Browsing by Author "Kopnarski, Michael"

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    Chemical Bonded PA66-PTFE-Oil Composites as Novel Tribologically Effective Materials: Part 2
    (London [u.a.] : Institute of Physics, 2021) Nguyen, Thanh-Duong; Kamga, Lionel Simo; Gedan-Smolka, Michaela; Sauer, Bernd; Emrich, Stefan; Kopnarski, Michael; Voit, Brigitte; Karjust, Krist; Otto, Tauno; Kübarsepp, Jakob; Hussainova, Irina
    Polytetrafluoroethylene (PTFE) exhibits excellent non-stick properties and a very low coefficient of friction under tribological stress, but it is incompatible with almost all other polymers. In the first part of this study we presented the generation of the novel tribological material based on unsaturated oil, radiation-modified PTFE (MP1100) and Polyamide 66 (PA66). To get a better understanding of the chemical properties and chemical composition of the compounds, the PA66-MP1100-oil-cb (chemical bonded) compounds were examined by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). In this part, the mechanical properties of the compounds are compared with plain PA66 and PA66-MP1100-cb. The tribological investigation was carried out using the Block-on-Ring tribometer. It was found that the mechanical properties of PA66-MP1100-oil-cb with 20 wt.% MP1100-oil-cb only show slight differences compared to PA66, but the tribological properties of the compounds have been significantly improved through chemical coupling between the three components. Finally, the amount of the compound that was deposited on the surface of the steel disc counterpart was analyzed after the tribological testing.
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    Surface softening in metal-ceramic sliding contacts: An experimental and numerical investigation
    (Washington D.C. : American Chemical Society, 2015) Stoyanov, Pantcho; Merz, Rolf; Romero, Pedro A.; Wählisch, Felix C.; Torrents Abad, Oscar; Gralla, Robert; Stemmer, Priska; Kopnarski, Michael; Moseler, Michael; Bennewitz, Roland; Dienwiebel, Martin
    This study investigates the tribolayer properties at the interface of ceramic/metal (i.e., WC/W) sliding contacts using various experimental approaches and classical atomistic simulations. Experimentally, nanoindentation and micropillar compression tests, as well as adhesion mapping by means of atomic force microscopy, are used to evaluate the strength of tungsten?carbon tribolayers. To capture the influence of environmental conditions, a detailed chemical and structural analysis is performed on the worn surfaces by means of XPS mapping and depth profiling along with transmission electron microscopy of the debris particles. Experimentally, the results indicate a decrease in hardness and modulus of the worn surface compared to the unworn one. Atomistic simulations of nanoindentation on deformed and undeformed specimens are used to probe the strength of the WC tribolayer and despite the fact that the simulations do not include oxygen, the simulations correlate well with the experiments on deformed and undeformed surfaces, where the difference in behavior is attributed to the bonding and structural differences of amorphous and crystalline W-C. Adhesion mapping indicates a decrease in surface adhesion, which based on chemical analysis is attributed to surface passivation.