The tribological protection of carbon fiber reinforced epoxy composites (CFC) is essential for broadening their use from structural to functional applications, e.g., to linear bearings in mechanical engineering. However, their wear resistance in sliding and rolling contacts is low. This work focusses on the possibility of improving their tribological properties by the application of thin hard multi-layered coatings. Chromium nitride (CrN) single layer and chromium-CrN multilayer coatings of ~4 µm thickness, partly finished with a 1 µm diamond-like carbon (DLC) top layer, were deposited by magnetron sputtering at low temperatures on soft CFC and for comparison of the mechanical behavior on comparatively hard austenitic steel substrates. Structural investigations showed especially that the multilayer coatings possess a very fine grained, columnar microstructure and a very low density of intercolumnar micro-cracks, while the single layer coatings possess a coarse structure. The indentation testing and the analysis of the deformed and fractured cross-sections revealed a tougher behavior with improved plastic deformability of the multilayers in comparison to CrN single layers. However, in wear testing only coatings with DLC top layers significantly improved the tribological material properties of CFC. This is due to the reduced shear forces in sliding on low-friction DLC coatings on the soft epoxy-based CFC, decreasing the total dynamic stresses during sliding under high loads.

The scope of this work is to provide an overview of the influences of process parameters, print orientation, and post-process treatments of Ti6AlV4 processed by laser powder bed fusion on its microstructure and physical and mechanical properties and their anisotropic behavior. To avoid the influence of changes in powder quality and ensure comparability, experiments were carried out using a single batch of virgin powder. First, characterization of the density and surface roughness was performed to optimize the process parameters utilizing design of experiment. Tensile, notched bar impact and compression test specimens were built in three different orientations: vertically, horizontally, and inclined at 45° to the build plate. Later, the influence of the staircase effect and the possible course of anisotropy from vertical to horizontal were investigated. Subsequently, heat treatments for stress relief, furnace annealing, and hot isostatic pressing were performed. In addition to as-built samples, mechanical machining and a two-step electrochemical polishing surface treatment were applied to investigate the influence of the surface roughness. With parameter optimization, a relative density of 99.8% was achieved, and surface roughness was improved over default parameters, reducing Ra by up to 7 µm. Electrochemical polishing is a viable way to decrease the surface roughness. An Ra value of 1 µm and an Rz value of 4 µm can be achieved for 45° downskin surfaces with as-built surface roughness values of Ra 24 µm and Rz 117 µm. As-built and stress-relieved conditions show little anisotropy in their yield and tensile strength (max 2.7%), but there is a strong influence of the build orientation on necking, and brittle fracture behavior is shown due to the martensitic microstructure (up to 70%). Heat treatment can increase the ductility and further decrease the strength anisotropy with both furnace annealing and hot isostatic pressing delivering similar results for tensile properties, while angled samples exhibit behavior that is closer to vertical than horizontal, indicating a non-linear change in break behavior. Electrochemical polishing increases fracture necking, and its isotropy drastically increases from 4% to over 30% compared with as-built parts, which is close to the level of the machined specimen.

Biocompatibility improvements for blood contacting materials are of increasing interest for implanted devices and interventional tools. The current study focuses on inorganic (titanium, titanium nitride, titanium oxide) as well as diamond-like carbon (DLC) coating materials on polymer surfaces (thermoplastic polyurethane), deposited by magnetron sputtering und pulsed laser deposition at room temperature. DLC was used pure (a-C:H) as well as doped with silicon, titanium, and nitrogen + titanium (a-C:H:Si, a-C:H:Ti, a-C:H:N:Ti). In-vitro testing of the hemocompatibility requires mandatory dynamic test conditions to simulate in-vivo conditions, e.g., realized by a cone-and-plate analyzer. In such tests, titanium- and nitrogen-doped DLC and titanium nitride were found to be optimally anti-thrombotic and better than state-of-the-art polyurethane polymers. This is mainly due to the low tendency to platelet microparticle formation, a high content of remaining platelets in the whole blood after testing and low concentration of platelet activation and aggregation markers. Comparing this result to shear-flow induced cell motility tests with e.g., Dictostelium discoideum cell model organism reveals similar tendencies for the investigated materials.

