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- Fretting (7)
- Wear (6)
- Friction (4)
- Contact pressure (3)
- Reibung (3)
- Roughness (3)
- Temperature (3)
- Wires (3)
- Atomic force microscopy (2)
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Main focus was on the correlation of the coefficient of friction (COF) with the geometrical parameters of the surface during early stage of the running-in period. TiN, TiAlN and AlTiN coatings were prepared by using rotating cathode arc evaporation unit. The roughness of the WC-Co substrate Ra ranged from 0.05 to 0.2 µm and the coating thickness was 2.3 ± 0.2 µm. Part of the samples were subjected to the surface modification by the drag grinding finishing. Geometrical parameters of the surface were evaluated by means of atomic force microscopy (AFM) and fretting tests were conducted with 10 mm diameter alumina ball under 2 N load, 100 µm slip distance and the frequency of 10 Hz. It was found that the distribution of macroparticles strongly influences the geometrical parameters of the surface and the number of macroparticles increases with increasing Al content in the coating. In the case of the positive skewness Ssq of the coating surface, the kurtosis Sku provides a statistically significant effect on the COF, namely the COF depends inversely on the kurtosis Sku. The kurtosis value for TiN was the highest among as-deposited coatings, subsequently, the slowest increase rate in the COF was observed for the TiN coating.
Im Vortrag wird neben der apparativen Prüftechnik das allgemeine methodische Vorgehen für Modell-Verschleißuntersuchungen im Bereich des partial slip vorgestellt. Im Detail wird für Dental-Implantat-Werkstoffe eine Rangfolge aufgestellt, die vergleichend die Verschleißresistenz unterschiedlicher Ti-basierter Werkstoffe zeigt. Wird durch die Kaubewegung eine mehrachsige Beanspruchung in die Kontaktflächen der Schraubverbindung eingeleitet, kann durch partial slip im Randbereich dieser Kontaktfläche ein Verschleißprozess initiiert werden, der die Lockerung des Implantats begünstigt. Eine gute Verschleißresistenz verhindert oder schiebt die vorzeitige Lockerung hinaus.
Um das Werkstoffverhalten in Bezug auf eine vorzeitige Lockerung der Implantatkrone bei geschraubten zweiteiligen Implantaten zu charakterisieren, wurden zylindrische Probekörper unter partial slip Fretting-Bedingungen mit Zyklenzahlen bis n = 200 000 beansprucht. Die Frequenz der aufgebrachten Tangentialkraft betrug 2 Hz, um die Kaubewegung zu simulieren.
Die tribologischen Untersuchungen wurden auf einem Eigenbau-Tribometer mit der Kontaktgeometrie „gekreuzte Zylinder“ durchgeführt. Die zylindrischen Proben wurden aus den Werkstoffen Titan Grade 4 und der Ti-Legierung Ti6AI4V gefertigt. Ein Teil dieser Ti-basierten Proben wurde oberflächengehärtet. Die bisher erzielten Ergebnisse zeigen, dass die oberflächenbehandelten Proben dazu neigen, unter der Belastung die Kontaktfläche zu vergrößern. Dies deutet auf einen Effekt bekannt als „junction growth“ und damit auf eine erhöhte Versetzungsbeweglichkeit der randschichtgehärteten Proben hin. Einen Einfluss der Zwischenstoffe konnte nicht nachgewiesen werden.
After having checked in a previous study the influence of stroke and normal load in laboratory fretting tests accomplished with thin steel roping wires, in this paper the effect of the contact pressure (test configuration), environmental conditions (relative humidity) and reduction of the friction coefficient (lubricants) on the wear behaviour were analysed. The wires were 0.45 mm in diameter and the material was a cold-drawn eutectoid carbon steel (0.8% C) with a Tensile Strength over 2800 MPa. The tests were performed on an oscillating test rig and the volumetric wear of both specimens of the tribocouple was determined separately from three-dimensional topographies of the wear scars acquired by means of a confocal profiler, and a calculation algorithm developed in using MATLAB®. The strong effect of humidity and lubrication on wear behaviour was proved, whereas a slight effect of contact pressure was derived.
The tribological performance of a hydrogenated amorphous carbon coating on Ti6Al4V against ceramic balls was checked by simple reciprocating sliding tests and by more complicated tests in a hip joint simulator. 3 of 4 joints failed during hip simulator testing already after approximately 100 × 10³ cycles and possibly due to coating failures caused by insufficient polishing of the metallic acetabular cups prior to coating deposition. Since such failures occurred only occasionally, the problem was not revealed by reciprocating sliding tests which are stressing a much smaller surface area compared to the tests in the hip joint simulator. Another type of failure, pits of 12 µm in diameter distributed randomly at the coating surface, was frequently observed by Scanning Electron Microscopy and analyzed comprehensively by Focused Ion Beam technique in combination with Transmission Electron Microscopy in one case. Although not necessarily affecting wear, such small failures might cause long-term problems in vivo, by providing access of body fluid to the substratecoating interface making it susceptible to corrosion.