|
|
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.
|
|
| |
|
|
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.
|
|
| |
|
|
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.
|
|
| |
|
| |
|
|
Preparation and properties of nanocomposites based on Zr-Fe
Roupcová, Pavla ; Schneeweiss, Oldřich ; Bezdička, Petr
The spark erosion of the pure Zr and Fe electrodes in hydrogen yielded nanocrystalline powder consisting of the mixture of Zr-rich (Zr3FeH7, ZrO2, and Zr(Fe)) and Fe-rich phases with the mean chemical composition Zr-3.2wt.%Fe. Heat treatment in hydrogen atmosphere at 973K induced phase decomposition and transitions with the final composition of bcc Fe, Zr3Fe, ZrH2 and dominating ZrO2 phases. The result indicates that formation of Fe-rich phase (bcc Fe) embedded in ZrO2 could be possible using an appropriate heat treatment of the as-prepared powder.
|
guest ::
