Charakterisierung des tribologischen Verhaltens von keramischen Gleitpaarungen mit moderner Oberflächenanalytik

Characterization of the Tribological Behaviour of Ceramic Sliding Couples with Modern Surface Analysis Methods Dry friction and wear tests were performed in ambient atmosphere with various self-mated couples of SiC, Al₂O₃, Si₃N₄ and ZrO₂. The temperature was varied between 22 °C and 1000 °C and the sliding velocity between 0.03 m/s and 5 m/s. Normal force, temperature and sliding velocity are kept constant during the tests. The materials and wear mechanisms were characterized by various surface analytic methods – optical microscopy, scanning electron microscopy, transmission electron microscopy, electron microprobe analysis, IR-spectroscopy, X-ray diffraction, auger electron spectroscopy and X-ray photoelectron spectroscopy. High wear/low wear transitions could be explained. On the basis of these results new ceramic materials with lower friction and/or wear were selected or successful developed.     

Charakterisierung des strukturviskosen Verhaltens von Schmierstoffen durch Kombination von Experiment und EHD-Simulation mithilfe des Carreau-Modells

In the present work, the fluid friction in the gap between two discs was examined under full fluid film lubrication conditions. The investigation was both experimental and simulative, whereby input variables for the simulative investigation were obtained from the experimental test series. The experimental examination of fluid friction was carried out on the MEGT’s twin-disk-machine, whereby the load and slide-to-roll-ratio were varied at constant hydrodynamic velocity and oil inlet temperature. The reference oil FVA-3 was used as lubricant. As a result of the experimental investigation, traction curves are obtained which show the change in the coefficient of friction or the shear stress as a function of the slide-to-roll-ratio. The maximum and critical shear stress can be determined from the measured traction curves. These represent input variables for the simulative determination of friction in the gap.     

Untersuchung des tribologisch‐mechanischen Verhaltens amorpher Kohlenstoffschichten mittels Load Scanner

Amorphous carbon coatings have a beneficial tribological behaviour since they provide low friction even under dry sliding conditions and at the same time they offer a good wear protection. Under high loads, the applicability of state‐of‐the‐art amorphous carbon coatings is limited by mechanical failure. However, there is still little knowledge concerning the precise failure mechanisms under application‐oriented conditions. In the present study, cylindrical specimens of a cold work tool steel were coated with two commercial amorphous carbon coating systems: a WCC coating with an a‐C:H:W top layer and a DLC coating which architecture is based on that of the WCC coating, but contains an additional a‐C:H top layer. The coated specimens were tested on a load‐scanning test rig in dry sliding contact against uncoated specimens of the same steel substrate. In the tests, the specimens were loaded with a normal force in the range of 13 and 350 N, corresponding to a maximum contact pressure of 1 to 3 GPa. The number of load cycles was varied between 1 and 60. Firstly, the load‐dependent friction behaviour was monitored. Secondly, the tests were stopped at different total cycle numbers allowing for an evaluation of the progress of wear and damage by scanning electron microscopy. For both coating systems, adhesive pick‐up of counter body steel was observed prior to mechanical failure. Whilst the WCC coating system showed first indications of local failure after several load cycles and at contact pressures exceeding 2 GPa, the DLC coating system showed catastrophic failure on a global scale only after few load cycles and over the whole investigated load range.     

Charakterisierung von Glas und Glasbeschichtung mittels oberflächensensibler Sondenverfahren

The presented results of investigations by surface and microanalytical methods confirm the suitability of electron beam and scanning probe techniques for process monitoring, support of process development and defect analyses in the glass industry. More and more glass and coating specialists use the high tech service provided by an external laboratory with its wide range of experience and knowledge.     

