni-45,2Al matrix and Mo-10Al-4Ni fibers, all in at. %. The volume fraction of 14% Mo-fibers stems from the eutectic composition. Spacing and a diameter of Mo-fibers can be controlled within certain limits using different growth rates of the crystals. Microstructural parameters of the as-cast crystals were assessed by light microscopy, scanning and transmission electron microscopy. Backscatter diffraction shows that the NiAl-matrix and the Mo-fibers are both < 001 >-oriented with respect to the axis of the cylindrical rods. Preliminary creep experiments confirmed an immense improvement of high temperature strength due to the fine distribution of Mo-fibres. The amount of strengthening in terms of minimum creep rate can be as high as 7 orders of magnitude. Post-mortem transmission electron microscopy experiments provided evidence that creep in the temperature range of 800-900 degrees C results in an extensive formation of subgrain boundaries. The strengthening effect is very likely associated with the reactions between subgrain boundaries and fine Mo-fibres.
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Tungsten cermets with zirconium and hafnium carbides
 Brožek, Vlastimil ; Ctibor, Pavel ; Matušek, M. ; Sedláček, J.
Cermets with tungsten matrix and functional components of ZrC and HfC with absolutely highest meeting points are materials with good properties at high temperature exposure. Tungsten based cermets with 10, 20 and 30 % of the functional component were prepared by two different procedures and their properties were compared. The first series of the samples was manufactured by powder metallurgy. A homogenized and preformed mixture of powders was sintered at 2000°C and pressure 6 GPa by hot-pressing technique in the apparatus of BELT-type. The second series was prepared by plasma spraying with water-stabilized plasma WSP® by two different procedures. In the first case the powders of W and ZrC (or W and HfC) were injected into the plasma jet by two separate feeders. The feeding distance 25 to 75 mm was affected by different kinetic parameters, different size distribution and density. The second case represents deposition of pre-spheroidized powder mixtures prepared by spray drying
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