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 - Kloß, Heinz A1 - Urban, Ingrid A1 - Dmitriev, A.I. T1 - Towards a better understanding of brake friction materials N2 - This work focuses on surface changes induced by repeated brake applications and tries to provide explanations, how such material modifications might affect friction and wear properties of automotive disc brakes. Surface films were investigated locally by transmission electron microscopy (TEM) after having prepared thin cross-sections with a focused ion beam instrument (FIB). Since the observed friction layers revealed a nanocrystalline structure, modelling with the method of movable cellular automata (MCA) was performed by assuming an array of linked nanometer-sized particles. In spite of complicated material combinations at the pad surface, two very characteristic features were always observed at both the pad and disc surface, namely a steel constituent—either ferritic (pad) or pearlitic (disc), partly covered with patches of nanocrystalline iron oxide, on a zone of severe plastic deformation with fragmented grain structure. When using an automata size of 10 nm, reasonable values for the mean coefficient of friction (COF) were obtained, namely 0.35 and 0.85 for oxide-on-oxide and metal-on-metal contacts, respectively. Immediately after brake application mass-mixing and bond-breaking was observed within a narrow zone at both surfaces. KW - Brake pad KW - Brake disc KW - Composite material KW - Friction layer KW - Third body KW - MCA-modelling PY - 2007 U6 - https://doi.org/10.1016/j.wear.2006.12.020 SN - 0043-1648 VL - 263 IS - 7-12 SP - 1189 EP - 1201 PB - Elsevier CY - Amsterdam AN - OPUS4-15735 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -