National Repository of Grey Literature 30 records found  beginprevious18 - 27next  jump to record: Search took 0.00 seconds. 
THE EFFECT OF MO AND/OR C ADDITION ON MICROSTRUCTURE AND PROPERTIES OF TIAL ALLOYS
Chlupová, Alice ; Kruml, Tomáš ; Roupcová, Pavla ; Heczko, Milan ; Obrtlík, Karel ; Beran, Přemysl
Cast TiAl alloys with high Nb content are subject of extensive research with the aim to develop material with low density, good corrosion resistance and high strength at elevated temperatures. Disadvantage of their broad applications is restricted workability, machinability and low fracture toughness especially at room temperature. Improvement of properties of TiAl based materials can be achieved by tailoring the microstructure by modification of chemical composition. For this purpose 5 types of TiAl alloys with 7 % of Nb were prepared having variable content of Mo and/or C. Addition of Mo and/or C resulted in three types of microstructure and different phase composition. All modified alloys contain colonies consisting of thin lamellae of a and g phases sometimes complemented by g and/or b phase at the grain boundaries. Variable microstructure and phase composition resulted in differences in mechanical behaviour. The most promising tensile properties at both room and elevated temperature were observed for alloy doped with 2 % of Mo having the mixed microstructure containing b phase and for alloy doped with 0.5 % of C with nearly lamellar microstructure without b phase. 2Mo alloy exhibited reasonably good ductility while 0.5C alloy reached the highest tensile strength. Also low cycle fatigue behaviour of these two materials was the best of all five materials under investigation. Fatigue deformation characteristics were better in the case of 2Mo alloy while 0.5C alloy exhibited higher cyclic stresses. Fracture mechanisms were determined using fractographic analysis. The major fracture mode of all alloys was trans-lamellar.
Analysis of nanoparticles released from the car brakes
Švábenská, Eva ; Roupcová, Pavla ; Schneeweiss, Oldřich
Our research is focused on the phase, structure and chemical analysis of the powder particles released by braking of cars from their brake components – discs and pads. The basic information on structure and phase composition was obtained by X-Ray Powder Diffraction, Mössbauer Spectroscopy and scanning electron microscopy with EDX. The results of the particle analysis are compared with materials used for manufacturing brake components and with the powder prepared by ball milling of the mixture of the pad composite and disk steel. Most of recognized nanoparticles are based on carbon, silica/silicates and iron oxides. Their effects on street environment are mentioned.
Analysis of the surface layer of the brake disk
Švábenská, Eva ; Roupcová, Pavla ; Podstranská, Ivana ; Petr, M. ; Filip, J. ; Schneeweiss, Oldřich
Our research is focused on the changes in thin surface layer of the brake disk due to the impact of severe plastic deformation and heating by friction process. The aim of this study is to compare structure, chemical and phase compositions of the surface layer in depth up to several hundreds of nanometers in the no affected central part of brake disk and the part which was in contact with brake pads by braking. The basic information on structure and phase composition was obtained by optical and scanning electron microscopy, X-Ray Powder Diffraction and Mössbauer Spectroscopy. The thin surface layer was studied using Conversion Electron Mössbauer Spectroscopy and X-ray Photoelectron Spectroscopy. We explain the observed changes with the knowledge on effects of plastic deformation and/or diffusion of alloying elements in the material of the brake disk.
PREPARATION OF FE-TI COMPOSITES BY BALL MILLING
Roupcová, Pavla ; Schneeweiss, Oldřich
The similar Ti-Fe powders were prepered from pure precursors as well as from splinters. The difference of structural and phase composition was determined by XRD and Mössbauer spectroscopy.
Příprava Fe-Ti kompozitů mletím v kulovém mlýnku
Roupcová, Pavla ; Schneeweiss, Oldřich
The materials were prepared by mechanical alloying in the ball mill. The first type of sample consists of pure commercial precursors (TiH2 and ferrihydride). The slightly changes of phase composition of the powder were under the detection limit of X-ray powder diffraction. The MS determined the changes from the first step of milling. The second type of sample was prepared from turnings. The reduction of the splinters volume and the mechanical alloying was running simultaneously. The huge crystalline size differences decreased the credibility of computation of phase composition by XRD. MS was able determined phase composition more exactly and in additional to differentiate crystalline and amorphous FeTi phase.
Changes of Phase Composition of NaAlH4 Based Complex Hydrides
Roupcová, Pavla ; Schneeweiss, Oldřich
The Mössbauer study is target to valence of Fe-doped phase and its changes during preparation by mixing with NaAlH4 and charging and discharging cycles. The 2 mol % FeCl2·4H2O powder was contained in the asmixing material. The dry milled sample did not transformed during the milling in the protective atmosphere. The significant change was approved in the firstly hydrogenation step only. The analysis shows FeClO which released the most significant component in the dehydrogenation and hydrogenation steps. The amount of FeClO was decreased with the all following step of hydrogenation and dehydrogenation. The fine paramagnetic particles of iron oxides were detected and their amount increased influenced of gas impurities. The longer period of heat treatment shows the agglomeration of iron oxides and their magnetic effect.
Microstructure, tensile properties and fatigue behaviour of bulk nanoquasicrystalline Al alloy Al93Fe3Cr2Ti2
Chlupová, Alice ; Chlup, Zdeněk ; Kruml, Tomáš ; Kuběna, Ivo ; Roupcová, Pavla
The characterization of mechanical properties (i.e. stress-strain characteristics measured in tensile and fatigue tests) together with description of the microstructure of bulk nanocrystalline Al alloy is reported. Aluminium based material used in this work was prepared by hot extrusion of gas atomised powder of chemical composition Al93Fe3Cr2Ti2 which contains nanosized quasicrystalline phase. Changes in fracture mechanisms both at fatigue testing performed at room temperature and at tensile tests performed at different test temperatures were investigated. The quality of powder compaction after extrusion was proved as sufficient. Strong texture in longitudinal direction resulting from production route was detected. Presence of icosahedral phase in material was confirmed by TEM and XRD techniques. Fractographical analysis of fracture surface was performed and results were used for description of fracture mechanisms.
Properties of nanocrystalline powder based on Fe-Zr
Roupcová, Pavla ; Schneeweiss, Oldřich
The phase composition of nanocrystalline Zr–Fe powder prepared by spark synthesis was investigated by means of Mossbauer spectroscopy, X-ray diffraction and magnetic measurements. The ability of hydrogen absorption is decreasing with the annealing steps and is connected with the increase in Fe2Zr phase content.
Vlastnosti nanokrysltalického Zr-Fe-H
Roupcová, Pavla ; Schneeweiss, Oldřich
In this paper, we describe some results obtained by synthesis of Fe-Zr alloys and the study of the phase transformations in these materials induced by hydrogen. Mossbauer spectroscopy was used as the most sensitive method for determination of Fe-Zr based phases in a nanocrystalline form.
Nanočástice Fe a Fe3O4 v matrici ZrO2
Roupcová, Pavla ; Schneeweiss, Oldřich
Changes in the phase composition and the mean particles size of nanocrystalline Zr-Fe powdered prepared by mixing of pure ZrO2 and iron oxides were investigated in dependence of the heat treatment in vacuum and hydrogen atmosphere.

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