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Ausgegangen wird von der Vorstellung, dass die Anwendung der Kontinuumsmechanik auf polykristalline Werkstoffproben als Ganzes nicht der Natur der Schädigungsvorgänge bei der Werkstoffzerrüttung gerecht werden kann. Die Aufmerksamkeit muss sich vielmehr auf das Verhalten der einzelnen Kristalle richten.
Verformungstopographien metallischer Werkstoffproben, die durch Werkstoffzerrüttung entstanden sind, können mit einer speziellen Wechselbiegeapparatur sowohl außerhalb als auch innerhalb des Objektraumes eines Rasterelektronenmikroskops untersucht werden, wobei die Arbeit den spezifischen Verformungstopographien gilt.
Die kontinuumsmechanische Erfassung des zeitlichen Ablaufs der elastisch- plastischen Dehnungen bei der Zerrüttung Ausgangspunkt ist das Ziel, die Möglichkeiten der Anwendung kontinuumsmechanischer Formulierungen auf den Problemkreis die Zerrüttung zu untersuchen, um Aussagen über die ertragbaren zyklisch-dynamischen Beanspruchungen von Werkstoffen zu gewinnen.
Tribologische Charakterisierung von Werkstoffen bei ungeschmierter reversierender Gleitbewegung
(1996)
Ceramics are of increasing interest for application in many branches of technique. In order to improve the tribological performance of ceramic materials, composites on the basis of silicon carbide with different amounts of titanium carbide, boron carbide, titanium diboride and free carbon in the form of graphite were manufactured by a reaction sintering process.
The friction and wear behaviour of these composites was investigated with oscillating sliding motion in unlubricated tests at room temperature on different levels of relative humidity. Additional tests were performed under water lubrication, revealing the superior behaviour of composites for special test conditions. A major influence of the free carbon on friction or wear behaviour was not observed. The tribological behaviour in air as well as under water is mainly dependant on the amount of titanium phases.
The friction and wear behaviour of thin hard coatings, such as TiN and the promising class of C-based coatings (a-C, a-C:H, and diamond for example), are compared under oscillating and reciprocating sliding conditions. The typical effects of test parameters, such as stroke, frequency, normal force, relative humidity and test duration, are described as a basis for the proper selection of test conditions or, conversely, for the selection of suitable coatings for particular practical applications.
Friction and wear data from over 1000 vibrating tests using thin hard coatings against 100Cr6 and against Al2O3 have been compiled in a database. This allows easy manipulation and comparison of test results. Using selection criteria and filter procedures (e. g., lifetime of coatings, friction limits, and critical wear rate), suitable coating systems for different test conditions can be chosen from the database. The effects of test parameters on friction and wear behaviour and changes have anyway to be known for meaningful tribotesting, as well as for the selection of coatings.
The friction and wear behaviour of materials is often characterised in laboratory tests using a simple ball-on-flat configuration. From this type of test can be derived information useful in guiding the development of tribomaterials and in helping select candidate materials for specific applications. A large variety of tribotesting methods exists, and indeed several are not yet standardised. One of these methods is the oscillating sliding test, where a ball moves in relation to a disc, usually with small strokes. This method is almost non-destructive and can be applied to very small specimens. One of the most important parameters in laboratory tests is the humidity of the surrounding air. Experimental results on the friction and wear characteristics of different ceramics tested against different ball materials at room temperature in oscillating sliding contact are presented here and discussed, taking into account the effects of the test duration, relative humidity, and counterbody material.
Polycrystalline diamond layers were deposited onto the titanium alloy Ti6Al4V via microwave plasma chemical vapor deposition (CVD). It is shown that the diamond film reduces wear and friction immensely compared with uncoated titanium/titanium tribo systems. An additional polishing process of the CVD-diamond layer improves the wear behavior even further. An influence of air humidity is found.
In addition, different ceramic materials (Al2O3, SiC, Si3N4, ZrO2) were tested against as-deposited and polished CVD-diamond layers. Al2O3 and Si3N4 exhibit very good wear behavior accompanied by very low friction against as-deposited CVD-diamond. SiC and ZrO2, however, show somewhat inferior wear and friction behavior. Suggestions are made to explain the different performance. Again, a wear increase is found with increasing humidity. Polishing of CVD-diamond layers improves the tribological performance further.