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- Friction layer (4)
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TEM-Untersuchungen der Randzonenschädigung von Aluminiumoxidkeramiken nach Schleifbearbeitung
(1996)
Es werden elektronenmikroskopische Untersuchungsergebnisse an Al2O3-Keramiken, die verschiedenen Oberflächenbearbeitungsverfahren unterworfen wurden, vorgestellt.
Die Untersuchungen dienen dem Ziel der Optimierung der Oberflächenbearbeitung von keramischen Werkstoffen, wobei der Einfluß leistungsfähiger Bearbeitungsverfahren auf die Ausbildung möglichst schädigungsarmer Oberflächenschichten, die keinen negativen Einfluß auf Festigkeitskennwerte aufweisen, betrachtet wird.
Die Wirkung verschiedener Schleif- und Polierprozesse auf Oberflächenveränderungen bearbeiteter Werkstücke wird dargestellt. Es wurde sowohl die Mikrostruktur der geschädigten Randzonenschicht als auch die des unbeeinflußten Grundmaterials mit elektronenmikroskopischen Methoden charakterisiert. Die verschiedenen Schädigungsstadien gestatten eine Einschätzung der Stärke des Störungseintrages in das Material durch verschiedene Schleif- und Polierprozesse.
Transmission electron microscopy study of rapid thermally annealed Pd/Ge contacts on IN0.53Ga0.47As
(1996)
X-ray photoelectron spectroscopy (XPS) and cross-sectional transmission electron microscopy (XTEM) were used to study the formation of AlN films by N+2 ion implantation of aluminium at energies of 3 keV and 100 keV. In both cases, a two-stage mechanism was found, comprising first the oriented precipitation of small particles of the hexagonal AlN-phase, followed by growth and coalescence finally forming a continuous AlN-layer while increasing the implantation dose from 1×1017 cm-2 to 2×1017 cm-2. The results of both methods are in excellent agreement and furthermore provide complementary information concerning chemical composition and binding energies as well as microstructural details.
Different wear-resistant coatings produced by physical vapour deposition (PVD) were characterized with the aid of cross-sectional transmission electron microscopy (XTEM). All coating systems were optimized by the producers and exhibited good properties with respect to their special applications. The microstructure, texture and chemical composition of binary and ternary systems produced by the arc process [TiN, CrN, Cr2N (Ti, Cr)N on steel substrates] and magnetron sputtering process [TiN, CrN on steel substrates, (Ti, Al)N on Si-substrate] were investigated. All coatings had a more or less columnar microstructure, which was interrupted by interlayers in some cases. Whereas arc coatings always did show some kind of substrate modification, the latter was not observed after magnetron sputtering. Electron diffraction normally revealed a mono-phase fcc structure, except at sites very near to the interface. Only for the systems CrN and (Ti, Cr)N were different additional phases observed at low nitrogen partial pressures.
The formation of a third body layer on a conventional friction material during braking tests was studied in some detail using TEM, SEM, and X-ray photoelectron spectroscopy (XPS) techniques. Plate shaped micro-contact areas representing a compositional mix of all components of the tribocouple and exhibiting a nanocry stalline microstructure were identified after a run-in period.
The chemical and microstructural changes occurring during braking simulation tests at the surface of a conventional brake pad material were investigated mainly by scanning and transmission electron microscopy and surface analytical techniques. It can be shown that patches of a third body material develop, comprising a compositional mix of all constituents of the pad and iron oxides from the disk. Milled debris particles still have the crystal structure of barite, the major phase of the pad material, but the grain size is reduced drastically to the nanometer scale. The major wear mechanism is delamination of filler particles from the organic binder, supported by local degradation of the phenolic resin during asperity heating. Quartz crystals are preserved thereby adopting the function of primary contact areas.
The surfaces of a brake pad and rotor were investigated after a run-in period during which a stable coefficient of friction had developed. The Focused Ion Beam Technique (FIB) was used to reveal tribologically induced surface films and for cross-sectional preparation of superficial layers. Additional information was obtained by TEM/EDS of thin lamellae prepared with the FIB and by surface analytical methods (GDOS, XPS and RS). Microscopic contact areas of the pad showed bright contrast in Scanning Ion Microscopy (SIM). This was attributed to severe plastic deformation finally leading to a nanocrystalline microstructure. Metallic particles of the pad, the so-called primary contact areas, were mostly covered with a smooth oxide layer of less than 1 µm thickness. Above this layer a thin (100 nm) partly amorphous film was often observed. The film was not only restricted to the metal particles, but also spread over adjacent regions, suggesting that secondary plateaus had formed. Similar layers and films, although with slightly different composition and structure, were also observed at the surface of the rotor.