B. Major

Primary and secondary carbides in high-speed steels after conventional heat treatment and laser modification

Complex structure examinations were performed on high-speed steels of different grades obtained using conventional metallurgy and produced by application of powder metallurgy. Hot hardness measurements were focused on the secondary carbide precipitation. Transmission electron microscopy and X-ray diffraction studies established the type of primary carbides and the amount of retained austenite. Scanning electron microscopy examinations were used to calculate the volume fraction of primary carbides. The contribution of the applied heat treatment and laser modification by diode laser remelting to the residual stress state was studied. Energy filtering was used to study the secondary carbides of nanometer size.

Morphology of titanium nitride produced using glow discharge nitriding, laser remelting and pulsed laser deposition

Surface layers, produced on titanium alloys by means of glow discharge nitriding, laser modification by remelting using Nd:YAG or diode lasers in nitrogen environment and pulsed laser deposition by titanium target ablation in nitrogen environment, have been studied. Residual stresses were measured using an X-ray method and their values were related to the type of the applied technological process.

Bio-tribological TiN/Ti/a-C : H multilayer coatings development with a built-in mechanism of controlled wear

Development of a new generation of multilayer coatings as well as a microstructure understanding of the mechanisms operating at the smallest length scale (nano- and atomic-scale) during wear, opens an avenue for the fabrication of future high-tech functional surfaces. Coatings for the presented work were fabricated by a pulsed laser deposition supported by magnetron sputtering. Microstructure characterization has been performed on as-deposited coatings as well as on coatings after mechanical wear test. Thin foils for detailed TEM microstructure observation were cut directly from the mechanically deformed area, using the FIB technique. Wear mechanisms operating at the small length scale of TiN/Ti/a-C : H multilayer coatings subjected to mechanical wear was studied by means of transmission electron microscopy (TEM). Cracking of the multilayer systems propagated layer by layer. The highest stress concentration during mechanical uploading was moved through the multilayer coating by breaking only one layer at the time.

Hemocompatible, pulsed laser deposited coatings on polymers / Anwendung der Pulslaserbeschichtung zur Abscheidung von hämokompatiblen Beschichtungen auf Polymeroberflächen

Abstract State-of-the-art non-thrombogenic blood contacting surfaces are based on heparin and struggle with the problem of bleeding. However, appropriate blood flow characteristics are essential for clinical application. Thus, there is increasing demand to develop new coating materials for improved human body acceptance. Materials deposited by vacuum coating techniques would be an excellent alternative if the coating temperatures can be kept low because of the applied substrate materials of low temperature resistance (polymers). Most of the recently used plasma-based deposition techniques cannot fulfill this demand. However, adequate film structure and high adhesion can be reached by the pulsed laser deposition at room temperature, which was developed to an industrial-scaled process at Laser Center Leoben. Here, this process is described in detail and the resulting structural film properties are shown for titanium, titanium nitride, titanium carbonitride, and diamond-like carbon on polyurethane, titanium and silicon substrates. Additionally, we present the biological response of blood cells and the kinetic mechanism of eukaryote cell attachment. In conclusion, high biological acceptance and distinct differences for the critical delamination shear stress were found for the coatings, indicating higher adhesion at higher carbon contents. Zusammenfassung Derzeit verwendete Oberflächen für den Blutkontakt basieren im Allgemeinen auf Heparin, wobei es in der klinischen Verwendung leicht zum Problem von Blutungen kommen kann. Nichtsdestotrotz ist aber ein optimaler Blutfluss entscheidend, wodurch sich zunehmend die Forderung nach der Entwicklung von neuen Materialien mit verbesserter Körperakzeptanz stellt. Mittels Plasmaverfahren auf Oberflächen abgeschiedene Werkstoffe könnten zukünftig eine Alternative zu Heparin bieten, wenn die Temperaturen während des Herstellprozesses auf nahezu Raumtemperatur abgesenkt werden könnten, um vor allem die vielfach verwendeten Kunststoffe mit geringer Temperaturbeständigkeit beschichten zu können. Als eine der wenigen Techniken bietet sich dafür die Pulslaserabscheidung (PLD) an, welche zu einem industriell einsetzbaren Prozess am Laserzentrum Leoben entwickelt wurde. Diese Arbeit beschreibt die Hauptmerkmale dieses Prozesses und die sich ergebenden strukturellen Filmeigenschaften von Ti, TiN, Ti(C,N) und diamantähnlichem Kohlenstoff (DLC) auf Polyurethan-, Titan- und Siliziumoberflächen. Zudem werden die biologische Antwort von Blutzellen und die kinetischen Haftungsmechanismen von Eukaryotzellen dargestellt. Zusammengefasst zeigen diese Schichtwerkstoffe hohe biologische Akzeptanz und deutliche Unterschiede in den kritischen Scherspannungen zur Delamination, wobei eine höhere Zelladhäsion bei höheren Kohlenstoffgehalten erreicht wird.

