Browsing by Author "Merle, Benoit"

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    Combining multi-scale surface texturing and DLC coatings for improved tribological performance of 3D printed polymers
    (2023) Marian, Max; Zambrano, Dario F.; Rothammer, Benedict; Waltenberger, Valentin; Boidi, Guido; Krapf, Anna; Merle, Benoit; Stampfl, Jürgen; Rosenkranz, Andreas; Gachot, Carsten; Grützmacher, Philipp G.
    Polymer components fabricated by additive manufacturing typically show only moderate strength and low temperature stability, possibly leading to severe wear and short lifetimes especially under dry tribological sliding. To tackle these shortcomings, we investigated the combination of single- and multi-scale textures directly fabricated by digital light processing with amorphous diamond-like carbon (DLC) coatings. The topography of the samples and conformity of the coatings on the textures are assessed and their tribological behaviour under dry conditions is studied. We demonstrate that the surface textures have a detrimental tribological effect on the uncoated samples. This changes with the application of DLC coatings since friction substantially reduces and wear of the textures is not observed anymore. These trends are attributed to the protection of the underlying polymer substrate by the coatings and a reduced contact area. The best tribological performance is found for a coating with highest hardness and hardness-to-elasticity ratios. Moreover, multi-scale textures perform slightly better than single-scale textures due to a smaller real contact area. Summarizing, we verified that the high flexibility and low production costs of 3D printing combined with the excellent mechanical and tribological properties of DLC results in synergistic effects with an excellent performance under dry sliding conditions
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    Evaluation of the surface fatigue behavior of amorphous carbon coatings through cyclic nanoindentation
    (2021) Weikert, Tim; Wartzack, Sandro; Baloglu, Maximiliano V.; Willner, Kai; Gabel, Stefan; Merle, Benoit; Pineda, Fabiola; Walczak, Magdalena; Marian, Max; Rosenkranz, Andreas; Tremmel, Stephan
    Diamond-like carbon (DLC) coatings, frequently used to reduce wear and friction in machine components as well as on forming tools, are often subjected to cyclic loading. Doping of DLC coatings with metals or metal carbides as well as the usage of multilayer architectures represent promising approaches to enhance toughness, which is beneficial for the coatings' behavior under cyclic loading. In this study, we utilized cyclic nanoindentation to characterize the tribologically induced surface fatigue behavior of single-layer tungsten-doped (a-C:H:W) and multilayer silicon oxide containing (a-C:H:Si:O/a-C:H)25 amorphous carbon coatings under cyclic loading. Columnar growth was observed for both coatings by focused ion beam microscopy and scanning electron microscopy, while the multilayer architecture of the (a-C:H:Si:O/a-C:H)25 coating was verified by the silicon content using glow-discharge optical emission spectroscopy. In cyclic nanoindentation of the (a-C:H:Si:O/a-C:H)25 multilayer coating, stepwise small changes in indentation depth were observed over several indentation cycles. The surface fatigue process of the single-layer a-C:H:W covered a smaller number of indentation cycles and was characterized by an early steep increase of the static displacement signal. Microscopical analyses hint at grain deformation, sliding at columnar boundaries, and grain detachment as underlying fatigue mechanisms of the a-C:H:W coating, while the (a-C:H:Si:O/a-C:H)25 multilayer coating showed transgranular crack propagation and gradual fracturing. In case of the (a-C:H:Si:O/a-C:H)25 multilayer coating, superior indentation hardness (HIT) and indentation modulus (EIT) as well as a higher HIT3/EIT2 ratio suggest a higher resistance to plastic deformation. A high HIT3/EIT2 ratio, being an indicator for hindered crack initiation, combined with the capability of stress relaxation in soft layers contributed to the favorable surface fatigue behavior of the (a-C:H:Si:O/a-C:H)25 multilayer coating observed in this cyclic nanoindentation studies
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    Wear Mechanism of Superhard Tetrahedral Amorphous Carbon (ta-C) Coatings for Biomedical Applications
    (2023) Rothammer, Benedict; Schwendner, Michael; Bartz, Marcel; Wartzack, Sandro; Boehm, Thomas; Krauss, Sebastian; Merle, Benoit; Schroeder, Stefan; Uhler, Maximilian; Kretzer, Jan Philippe; Weihnacht, Volker; Marian, Max
    Tetrahedral amorphous carbon (ta-C) coatings have the potential to protect biomedical implants from wear and increase their service life. This study elucidates the biocompatibility, mechanical properties, adhesion, and wear resistance of ta-C coatings fabricated by physical vapor deposition on cobalt-chromium-molybdenum (CoCr) and titanium (Ti64) alloys as well as ultrahigh molecular weight polyethylene (UHMWPE). Satisfactory cytocompatibility is verified using contact angle and surface tension measurements as well as indirect and direct cell testing. Scratch testing demonstrates excellent adhesion to the substrates and as confirmed by nanoindentation, the coatings represent an up to 13-fold and 182-fold increase in hardness on the hard and soft materials. In metal pin-on-UHMWPE disk sliding experiments under simulated body fluid lubrication, the wear rates of the disk are reduced by 48% (against CoCr) and 73% (against Ti64) while the pin wear rates are reduced by factors of 20 (CoCr) and 116 (Ti64) compared to uncoated pairings. From optical and laser scanning microscopy, Raman measurements, and particle analyses, it is shown that the underlying substrates remain well protected. Nonetheless, focused ion beam scanning electron microscopy revealed coating process-related and thermally driven subductions as well as tribologically induced near-surface fatigue, which can potentially constitute critical wear mechanisms.