TY - JOUR A1 - Dmitriev, A. I. A1 - Häusler, Ines A1 - Wetzel, B. A1 - Zhang, G. A1 - Österle, Werner T1 - Modeling of the stress-strain behavior of an epoxy-based nanocomposite filled with silica nanoparticles N2 - The method of movable cellular automata (MCA) was applied to simulate the stress-strain behavior of a nano composite consisting of an epoxy matrix and 6 vol. % silica nano particles. The size of the elements used for modelling was fixed at 10 nm, corresponding approximately to the diameter of the filler particles. Since not only the stress-strain response of the two constituents but also debonding of neighboring particles and granular flow was taken into account, plastic deformation as well as crack initiation and propagation could be simulated with the model. Modelling results were compared with tensile test results of both, pure epoxy as well as the epoxy-6 vol. % SiO2 composite. Since assuming bulk properties of the two constituents did not yield satisfactory results, slight modifications of the nanoparticle response functions and nanostructures were tested numerically. Finally, it was observed that only the assumption of slightly increased strength properties of the epoxy yielded good correlation between experimental and modelling results. This was attributed to an increased cross linking of the epoxy caused by the presence of silica nano particles. KW - Nanocomposite KW - Polymer matrix composite KW - Stress-strain behavior KW - Modeling KW - Computational mechanics PY - 2016 DO - https://doi.org/http://dx.doi.org/10.1016/j.matdes.2015.10.038 SN - 0264-1275 VL - 89 SP - 950 EP - 956 PB - Elsevier AN - OPUS4-35596 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Dmitriev, A. I. A1 - Wetzel, B. A1 - Zhang, G. A1 - Häusler, Ines A1 - Jim, B.C. T1 - The role of carbon fibers and silica nanoparticles on friction and wear reduction of an advanced polymer matrix composite N2 - Excellent tribological properties of an advanced polymer matrix composite were obtained by a combination of micro- and nano-sized fillers. Surface features and the nanostructure of tribofilms were characterized by advanced microscopic techniques, and correlated with the macroscopic behavior in terms of wear rate and friction evolution. A model based on movable cellular automata was applied for obtaining a better understanding of the sliding behavior of the nanostructured tribofilms. The failure of the conventional composite without silica nanoparticles could be attributed to severe oxidational wear after degradation of an initially formed polymer transfer film. The hybrid composite preserves its antiwear and antifriction properties because flash temperatures at micron-sized carbon fibers, lead to polymer degradation and subsequent release of nanoparticles. It has been shown that the released particles are mixed with other wear products and form stable films at the disc surface thus preventing further severe oxidational wear. Furthermore, the released wear product also is embedding carbon fibers at the composite surface thus preventing fiber fragmentation and subsequent third body abrasion. With nanoscale modelling we were able to show that low friction and wear can be expected if the nanostructured silica films contain at least 10 vol.% of a soft ingredient. KW - Carbon fibers KW - Silica nanoparticles KW - Hybrid composite KW - Tribological properties KW - Tribofilm KW - Sliding simulation PY - 2016 DO - https://doi.org/10.1016/j.matdes.2015.12.175 SN - 0264-1275 VL - 93 SP - 474 EP - 484 PB - Elsevier AN - OPUS4-35598 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, G. A1 - Wetzel, B. A1 - Jim, B. A1 - Österle, Werner T1 - Impact of counterface topography on the formation mechanisms of nanostructured tribofilm of PEEK hybrid nanocomposites N2 - The effect of steel counterface topography on the formation mechanisms of nanostructured tribofilms of polyetheretherketone (PEEK) hybrid nanocomposites was studied. Three types of surface finishes with mean roughness Ra ranging from nano- to micro-scale were investigated. Tribo-sintering of nanopartides, oxidation of counterface steel and compaction of wear debris are identified to be competing factors dominating the formation and function of the tribofilms. Counterface topography played an important role on the competing factors, and thereby influenced significantly the final structure, the load-carrying capability and the lubrication performance of the tribofilms. It was disclosed that a thin tribofilm, which mainly consists of silica nanoparticles and which forms on the counterface with a submicron roughness, benefits best the tribological performance of the composites KW - Surface topography KW - Nanocomposite KW - Tribology KW - Tribofilm PY - 2015 DO - https://doi.org/10.1016/j.triboint.2014.11.015 SN - 0301-679X VL - 83 SP - 156 EP - 165 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-34612 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pontes Rodrigues, A. C. A1 - Nunes Ribeiro, P. J. A1 - Österle, Werner A1 - de Farias Azevedo, C. R. T1 - Failure analysis as a tool to optimize the design of a ring on disc tribotest investigating the role of surface roughness N2 - The influence of the surface roughness of pearlitic grey cast iron discs on the formation of tribofilms and the evolution of the friction coefficient during a ring on disc tribotest with the addition of magnetite and magnetite–graphite nanopowders as interfacial media was investigated. The roughness parameters of the cast iron discs were varied by electro discharge machining (EDM) and grinding processes, producing four distinct surface roughness conditions. The evolution of the friction coefficient, however, did not reach the steady state for most of the samples and the role of the surface roughness on the friction coefficient could not be identified. Focused ion beam (FIB) microscopy on the cast iron discs was carried out to investigate the microstructure of the discs near the tribosurface. These results showed that the EDM process not only varied the surface roughness, but also changed the microstructure of the cast iron