Development and complex characterization of bio-tribological Cr/CrN + a-C:H (doped Cr) nano-multilayer protective coatings for carbon–fiber-composite materials

Carbon fiber structures provide strength, stiffness, and fatigue resistance. Carbon-based materials show, however, significant oxidative degradation in air beginning at temperatures in the region of 400 °C. Therefore, a coating concept for carbon–carbon composites consists of an inner part, which serves as a structural link with stress compensation ability to the carbon substrate, and an outer part, which acts as a diffusion barrier. In the presented paper, chromium/chromium nitride (Cr/CrN) multilayer structure has been selected as the inner part. The outer part of the coating, in the presented paper, was hydrogenated amorphous carbon (a-C:H). Among doping metals, Cr, as one of the carbide formed elements, possesses an attractive combination of properties (corrosion resistance, wear resistance, etc.). Thus, in the presented paper, a-C:H part of the coating was implanted by Cr nanocrystals. Coatings were deposited by means of magnetron sputtering technique. They were subjected to complex investigations. Mechanisms of a mechanical wear of analyzed systems were presented, focusing on the cracking propagation in ball-on-disc tests using a 1 N and 5 N applied loads for 20 000 cycles. Complex microstructure analysis of presented nano-multilayer coatings, before and after mechanical tests, were performed by means of transmission electron microscopy (TEM). The microstructure characterization revealed that cracking, which was propagating in the outer part of the coating (in the carbon part) in the layer with lower nano-particle content, was stopped at the interface with the higher nano-particle content layer. In the case of the inner part of the coating (Cr/Cr2N), ceramic layers showed brittle cracking, while metallic (Cr) ones deformed plastically.

Surface treatment of thin-film materials to allow dialogue between endothelial and smooth muscle cells and the effective inhibition of platelet activation

This work aims to reproduce the structure of a blood vessel. The surface modifications that were carried out concerned the creation of an appropriate environment for communication between tissues. Cell–material interactions were studied in this work. Samples for examination were prepared on polished silicon substrates and the sample surface was covered with different biocompatible coatings such as: diamond like carbon (a-C:H), titanium (Ti), titanium nitride (Ti:N), titanium carbonitride (a-C:H:Ti:N), titanium oxide (Ti:O), silicon doped diamond like carbon (a-C:H:Si) and titanium doped diamond like carbon (a-C:H:Ti). Physical vapour deposition (hybrid pulsed laser deposition) was chosen for coating fabrication and the coating thickness ranged from 200 nm to 1 μm. Based on a dynamic analysis using blood, which considered aggregate formation, platelet consumption and blood platelet activation, the most haemocompatible coating was chosen. The study also considered channels for the migration of cells. Using the laser ablation method, migration channels were fabricated. The width of each individual channel depended on the cell size, which was close to 10–30 μm. Cells were deposited directly on the migration channels. An influence of the heat affected zone on cell proliferation was observed. Porous coatings were deposited as the next step after channel formation. The coatings were stabilized by a cross linking chemical reaction using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide. Smooth muscle cells were deposited on the surface of samples without the porous coating, directly onto the migration channels. Human umbilical endothelial cells were deposited on the top of the synthetic porous coating. A de novo surface design for cardiovascular purposes with the function of providing oriented cell growth as well as allowing a dynamic dialogue between tissues was proposed.

