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Počítačová implementace mikro MKP
Blaheta, Radim ; Krečmer, Karel
This paper concerns a special application of the finite element method (FEM), which is modelling of microstructure of materials. This “micro” application of FEM brings some specific features, which can be exploited in the numerical realization and computer implementation of the method. These features are briefly discussed in this paper and will be further developed in a future work.
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Improvement of mechanical properties of the sintered ceramics by plasma remelting
Ctibor, Pavel
Ways how to improve mechanical properties on a surface of bulk ceramics are drawn. In the experiments the author reach surface treatment by plasma torch producing thermal plasma and usually utilized for plasma spraying. Commercial bulk ceramic materials produced via sintering or casting were tested. The materials were members of ternary systems magnesia - alumina - silica and zirconia - alumina - silica. Before and after thermal treatment the microstructure was studied and the microhardness was measured on materialographically polished cross sections using Vickers indentation (HV) in surfacial layers and also deep inside the bulk body. Slurry abrasion resistance (SAR) was determined according ASTM G 75 standard. Various degree of improvement of HV and SAR was detected on treated samples. The microstructural character of completely remolten surfacial layer, partly influenced intermediate layers and original bulk body is discusses in connection with evaluated mechanical tests.
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Redistribuce napětí a její vliv na precipitaci v mikrostruktuře
Holec, David ; Dlouhý, Antonín
The present study considers two mechanisms that can contribute to the local redistribution of stresses in the microstructure of engineering alloys. The first model takes into account the anisotropy of thermal expansion coefficients and predicts a stress state generated close to a boundary between two differently oriented grains after a temperature change. The second model addresses a stress distribution in a polycrystalline aggregate characterized by anisotropic elastic constants and subjected to the isothermal aging under the assistance of external stress. The influence of local stress states on the selective precipitation of the Ni4Ti3 crystallographic variants in the microstructure of the NiTi shape memory alloy is demonstrated.
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Study of quarternary Ni-base alloys
Picha, R. ; Buršík, Jiří ; Brož, P.
Phase structure of Ni-Al-Cr-Ti and Ni-Al-Cr-Ta alloys was studied at 1000 and 1100C by means of analytical electron microscopy.The coexistence of phases, their compositions and phase ratios in studied alloys showed good agreement with calculations.
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Metallography of gamma TiAl intermetallic casts
Dlouhý, Antonín ; Válek, Robert ; Svoboda, Milan ; Zemčík, L.
A quantitative metallographic study was performed which focussed on the cast versions of advanced intermetallic alloys based on gamma TiAl phase. Specimens cut out of cast rods and turbine blades exhibited two pronounced microstructural characteristics: (i) a preferential orientation of lamellae in columnar grains below the cast surface and (ii) increasing fraction of equiaxed grains towards the central part of the casts. The relation between the particular microstrucrure and creep strength has been documented.
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Quasicrystals in 11Cr-3W-3Co Steel
Výrostková, A. ; Svoboda, Milan ; Ševc, P. ; Janovec, J. ; Grabke, H. J.
The microstructural and phase analysis after relaxation strength tests performed at 480, 540 and 570 °C of 10Cr3WVNbB steel TAF 650 and after long term ageing at 480 and 600 °C of 10Cr1Mo1WVNbN steel were carried out. Laves phase in TAF 650 can be denoted as Fe2W type and in the 10Cr1Mo1WVNbN steel as Fe2Mo type Quasicrystalline phase of the same chemical composition as Laves phase was found in TAF 650 steel in all states examined.
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