TY - JOUR A1 - Österle, Werner A1 - Urban, Ingrid A1 - Severin, D. A1 - Trepte, S. T1 - Correlations between surface modification and tribological performance of brake pads JF - Surface engineering N2 - 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. PY - 2001 DO - https://doi.org/10.1179/026708401101517700 SN - 0267-0844 SN - 1743-2944 VL - 17 IS - 2 SP - 123 EP - 125 PB - Institute of Metals CY - London AN - OPUS4-2367 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 JF - Tribology International 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 DO - 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 JF - Wear 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 DO - 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 - TY - JOUR A1 - Österle, Werner A1 - Rooch, Heidemarie A1 - Pyzalla, A. A1 - Wang, L. T1 - Investigation of white etching layers on rails by optical microscopy, electron microscopy, X-ray and synchrotron X-ray diffraction JF - Materials science and engineering A N2 - Patches of white etching layers on rail surfaces were investigated using sophisticated techniques like cross-sectional transmission electron microscopy (XTEM) and synchroton X-ray diffraction. Optical microscopy failed to resolve the microstructure, but in the TEM submicron grains with high dislocation densities and occasional twins, which are characteristic features of high carbon martensite, were observed. The martensitic structure was confirmed by evaluation of synchroton X-ray diffraction line profiles. The latter technique also allowed to determine dislocation densities of the order of 1012 cm-2 and residual compressive stresses of about 200 MPa. KW - Cross-sectional transmission electron microscopy KW - White etching layers KW - X-ray diffraction PY - 2001 DO - https://doi.org/10.1016/S0921-5093(00)01842-6 SN - 0921-5093 SN - 1873-4936 VL - 303 SP - 150 EP - 157 PB - Elsevier CY - Amsterdam AN - OPUS4-2370 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Ressel, P. T1 - XTEM investigation of Ge/Pd shallow contact to p-IN0.53Ga0.47As JF - Materials science & engineering B N2 - Cross-sectional transmission electron microscopy, in combination with energy dispersive X-ray spectroscopy and focused beam microdiffraction, was applied to study the solid-state reactions taking place during contact formation of the system Ge(115 nm)/Pd(50 nm)—In0.53Ga0.47As. In order to get information about the sequence of the different processes, rapid thermal, annealing experiments in the range 225–400 °C were performed. The following features were observed: at 225 °C Pd reacted with the substrate forming the quaternary phase PdxIn0.53Ga0.47As (x ˜ 4), and with the Ge-layer forming mainly PdGe and Pd2Ge. Between PdxIn0.53Ga0.47As and In0.53Ga0.47As, a 5 nm thick amorphous Pd-In-Ga-As layer remained, indicating that the first reaction step was solid-state amorphization. After annealing at 350 °C, PdxIn0.53Ga0.47As disappeared and regrowth of In0.53Ga0.47As occured. Finally, at 400 °C, residual Ge from the amorphous top layer diffused to the interface and grew epitaxially on the regrown In0.53Ga0.47As, thus separating the III–V compound semiconductor from the Pd-Ge reaction products. The interface remained flat, while only about 10 nm of the active In0.53Ga0.47As layer had been modified during the annealing processes. PY - 1996 DO - https://doi.org/10.1016/0921-5107(96)01580-2 SN - 0921-5107 SN - 1873-4944 VL - 40 IS - 1 SP - 42 EP - 49 PB - Elsevier CY - Amsterdam AN - OPUS4-2513 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Prietzel, Claudia A1 - Kloß, Heinz A1 - Dmitriev, Andrey T1 - On the role of copper in brake friction materials JF - Tribology International N2 - Copper is a major ingredient in friction materials used for automotive braking. The purpose of this study was to find out how copper contributes to good brake performance properties in addition to providing good thermal conductivity. Microstructural investigations of copper chips at the surfaces of brake pads revealed a zone of severe plastic deformation which provides high hardness, but there is also evidence of recrystallized copper nano-particles which are incorporated into friction layers as soft ingredient once detached from the pad surface. Thus copper seems to play a dual role, firstly as reinforcing element of the brake pad providing primary contact sites, and secondly as solid lubricant by contributing to the formation of a layer of granular material providing velocity accommodation between the rotating disc and fixed pad. Confirmation for this hypothesis was obtained by modelling contact sites on the nanometre scale with the method of movable cellular automata. Results show both, the similarity of steel fibres and copper macro-particles in respect to providing primary contact sites, as well as similar sliding behaviours of friction layers containing either copper or graphite as soft inclusions. Furthermore, it is shown that not only material properties, but also the concentration of solid lubricant particles in the friction layers, determine conditions for friction force stabilization and smooth sliding behaviour. KW - Friction material KW - Friction layer KW - Copper macro-particle KW - Copper nano-particle PY - 2010 DO - https://doi.org/10.1016/j.triboint.2010.08.005 SN - 0301-679X VL - 43 IS - 12 SP - 2317 EP - 2326 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-22342 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Prietzel, Claudia A1 - Dmitriev, Andrey T1 - Investigation of surface film nanostructure and assessment of its impact on friction force stabilization during automotive braking JF - International journal of materials research N2 - The unique nanostructure formed during severe as well as moderate braking on the surface of brake discs was investigated by conventional and analytical Transmission Electron Microscopy. In both cases nanocrystalline magnetite mixed with carbon nanoinclusions and minor amounts of other pad constituents were identified. On the basis of these observations the friction performance of a single micro-contact was simulated with the method of Movable Cellular Automata. Inspite of a simplified nanostructure which was examined in two dimensions only, the calculated mean coefficient of friction fitted well to the value usually demanded for automotive braking. Furthermore, the model predicts that oxide films without soft nanoinclusions are not capable of providing smooth velocity accommodation at the pad–disc interface and thus lead to unstable friction behaviour. KW - Friction KW - Third body film KW - Nanostructure KW - MCA-model KW - EFTEM PY - 2010 SN - 1862-5282 VL - 101 IS - 5 SP - 669 EP - 675 PB - Carl Hanser CY - München AN - OPUS4-22343 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Orts Gil, Guillermo A1 - Gross, Thomas A1 - Deutsch, Cornelius A1 - Hinrichs, R. A1 - Vasconcellos, M.A.Z. A1 - Zoz, H. A1 - Yigit, D. A1 - Sun, X. T1 - Impact of high energy ball milling on the nanostructure of magnetite-graphite and magnetite-graphite-molybdenum disulphide blends JF - Materials characterization N2 - Different, partly complementary and partly redundant characterization methods were applied to study the transition of magnetite, graphite and MoS2 powders to mechanically alloyed nanostructures. The applied methods were: Transmission electron microscopy (TEM), Mössbauer spectroscopy (MS), Raman spectroscopy (RS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The main objective was to prepare a model material providing the essential features of a typical tribofilm forming during automotive braking, and to assess the impact of different constituents on sliding behaviour and friction level. Irrespective of the initial grain size, the raw materials were transferred to a nanocrystalline structure and mixed on a nanoscopic scale during high energy ball milling. Whereas magnetite remained almost unchanged, graphite and molybdenum disulphide were transformed to a nanocrystalline and highly disordered structure. The observed increase of the coefficient of friction was attributed to a loss of lubricity of the latter ingredient due to this transformation and subsequent oxidation. KW - Ball milling KW - Mössbauer spectroscopy KW - Raman spectroscopy KW - Transmission electron microscopy KW - X-ray diffraction KW - X-ray photoelectron spectroscopy PY - 2013 DO - https://doi.org/10.1016/j.matchar.2013.09.007 SN - 1044-5803 SN - 1873-4189 VL - 86 SP - 28 EP - 38 PB - Elsevier Inc. CY - New York, NY AN - OPUS4-29697 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Nebauer, E. A1 - Hilsenbeck, J. A1 - Würfl, J. A1 - Klein, A. T1 - XTEM and TFXRD investigations of ohmic Ti/Al/Ti/Au/WSiN contacts on AlGaN/GaN HFET layer systems JF - Semiconductor science and technology N2 - The microstructural features of the high-temperature-stable ohmic contact system Ti/Al/Ti/Au/WSiN on AlGaN/GaN were investigated using analytical transmission electron microscopy and thin film x-ray diffraction. For two typical rapid thermal annealing steps at 750 °C (non-ohmic behaviour) and 850 °C (ohmic behaviour) the intermetallic phases at the metal-semiconductor interface are presented. Increased annealing leads to the transformation of an Al2Au-AlAuTi phase mixture to a mixture of Al2Au-Al3Au8 phases and the formation of Ti-Al-nitride layers at the interfaces. In light of these results the electrical contact properties are discussed. PY - 2002 DO - https://doi.org/10.1088/0268-1242/17/3/312 SN - 0268-1242 SN - 1361-6641 VL - 17 IS - 3 SP - 249 EP - 254 PB - IOP Publ. CY - Bristol AN - OPUS4-1380 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Li, Pengxi A1 - Nolze, Gert T1 - Influence of surface finishing on residual stress depth profiles of a coarse-grained nickel-base superalloy JF - Materials science and engineering A N2 - Residual stress depth profiles of a cast nickel-base superalloy were measured by regarding the deflections occurring in plate-shaped specimens while successively removing layers from the machined or treated surface by electropolishing. The results are in good agreement with previous findings showing (i) the influence of grinding parameters on the width of so-called white layers, which correspond to steep gradients of residual tensile stress, and (ii) a broad zone of compressive residual stress in the case of shot peening. KW - Superalloy KW - Residual stress KW - Grinding KW - Shot peening PY - 1999 SN - 0921-5093 SN - 1873-4936 VL - 262 IS - 1-2 SP - 308 EP - 311 PB - Elsevier CY - Amsterdam AN - OPUS4-13977 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -