Wolfgang Waldhauser

Pulsed laser deposition of diamond-like carbon coatings for industrial tribological applications

Abstract The aim of the present work is the investigation of the structural, mechanical and tribological properties of low-wear diamond-like carbon (DLC) coatings for industrial applications. Amorphous hydrogen-free (a-C) and hydrogenated (a-C:H) DLC coatings were coated onto various steel substrates (AISI 1045H, B7, H13, D2, M2) with hardness levels varying from 28 to 66 HRC, by employing the pulsed laser deposition (PLD) method. Therefore, graphite targets were ablated with the 1064 nm wavelength of an Nd:YAG laser in argon and C 2 H 2 atmospheres. The high mean laser power of the applied PLD equipment guarantees deposition rates competitive to other physical vapour deposition (PVD) techniques. Because of the specific process conditions and the use of pure titanium adhesive interface layers, coatings with high adhesion to the substrates were produced at room temperature. The investigations of the coatings by means of light and scanning electron microscopy reveals the high surface quality and extremely dense coating structures. XRD measurements indicated the amorphous structure of the coatings. The nature of the chemical bonding was examined by XPS, indicating different amounts of sp 3 carbon bonds. Pin-on-disc tests against 100Cr6 ball-bearing steel balls as counterparts show an excellent wear resistance of a-C and a-C:H DLC coatings on all different steel substrates. These results, demonstrated the applicability of PLD–DLC coatings for wear protection of high precision components in the field of tools and mechanical components.

Room temperature deposition of (Ti,Al)N and (Ti,Al)(C,N) coatings by pulsed laser deposition for tribological applications

Abstract Titanium–aluminium based nitride (Ti,Al)N and carbonitride (Ti,Al)(C,N) hard coating systems possess excellent tribological behaviour in metal cutting and polymer forming contacts. In the present work (Ti,Al)N and (Ti,Al)(C,N) coatings were deposited by employing the pulsed laser deposition (PLD) technique. A pulsed Nd:YAG laser with 1064 nm wavelength was used for the vaporization of TiAl targets in low-pressure N2 or N2/C2H2, atmospheres at room temperature. The highly ionized metal vapour was deposited onto polished substrates (molybdenum, AISI D2). The coatings were characterized by light-microscopy, scanning electron microscopy, X-ray diffraction and hardness tests. The variation of the deposition parameters causes a change of the chemical composition, the texture and crystallinity of the coatings and, consequently, the mechanical properties and tribological behaviour. The latter was characterized in pin-on-disc tests at room temperature by using coated discs and uncoated AISI 52100 (DIN 100Cr6) steel and alumina pins as counterparts. The results demonstrate the excellent industrial applicability of these coatings for cold-forming operations: very low-wear rates were found for the (Ti,Al)N coatings. In contrast, the (Ti,Al)(C,N) coatings possess low-friction coefficients of approximately 0.2. As an outstanding advantage of these coatings, which were deposited at the room temperature by the PLD process, their excellent adhesion to the substrate can be pointed out, reaching the highest level (HF 1) in the Rockwell indentation test.

Pulsed laser deposition: a new technique for deposition of amorphous SiOx thin films

Abstract Pulsed laser deposition (PLD) is a physical vapour deposition coating technique for the production of thin films with complex chemical compositions. One of the main advantages of PLD is that excellent coating properties can be achieved even at low deposition temperatures. However, particulate defects in the growing films resulting from the evaporation process are often mentioned as the most important disadvantages of the PLD process. Unfavourable optical, thermo-physical and mechanical properties of the target material evaporated by laser radiation promote the formation of particulate defects. This paper presents some results on silicon-based PLD-films with reduced density of particulates. Silicon, SiO x and SiO 2 thin films were deposited by laser ablation from silicon targets with a high power pulsed Nd:YAG laser of 1064 nm wavelength in argon and oxygen containing atmospheres. The substrates were arranged in shaded off-axis geometry. The chemical composition and structure of the films were investigated employing transmission electron microscopy (TEM), secondary ion mass spectroscopy, X-ray photoelectron spectroscopy and ellipsometry. The results demonstrate the capability of PLD for the deposition of SiO x films with varying composition (0⩽ x ⩽2) by shaded off-axis PLD. The results of TEM and spectroscopic ellipsometry are indicating amorphous film structures in all cases.

Inorganic PVD and CVD Coatings in Medicine — A Review of Protein and Cell Adhesion on Coated Surfaces

The functionalization of biomaterials for implants becomes increasingly important for designing bioinert and bioactive surfaces to reduce the impact of implantation to human body (inflammation, encapsulation) and extend the lifetime of implants. Even pharmacological effects can be triggered by nanomaterials like thin films and nanoparticles in medical treatment. However, the systematic knowledge of the interactions between cells and artificial, inorganic materials is poor yet. Finding the decisive influences for high hemocompatibility or osseointegration is very difficult. Surface chemistry including wetting behaviour, surface charge, homogeneity and functional groups as well as surface topography are some of the fundamental surface parameters defining the cell–surface interaction. Focusing on physical and chemical vapour deposited thin films and coatings, this review will provide for a better understanding of biocompatible coating materials like titanium- and carbon-based compounds and calcium phosphates.