discs, promoting the incipient fusion of the cast iron surface, with the formation of ridges and casting defects (pores). As a result, a layer of rapidly solidified metal with a dendritic microstructure was formed near to the surface of the EDMed discs. KW - Ring-on disc tribotest KW - Surface roughness KW - EDM-processing KW - Rapid solification PY - 2015 DO - https://doi.org/10.1016/j.engfailanal.2015.03.011 SN - 1350-6307 SN - 1873-1961 VL - 56 SP - 131 EP - 141 PB - Elsevier Science Publ. CY - Oxford AN - OPUS4-34623 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Wever, H. A1 - Bunge, H. T1 - Development of microstructure and texture of cold rolling α iron PY - 1983 SN - 0026-0681 IS - 17 SP - 333 EP - 340 PB - Maney Publ. CY - London, UK AN - OPUS4-36056 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Giovannozzi, A. A1 - Gradt, Thomas A1 - Häusler, Ines A1 - Rossi, A. A1 - Wetzel, B. A1 - Zhang, G. A1 - Dmitriev, A.I. T1 - Exploring the potential of Raman spectroscopy for the identification of silicone oil residue and wear scar characterization for the assessment of tribofilm functionality N2 - 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. KW - Raman spectroscopy KW - Cross-sectional TEM KW - Silicone oil residue KW - Tribofilm PY - 2015 DO - https://doi.org/10.1016/j.triboint.2015.04.046 SN - 0301-679X VL - 90 SP - 481 EP - 490 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-33421 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner T1 - Berechnung des Streckengrenzbeitrages plättchenförmiger Teilchen auf der Grundlage einer quantitativen Gefügeanalyse mit dem TEM PY - 1984 SN - 0032-678X VL - 21 SP - 377 EP - 389 PB - Hanser CY - München AN - OPUS4-36601 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bettge, Dirk A1 - Österle, Werner T1 - “Cube slip” in near-[111] oriented specimens of a single-crystal nickel-base superalloy N2 - In the past few years, it has been discussed with increasing frequency, whether cube slip does occur in gamma' hardened nickel-base superalloys. Occurrence of cube slip has consequences for the modeling of orientation dependence of the CRSS. Until now, there are only few experimental investigations. In principle, cube slip should be possible in primitive cubic lattices (e.g. L12 ordered gamma' phase) but not in face centered cubic ones (e.g. Ni solid solution). The most favourable specimen orientations are near [111], where the Schmid factors for this type of glide exceed those for octahedral systems. There are two basic methods to detect cube slip: macroscopic slip trace analysis and Transmission electron microscopy (TEM) investigation of the dislocation structure. Few observations of cube slip by macroscopic slip traces are reported in the literature. But it is still uncertain under which test conditions cube slip occurs and what the dislocation mechanisms are. Cube slip was observed during tensile or compression tests of several first generation superalloys, but it seems not to occur during shear creep deformation (e.g. CMSX-4 at 980°C), and it is also lacking under conventional tensile or compression loading, if the gmma' particles are small. No observations were ever reported of dislocations gliding on {001} planes in matrix channels. KW - Cube slip KW - Nickel-base superalloy KW - Dislocations KW - TEM PY - 1999 DO - https://doi.org/10.1016/S1359-6462(98)00446-1 SN - 1359-6462 VL - 40 IS - 4 SP - 389 EP - 395 PB - Elsevier AN - OPUS4-38220 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhao, F. A1 - Li, G. A1 - Österle, Werner A1 - Häusler, Ines A1 - Zhang, G. A1 - Wang, T. A1 - Wang, Q. T1 - Tribological investigations of glass fiber reinforced epoxy composites under oil lubrication conditions N2 - The tribological performance of short glass fibers (SGF),solid lubricants and silica nanoparticles filled epoxy (EP) composites was investigated under oil lubrication conditions. It is demonstrated that the addition of SGF greatly reduces the friction and wear of EP. However, further addition of solid lubricants and silica nanoparticles does not change obviously the friction and wear. It is identified that the high tribological performance of SGF reinforced EP is related to the high load carrying capacity and abrasion resistance of SGF. The nanostructure of the tribofilm was comprehensively characterized. It is deemed that the tribofilm plays an important role in the tribological performance by avoiding the direct rubbing of the sliding pairs exposed to boundary and mixed lubrication conditions. KW - Reinforced epoxy composites KW - Short glass fiber KW - Oil lubrication KW - Tribofilm PY - 2016 DO - https://doi.org/10.1016/j.triboint.2016.07.002 SN - 0301-679X VL - 103 SP - 208 EP - 217 PB - Elsevier Ltd. AN - OPUS4-38145 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ressel, P. A1 - Österle, Werner A1 - Urban, Ingrid A1 - Klein, A. A1 - Vogel, K. A1 - Kräutle, H. T1 - Transmission electron microscopy study of rapid thermally annealed Pd/Ge contacts on In0.53Ga0.47As N2 - Phase formation in rapid thermally annealed Pd/Ge contacts on In0.53Ga0.47As has been investigated by means of cross-sectional transmission electron microscopy, convergent-beam electron diffraction, and energy-dispersive x-ray analysis. Solid-phase regrowth is observed to occur similarly as in Pd/Ge contacts on GaAs or InP. The reaction starts at low temperatures with the formation of an amorphous Pd–In–Ga–As layer, which crystallizes at elevated temperatures yielding hexagonal Pd4In0.53Ga0.47As being first described in this work. At temperatures .250 °C, this phase decomposes due to epitaxial solid-phase regrowth of In0.53Ga0.47As and formation of Pd–Ge phases. The stable composition is reached at temperatures .350 °C with excess Ge diffused through top Pd–Ge to the contact interface and growing epitaxially on the semiconductor. KW - Semiconductor KW - Thin film contact layer KW - Electron microscopy KW - Intermetallic phases PY - 1996 DO - https://doi.org/10.1063/1.363348 SN - 0021-8979 VL - 80 IS - 7 SP - 3910 EP - 3914 AN - OPUS4-38537 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -