TY - JOUR A1 - Österle, Werner A1 - Griepentrog, Michael A1 - Gross, Thomas A1 - Urban, Ingrid T1 - Chemical and microstructural changes induced by friction and wear of brakes N2 - 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. KW - Brake KW - Third body material KW - Friction layer KW - Electron microscopy PY - 2001 U6 - https://doi.org/10.1016/S0043-1648(01)00785-2 SN - 0043-1648 VL - 251 SP - 1469 EP - 1476 PB - Elsevier CY - Amsterdam AN - OPUS4-2371 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Urban, Ingrid T1 - Third body formation on brake pads and rotors N2 - 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. KW - Friction material KW - Friction layer KW - Friction film KW - Third body KW - Brake PY - 2005 U6 - https://doi.org/10.1016/j.triboint.2005.04.021 SN - 0301-679X VL - 39 IS - 5 SP - 401 EP - 408 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-12309 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Urban, Ingrid T1 - Friction layers and friction films on PMC brake pads N2 - A rather new tool, the focused ion beam (FIB) technique, was used to characterise superficial layers at micro-contact areas of a commercial brake pad. The friction material was a polymer matrix composite (PMC) with approximately 50% metal content (semi-metallic) and the counter part was a cast iron rotor. Though the contact areas were not visible as topographic features, they could be identified with the aid of their increased secondary electron emission during FIB-scanning of the surface after tribological activation. Target preparation of micron-sized cross-sections with the FIB enabled the study of superficial layers at predetermined sites at high magnification. Depending on the constituent of the pad, one, two or three layers were identified. The three layer structure comprised: (i) a 100 nm thick friction film containing nanocrystalline metal oxides and an amorphous phase which was enriched with sulphur, (ii) a nanocrystalline friction layer of compacted wear debris accommodating surface roughness and (iii) a severely deformed layer if the supporting constituent was a metal particle. Though the majority of loose wear particles was iron oxide, the friction film which adhered tightly to the pad surface contained a large amount of copper and sulphur, whereas zinc was transferred to the cast iron rotor. KW - Brake KW - Friction film KW - Friction layer KW - Oxidational wear KW - FIB PY - 2004 U6 - https://doi.org/10.1016/j.wear.2003.12.017 SN - 0043-1648 VL - 257 IS - 1-2 SP - 215 EP - 226 PB - Elsevier CY - Amsterdam AN - OPUS4-7645 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -