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Stepping piezoelectric actuators based on the stick-slip effect inherently make use of a friction contact between strator and rotor. This contact defines not only the actuator's performance but also is prone to wear and tear. For broad use, the actuator has to be able to perform around 1 million strokes. To assess the actuator's performance in terms of force, speed, mechanical output, electrical input, and long-term stability under different load- and environmental conditions, as well as different friction partners, a dedicated test-bed for a LSPA30µXS motor by Cedrat Technologies has been set up.
A new method for sampling wear particles directly from the lubricant reservoir has been developed and applied successfully for analyzing wear particles by high-resolution scanning electron microscopy in transmission mode having coupled energy-dispersive X-ray spectroscopy. The lubricated tribological testing was carried out with fully formulated as well as with non-formulated synthetic base oil. It was possible to analyze individual particles with dimensions as small as about 5–30 nm which are likely the 'primary' wear particles. A majority of the particles, however, are agglomerated and, thus, lead to the formation of larger agglomerates of up to a few micrometers. Chemical analysis led to the conclusion that most of the observed particles generated in formulated oil, especially the larger ones, are composed of the additives of the lubricant oil. In non-formulated base oil, the primary particles are of similar dimensions but contain only iron, chromium and oxygen, but most likely stem from the mating materials. This finding points to the fact that the main wear mechanism under lubricated conditions with fully formulated oil is more like a continuous shearing process rather than a catastrophic failure with the generation of larger primary particles. When the oil is non-formulated, however, several wear mechanisms act simultaneously and the wear rate is increased significantly. Generated larger primary particles are milled down to the nanoscale. When the oil is fully formulated, wear mainly takes places at the additive layer or tribofilm; thus, the steel surface is protected.
Tribological studies on neat polyetherketone (PEK) and glass fiber reinforced PEK composite were carried out at room and elevated temperature (120 °C). The objective of this study was to characterize for friction and wear properties under dry reciprocating sliding condition at different experimental conditions. The polymer specimens were made to oscillate against steel cylinder as a counterpart. This kind of contact condition are frequently found in bushes, sliding bearing, electronic parts, seals, etc. The friction and wear behavior of neat PEK and composite was quite different at room temperature and elevated temperature. It was observed that glass fiber reinforcement is beneficial in controlling the wear of PEK matrix at room temperature than at elevated temperature. The test results are discussed by considering the surface properties i.e. material removal and film transfer formation. Scanning electron micrographs and optical micrographs of the worn polymer and steel cylinder was used to study the wear mechanisms.
The topography of wear scars on the surface of a steel disc coated with a diamond-like carbon (DLC) layer has been investigated with an Atomic Force Microscope (AFM). AFM topography images have been combined together taking advantage of the stitching technique for the study of wear scars in their initial stage. Moreover, the topography of the sample has been acquired before and after the sliding tests. In this way even very small changes of the sample surface (<10 nm) can be detected. Three main phenomena taking place at the very initial stage of wear could be identified: the abrasion of small asperities bulging out of the sample surface, the carving of swallow grooves with depth under 20 nm, and the partial or total closure of cavities present on the surface. This last phenomenon shows that, before the carving of a wear scar, the plastic deformation of particular regions of the sample, i.e. the volume around the cavities, takes place already after few cycles (in this case between 400 and 800) in the initial phase of the sliding test.
In this article we demonstrate the use of atomic force microscopy (AFM) measurements for the study of macroscopic wear scars. By stitching AFM images acquired over the wear scar, the detailed structure of the scar can be characterized even when the scar is much wider than the typical maximum scan range of the AFM (50–100 µm). The results obtained by AFM are compared with those yielded by white light interferometry (WLI). The comparison validates the WLI measurements; at the same time, it shows decisive differences in the resolutions of these two methods. As a consequence, AFM measurements are necessary whenever a precise characterization of the structure of the scar is required. However, since stitching of AFM images is rather time-consuming, white light interferometry is recommended as a faster method whenever experiments are aimed at just a gross characterization of the scar and the measurement of mean quantities (e.g. the wear volume).
The manufacturing of NbC with Ni binder with addition of titanium carbide by using a colloidal process for blending the different powders without a milling step were investigated. The the sintering process and formation of the resulting microstructures, the phase relations and the hardness of the produced cermet materials are characterized.
Niobium carbide is a ceramic material which can be used with excellent results to replace tungsten carbide with cobalt binder. Furthermore, it might be manufactured by classic ceramic technologies and even colloidal processing. To achieve high toughness and strength, it is necessary to have a perfect mix of hard phase and binder, which is mainly achieved by ball milling. Mechanical and physical properties as well as results on different tribological and application-oriented machining tests are presented. The results have been compared with results obtained with NbC grades with Co and Fe3Al binders as well as with pure binderless hot-pressed NbC and SPS sintered Nb2O5.