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- 2015 (6) (entfernen)
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- Tribofilm (3)
- (Mn,Ga) As crystallites (1)
- Ball milling (1)
- Bärninghausen symmetry trees (1)
- Cross-sectional TEM (1)
- Focused ion beam (1)
- Gallium implantation (1)
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Eingeladener Vortrag
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The composition and nanostructure of a beneficial tribofilm formed during sliding of a hybrid nanocomposite against steel were characterized comprehensively. A similar nanostructure was produced by high energy ball milling of the three identified tribofilm constituents: silica, hematite and graphite. By supplying powders to a pin-on-disc test it has been shown that neither silica, nor hematite, nor a mixture of both provide the low coefficient of friction (COF) observed for the hybrid composite. Only if graphite was blended with the oxides, the low COF was obtained. Thus, a film of finely dispersed stable inorganic wear products containing 15 vol% graphite provides low friction and wear in the considered case.
The objective of the present work was to study the impact of Focused Ion Beam (FIB) machining parameters on the thickness of the damaged layer within a thin film PZT. Therefore, different Ga+- ion doses and ion energies were applied to a standard PZT film (80/20 lead zirconium titanate) under two beam incidence angles (90° and 1°). The thicknesses of the corresponding Ga+-implanted layers were then determined by cross-sectional TEM in combination with energy dispersive spectroscopic (EDS) line-scans and correlated with polarisation hysteresis loops. The results show a decrease of Ga+-implanted layer thickness with decreasing inclination angle, whereas ion energy and ion dose could be correlated with gallium concentration in the implanted layers.. Under the most unfavorable conditions the depth of the affected zone was 26 nm, it was only 2 nm for the most favorable conditions.
We applied a combination of Raman spectroscopy (RS) and cross-sectional transmission electron microscopy (X-TEM) to identify silicone oil residues and tribofilms at steel disc surfaces after tribological testing. Neither chemical cleaning nor mechanical removal of a 50 µm thick surface layer produced a surface without any silicone residue. Nevertheless, long-term tribological properties are not affected due to silicone degradation which has been proved by Raman spectroscopy. Excellent anti-wear and anti-friction properties of a nanocomposite at severe stressing conditions correlated with the formation of a silica-based tribofilm containing amorphous and graphite-like carbon nanoparticles. Since reliable carbon quantification by analytical TEM is difficult, RS is a useful complementary method for carbon identification at wear scars.
Metal organic vapor phase epitaxy (MOVPE) of Mn-rich (Mn,Ga)As on (001) oriented GaAs wafers resulted in atomically ordered (Mn,Ga)As crystallites of two morphological kinds, partially embedded on the wafer surface and fully embedded within the single crystalline matrix. While the former were apparently free of defects (other than unavoidable point defects), the latter contained two domains separated by a grain boundary. Since atomic ordering can be modeled by space group symmetry descent considerations (Bärnighausen trees) that start with the space group of the known crystallographic phases of random (Mn,Ga)As alloys with specified chemical compositions, reasonable structure hypotheses have been derived for two atomically ordered Mn0.75Ga0.25As phases that we call the trigonal α' and the monoclinic β' phases. The implications of these structure hypotheses are in agreement with the results of a range of scanning transmission electron microscopy (STEM) and parallel illumination electron diffraction (ED) studies that include quantitative energy dispersive X-ray spectroscopy, X-ray spectroscopic imaging, as well nanobeam diffraction and high angle precession ED. The coexistence of two domains within the fully embedded crystallites is predicted by the corresponding Bärnighausen tree and observed experimentally for the fully embedded crystallites.
Formation and function mechanisms of nanostructured tribofilms of epoxy-based hybrid nanocomposites
(2015)
The nanostructures and properties of the tribofilms of epoxy (EP) composites filled with short carbon fibers (SCF) and different volume fractions of monodisperse silica nanoparticles were investigated. When the conventional composite filled only with SCF was considered under a high pv condition, an iron oxide layer is formed on the steel counterface. The addition of even only 0.05 vol% nano-silica leads to a significant change of the tribofilm's structure and the tribological behavior of the composite. With increasing silica content, the oxidation layer on the steel surface is gradually replaced by a silica-based tribofilm. A close relationship between the tribofilms structure and the tribological behavior of the composites was identified. Mixing, possible reactions and tribo-sintering of silica nanoparticles with other wear products are deemed to be main mechanisms inducing the formation and the lubricity of the silica-based tribofilm.