Protective ultra-thin barrier films gather increasing economic interest for controlling permeation and diffusion from the biological surrounding in implanted sensor and electronic devices in future medicine. Thus, the aim of this work was a benchmarking of the mechanical oxygen permeation barrier, cytocompatibility, and microbiological properties of inorganic ~25 nm thin films, deposited by vacuum deposition techniques on 50 µm thin polyetheretherketone (PEEK) foils. Plasma-activated chemical vapor deposition (direct deposition from an ion source) was applied to deposit pure and nitrogen doped diamond-like carbon films, while physical vapor deposition (magnetron sputtering in pulsed DC mode) was used for the formation of silicon as well as titanium doped diamond-like carbon films. Silicon oxide films were deposited by radio frequency magnetron sputtering. The results indicate a strong influence of nanoporosity on the oxygen transmission rate for all coating types, while the low content of microporosity (particulates, etc.) is shown to be of lesser importance. Due to the low thickness of the foil substrates, being easily bent, the toughness as a measure of tendency to film fracture together with the elasticity index of the thin films influence the oxygen barrier. All investigated coatings are non-pyrogenic, cause no cytotoxic effects and do not influence bacterial growth.

The versatility of sol–gel systems makes them ideal for functional coatings in industry. However, existing coatings are either too thin or take too long to cure. To address these issues, this paper proposes using an atmospheric pressure plasma source to fully cure and functionalize thicker sol–gel coatings in a single step. The study explores coating various substrates with sol–gel layers to make them scratch-resistant, antibacterial, and antiadhesive. Microparticles like copper, zinc, or copper flakes are added to achieve antibacterial effects. The sol–gel system can be sprayed on and quickly functionalized on the substrate. The study focuses on introducing and anchoring particles in the sol–gel layer to achieve an excellent antibacterial effect by changing the penetration depth. Overall, this method offers a more efficient and effective approach to sol–gel coatings for industrial applications. In order to achieve a layer thickness of more than 100 µm, the second part of the study proposes a multilayer system comprising 15 to 30 µm thick monolayers that can be modified by introducing fillers (such as TiO₂) or scratch-resistant chemicals like titanium isopropoxide. This system also allows for individual plasma functionalization of each sol–gel layer. For instance, the top layer can be introduced with antibacterial particles, while another layer can be enhanced with fillers to increase wear resistance. The study reveals the varying antibacterial effects of spherical particles versus flat flakes and the different scratch hardnesses induced by changes in pH, number of layers, and particle introduction.

In this study, tungsten disulfide–zinc (WS₂-Zn) composite films were generated on polyether ether ketone (PEEK) disks by an atmospheric pressure plasma jet (APPJ) equipped with a shrouding attachment. The friction and wear properties of the WS₂-Zn coatings were intensively investigated by using a rotational ball-on-disk setup under dry sliding and ambient room conditions. In order to gain more information about the lubrication mechanism, the coating areas as deposited and the worn areas (i.e., in the wear track) were analyzed with a scanning electron microscope (SEM) with regard to their chemical composition in depth by energy-dispersive X-ray spectroscopy (EDS). X-ray photoelectron spectroscopy (XPS) was conducted to obtain precise chemical information from the surface. The results indicated that WS₂-Zn coatings significantly improved the tribological properties, exhibiting a coefficient of friction (COF) of <0.2. However, the tribological performance of the coatings is strongly dependent on the plasma process settings (i.e., plasma current, dwell time of the powder particles in the plasma jet), which were tuned to reduce the oxidation by-products of WS₂ to a minimum. The COF values achieved of the dry lubricant films were significantly reduced in contrast to the uncoated PEEK by a factor of four.