Schweißen von Hohlstrukturen und offenporösen Metallschäumen für den Einsatz in Kombi‐Kraftwerken

Welding of Hollow Structures and Open‐Porous Metal Foams for Application in Combined Cycle Power Plants For applications within the scope of novel cooling concepts joining technologies for sandwich composites and open‐porous metal foams are researched in the context of the Collaborative Research Centre 561 “Thermally highly loaded, porous and cooled multi‐layer systems for combined cycle power plants”. The research motivation and application fields of the different structures are defined. Welding processes and strategies for manufacturing these structures are specified as well as the joining technologies’ characteristics. Planned future works for enhancements of the processes and structures are listed.     

Charakterisierung von Plasmapolymeren mittels Thermolumineszenzmessungen

Characterization of Plasmapolymers by Thermoluminescence Thin plasma polymer films were deposited using the pulsed plasma (pp) mode. These plasma polymers should possess a more chemically regular structure because of the lower monomer fragmentation during the short plasma pulses and the chemical chain propagation during the plasma‐less periods than those produced by the conventional continuous‐wave (cw) mode. In addition to the use of the classic thin film characterization method XPS the method of thermoluminescence was applied to characterize defects and structural specifics in the polymer films produced by pp or cw‐plasma mode. The thermoluminescence method was applied to functional groups‐carrying plasma polymer layers, which are used in medical technology for forming biocompatible and bioactive coatings or in metal‐polymer composites as adhesion‐promoting interlayers.     

Experimentelle und analytische Untersuchung des out‐of‐plane‐Verhaltens von unbewehrten Mauerwerkswänden unter Erdbebenbelastung

Experimental and analytical investigation of the seismic out‐of‐plane behavior of unreinforced masonry walls In addition to the vertical and horizontal load‐bearing in‐plane, masonry must also withstand out‐of‐plane loads that occur in earthquake scenarios. The out‐of‐plane behavior of unreinforced masonry walls depends on a variety of parameters and is very complex due to the strong non‐linearity. Current design methods in German codes and various international codes have not been explicitly developed for out‐of‐plane behavior and contain considerable conservatism. In the present work, shaking‐table experiments with heat‐insulating masonry walls have been conducted to investigate the out‐of‐plane behavior of vertical spanning unreinforced masonry walls. As shown in previous numerical investigations, important parameters are neglected in existing design and analysis models and the out‐of‐plane capacity is underestimated significantly. In the conducted experiments the results of these numerical investigations are verified. Furthermore, the development of an analytical design model to determine the force‐displacement relationship and the out‐of‐plane load‐bearing capacity considering all significant parameters is presented.     

Untersuchung des Erosionsverhaltens von silberbasierten Kontaktwerkstoffen mittels FIB‐Techniken

Microstructure investigations and arc erosion behaviour of silver‐based contact materials by focused ion beam technique The understanding of the degradation mechanisms of contact materials is a key issue for the development of new materials with enhanced durability. This can be achieved through the investigation of the microstructure modification caused by electrical arcs on the surface of contacts. In this work, the erosion behaviour of pure silver and silver based composites as well as the characterization in two or three dimensions is presented. Single breaking operations were performed with direct current. Using white light interferometry, the size of the craters on the surface as well as the volume of eroded material has been measured. By means of dual beam techniques, the microstructural modifications in the crater have been investigated and reconstructed in three dimensions.     

Charakterisierung plasma‐ modifizierter Polymere mittels SSXPS und XPS‐Imaging

For many years now, engineering polymers with tailor‐made surface properties are of widespread interest. One of the most commonly used technique to functionalize or coat polymers is the plasma technique. One of the most important reasons is the possibility to tailor the surface properties without alteration of the versatile bulk properties. Many engineering polymers applied in medical equipment, life‐science, and biotechnological purposes demand monofunctionalized and structured surfaces. Those can be obtained with appropriate process parameters. The characterization of such tailored surfaces as well as of surfaces with structured functionality can be performed by several analytical tech niques. Besides AFM and FTIR the photoelectron spectroscopy (XPS, ESCA) is used.