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New types of lead-free solders and their properties
Drápala, J. ; Petlák, D. ; Malcharcziková, J. ; Vodárek, V. ; Konečná, K. ; Smetana, B. ; Zlá, S. ; Kostiuková, G. ; Seidlerová, J. ; Lasek, S. ; Madaj, M. ; Kroupa, Aleš ; Urbánek, J. ; Dušek, K. ; Sedláček, J. ; Sidorov, V.E.
Ternary and binary alloys with different ratios of Ag, Al, Bi, Cu, In, Mg, Sb, Sn and Zn were prepared experimentally. The following characteristics were studied: temperatures and enthalpies of phase transformations (DTA, TG, DSC), macro-and micro-structural analysis, micro-hardness, chemical analysis, X-ray and density measurements and electrical resistivity of selected solders, test of wettability with or without use of fluxes, measurement of corrosion properties.
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Effect of plasma sprayed AlSi coating on low cycle fatigue properties of cast superalloy Inconel 738LC
Obrtlík, Karel ; Pospíšilová, S. ; Juliš, M. ; Čelko, L. ; Podrábský, T.
Air plasma spraying was applied to obtain AlSi protective surface coating on cylindrical specimens of cast polycrystalline superalloy Inconel 738LC. Chemical composition of the surface treated layer was studied and the hardness depth profile was measured. Surface treated and untreated specimens were cyclically strained under total strain control at 800 °C in air. Cyclic stress-strain response and fatigue life of both materials were obtained. The coating results in a slight decrease of cyclic stress-strain curve. A detrimental effect of the surface treatment on derived Wöhler curve is documented while Manson-Coffin curves of both materials are almost identical. Specimen section observations and fracture surface examinations help to discuss fatigue behaviour of both materials.
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Microstructure Stability and Creep Behaviour of Alloys Processed by ECAP
Dvořák, Jiří ; Král, Petr ; Svoboda, Milan ; Kvapilová, Marie ; Sklenička, Václav
Coarse-grained binary Cu and Al alloys were processed by equal-channel angular pressing (ECAP) in order to evaluate the effect of severe plastic deformation on the thermal stability of resulting ultrafine-grained microstructure after ECAP followed by creep loading of the pressed alloys. ECAP was conducted at room temperature with a die that had an internal angle of 90° between the two parts of the channel. The subsequent extrusion passes were performed by route Bc. Microstructure of samples up to 12 ECAP passes was characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM) equipped with the electron backscatter diffraction (EBSD) unit. Constant load creep tests in tension were performed at 0.3 - 0.5 Tm and at different applied stresses. It was found that the creep behaviour is influenced by high-angle grain boundaries created by ECAP and creep fracture occurred along the shear bands which are situated near shear plane of the last ECAP pass.
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Influence of Microstructure Instability on Creep Behaviour of UFG Pure Materials
Král, Petr ; Dvořák, Jiří ; Svoboda, Milan ; Kvapilová, Marie ; Sklenička, Václav
Experiments were conducted to determine an effect of creep temperature on creep behaviour of pure Cu. The ECAP pressing was performed at room temperature by route Bc. Constant load creep tests in tension were conducted at 373-573 K under different stresses. The values of the stress exponent n of the minimum creep rate for ultrafine-grained (UFG) and coarse-grained material were determined. Microstructure of samples was characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM) equipped with the electron backscatter unit (EBSD). The microstructure analyses showed that microstructure of pure Cu processed by 8 ECAP passes and subsequent creep exposure contained large fraction of boundaries with coincidence sites lattice (CSL). The results showed that creep in UFG materials is influenced by additional creep mechanisms up to 0.5 Tm when the UFG microstructure in more or less stable.
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Measurement of Carbon Diffusion Coeficient - Calibration of Sputter Depth
Král, Lubomír ; Čermák, Jiří
Depth profiling mode of MiniSIMS device was applied to diffusion measurement. Calibration of crater depth was done using shearing interference microscope Zeiss Epival Interphako (ZEI) and confocal mikroskope Olympus LEXT OLS3100 with atomic force microscopy (AFM) modul. The ZEI uses one of the classical interferometric measuring methods. Generally this method leads to results with considerable experimental error. AFM is a very high-resolution type of scanning probe microscopy, with typical resolution of the order of fractions of nanometers, which is more than 1000 times better than the optical diffraction limit. However, the results taken by ZEI were in agreement with much more precise results of surface profiling achieved by AFM. It was found, at given experimental conditions (Fe-rich matrix, Ga + primary ions, 5 kV/3nA, DWT=1), that the sputter rate is some 0.3 nm per a single sputter scan of the crater area (50x50 µm). This depth calibration with SIMS technique can be applied to the study of carbon diffusion in BCC iron as an example. Special technique was developed, which avoids radio-tracer measurements with C-14. Obtained results are lower than the extrapolated values, which may be due to limited solubility of carbon in iron.
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Hydrogen Storage Capacity of Mg/Mg2Ni Eutectic Doped with Elements from Groups XIII and XIV
Čermák, Jiří ; Král, Lubomír
In the present paper, the chemical composition of Mg-8.5 at.% Ni-2.7at.%X alloys (X – elements of the 13th and 14th groups) as prospective hydrogen storage was investigated. Experimental alloys were studied in three states: (i) after stabilization anneal, (ii) after stabilization anneal and hydrogen charging, and (iii) after stabilization anneal, hydrogen charging and hydrogen desorption. It was ascertained that a ratio of concentration of X in two principal phases – Mg2NiH4(-X) and MgH2(-X) – was a decreasing function of the ionization potential of X. The stronger the preference of X for Mg2NiH4-X phase, the higher the hydrogen storage capacity of Mg-Ni-X alloy was. For X = In, the hydrogen storage capacity was slightly higher than the capacity of an un-alloyed binary eutectic Mg-Ni alloy.
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Improvement of Hydrogen Desorption Characteristics of Eutectic Mg/Mg2NiH4 and Mg2NiH4 by In addition
Čermák, Jiří ; Král, Lubomír
Mg-xNi alloys are known as perspective hydrogen storage materials [1,2]. Hydrogen storage capacity and hydrogen desorption rate of binary alloys Mg-Ni are, however, still unsatisfactory and therefore, improvements are sought, e.g., by introduction of a proper catalyst [3]. As candidate elements, transition metals [4] are often used that attract bonding valence electrons and, hence, destabilize the hydrides. However, also elements with weaker bond to H than that of Mg, or even non-hydride forming elements show a beneficial effect upon the hydrogen desorption rate [5,6]. The present investigation continues our previous work [7,8]. Here we investigate the resistance of eutectic Mg/Mg2Ni against the poisoning by residual air and possible ways how to improve the hydrogen desorption kinetics of Mg2NiH4 by doping. As dopants, elements of the 13th and the 14th group were tested that do not form stable hydrides.
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Microstructure Characterization and Faigue Behavior of Beta Phase Containing Gama-TiAl Alloy
Petrenec, Martin ; Beran, Přemysl ; Šmíd, Miroslav ; Chlupová, Alice ; Kuběnová, Monika
The microstructure and fatigue properties of Ti–44Al–7.8Nb – 0.2Ni (at.%) alloy after graded cooling heat treatment were investigated. Different techniques as SEM, TEM and FIB were used for characterization of microstructure. Quantification of phase volume fraction was measured by neutron diffraction method. After graded cooling heat treatment the structure consists of fully lamellar uniform grains which contain lamellar phases /2 and cubic phases (ordered B2 and disordered phases) at grain boundary and interlamellar spaces. The foils for TEM were prepared using FIB technique and observed in TEM in order to identify B2 phase by selected electron diffraction. Low cycle fatigue behaviour at 750 °C shows stable fatigue crack propagation due the presence of plastic beta and B2 phases.
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