Inner surface modification of the tube-like elements for medical applications

The objective of this work was to modify the inner surfaces of polymer tubes to improve their biocompatibility with blood cells. New materials that were designed to be placed in contact with blood during forced blood circulation were studied. The inner surfaces of these tubes were covered with anti-thrombogenic coatings. Materials based on silicon carbide, silicon oxide, and silicon nitride were deposited. Depending on the topography and the chemical nature of the inner vessel surface, a non-thrombogenic bio-surface, also called a neointima, was formed. Several expected applications of this work are discussed, including archetypal human blood vessels, the design of a nanostructural artificial substitute, optimising the surface using vacuum-coating techniques, characterising materials on multiple scales, and studying the blood-material interaction under dynamic conditions in an arterial flow environment. Several promising solutions for inhibiting the activation of the blood-clotting cascade via the use of appropriate surface architectures have been obtained. These solutions may be applied in advanced biocompatible cardiovascular implants.

Microstructure characterization of advanced protective Cr/CrN+a‐C:H/a‐C:H:Cr multilayer coatings on carbon fibre composite (CFC)

Studies of advanced protective chromium‐based coatings on the carbon fibre composite (CFC) were performed. Multidisciplinary examinations were carried out comprising: microstructure transmission electron microscopy (TEM, HREM) studies, micromechanical analysis and wear resistance. Coatings were prepared using a magnetron sputtering technique with application of high‐purity chromium and carbon (graphite) targets deposited on the CFC substrate. Selection of the CFC for surface modification in respect to irregularities on the surface making the CFC surface more smooth was performed. Deposited coatings consisted of two parts. The inner part was responsible for the residual stress compensation and cracking initiation as well as resistance at elevated temperatures occurring namely during surgical tools sterilization process. The outer part was responsible for wear resistance properties and biocompatibility. Experimental studies revealed that irregularities on the substrate surface had a negative influence on the crystallites growth direction. Chromium implanted into the a‐C:H structure reacted with carbon forming the cubic nanocrystal chromium carbides of the Cr23C6 type. The cracking was initiated at the coating/substrate interface and the energy of brittle cracking was reduced because of the plastic deformation at each Cr interlayer interface. The wear mechanism and cracking process was described in micro‐ and nanoscale by means of transmission electron microscope studies. Examined materials of coated CFC type would find applications in advanced surgical tools.

In vitro hemocompatibility on thin ceramic and hydrogel films deposited on polymer substrate performed in arterial flow conditions.

Hydrogel coatings were stabilized by titanium carbonitride a-C:H:Ti:N buffer layers deposited directly onto the polyurethane (PU) substrate beneath a final hydrogel coating. Coatings of a-C:H:Ti:N were deposited using a hybrid method of pulsed laser deposition (PLD) and magnetron sputtering (MS) under high vacuum conditions. The influence of the buffer a-C:H:Ti:N layer on the hydrogel coating was analysed by means of a multi-scale microstructure study. Mechanical tests were performed at an indentation load of 5 mN using Berkovich indenter geometry. Haemocompatible analyses were performed in vitro using a blood flow simulator. The blood-material interaction was analysed under dynamic conditions. The coating fabrication procedure improved the coating stability due to the deposition of the amorphous titanium carbonitride buffer layer.

Transition of Flake into Fibre Structure in Eutectic Al-Si

The work presents microstructures of the Al-Si eutectic alloy obtained within the range of solidification rates at various temperature gradients at which the transition of flake into fibre structure could be expected. The solidification conditions applied were growth rates ν = 300÷800 μm/s and temperature gradients G = 40÷250 K/cm. An influence of temperature gradient onto structure parameters λ and R has not been observed. An influence of temperature gradient onto the range of the transition flake into fibre has not been noted neither.