Tribology of bio-inspired nanowrinkled films on ultrasoft substrates

Biomimetic design of new materials uses nature as antetype, learning from billions of years of evolution. This work emphasizes the mechanical and tribological properties of skin, combining both hardness and wear resistance of its surface (the stratum corneum) with high elasticity of the bulk (epidermis, dermis, hypodermis). The key for combination of such opposite properties is wrinkling, being consequence of intrinsic stresses in the bulk (soft tissue): Tribological contact to counterparts below the stress threshold for tissue trauma occurs on the thick hard stratum corneum layer pads, while tensile loads smooth out wrinkles in between these pads. Similar mechanism offers high tribological resistance to hard films on soft, flexible polymers, which is shown for diamond-like carbon (DLC) and titanium nitride thin films on ultrasoft polyurethane and harder polycarbonate substrates. The choice of these two compared substrate materials will show that ultra-soft substrate materials are decisive for the distinct tribological material. Hierarchical wrinkled structures of films on these substrates are due to high intrinsic compressive stress, which evolves during high energetic film growth. Incremental relaxation of these stresses occurs by compound deformation of film and elastic substrate surface, appearing in hierarchical nano-wrinkles. Nano-wrinkled topographies enable high elastic deformability of thin hard films, while overstressing results in zigzag film fracture along larger hierarchical wrinkle structures. Tribologically, these fracture mechanisms are highly important for ploughing and sliding of sharp and flat counterparts on hard-coated ultra-soft substrates like polyurethane. Concentration of polyurethane deformation under the applied normal loads occurs below these zigzag cracks. Unloading closes these cracks again. Even cyclic testing do not lead to film delamination and retain low friction behavior, if the adhesion to the substrate is high and the initial friction coefficient of the film against the sliding counterpart low, e.g. found for DLC.

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.

Hemocompatibility of Inorganic Physical Vapor Deposition (PVD) Coatings on Thermoplastic Polyurethane Polymers

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.

Plasma Polymerization Inside Tubes in Hexamethyldisiloxanes and Ethyne Glow Discharges: Effects of Deposition Atmosphere on Wetting and Ageing in Solvents

The coating deposition inside tubes becomes increasingly important for fluidic applications, in which inner surfaces are chemically and mechanically strained by the flowing liquid and by scratching of particles. The developed process for tube coating, presented in this work, is based on the discharge in the precursor gas atmosphere between two mesh electrodes at the ends of the tube. The gas mixture is introduced on one end and pumped through the electrode on the other end. Igniting plasma inside the tube, the tube walls are the barrier to the atmosphere. Especially pulsed DC discharges for plasma polymerization in this alignment lead to good coating results, which is shown in this work focusing on deposition in pure and mixed hexamethyldisiloxane, ethyne, and oxygen atmospheres. Chemical binding, wetting, and ageing are strongly influenced by the choice of the gas mixtures. Sufficient oxygen partial pressure in the deposition atmosphere leads to hydrophilic behavior of the SiO2-like polymer-like carbon coatings, all other applied atmospheres to generally hydrophobic behavior of pure and Si-doped plasma polymers, respectively.

Growth, structure and stability of sputter-deposited MoS2 thin films

Molybdenum disulphide (MoS2) thin films have received increasing interest as device-active layers in low-dimensional electronics and also as novel catalysts in electrochemical processes such as the hydrogen evolution reaction (HER) in electrochemical water splitting. For both types of applications, industrially scalable fabrication methods with good control over the MoS2 film properties are crucial. Here, we investigate scalable physical vapour deposition (PVD) of MoS2 films by magnetron sputtering. MoS2 films with thicknesses from ≈10 to ≈1000 nm were deposited on SiO2/Si and reticulated vitreous carbon (RVC) substrates. Samples deposited at room temperature (RT) and at 400 °C were compared. The deposited MoS2 was characterized by macro- and microscopic X-ray, electron beam and light scattering, scanning and spectroscopic methods as well as electrical device characterization. We find that room-temperature-deposited MoS2 films are amorphous, of smooth surface morphology and easily degraded upon moderate laser-induced annealing in ambient conditions. In contrast, films deposited at 400 °C are nano-crystalline, show a nano-grained surface morphology and are comparatively stable against laser-induced degradation. Interestingly, results from electrical transport measurements indicate an unexpected metallic-like conduction character of the studied PVD MoS2 films, independent of deposition temperature. Possible reasons for these unusual electrical properties of our PVD MoS2 thin films are discussed. A potential application for such conductive nanostructured MoS2 films could be as catalytically active electrodes in (photo-)electrocatalysis and initial electrochemical measurements suggest directions for future work on our PVD MoS2 films.

Embedded simulation for automation of material manipulators in a PVD coating process

For the automation of a production system a hardware-in-the-loop (HIL) simulation model of the mechanical system was developed and embedded on the controller. In a second level, the controller was simulated on a PC for designing and testing the human-machine interface (HMI). The task of the system is a PVD (physical vapor deposition) coating process for materials, which involves pulsed laser deposition and magnetron sputtering. It requires positioning devices to move material probes as well as to manipulate laser target materials in a vacuum chamber. As a result of using simulation, the start-up phase was shortened and production was resumed faster. The need of software changes after deployment was reduced. With the increasing capabilities of modern simulation software and controller hardware it turns out, that virtual start-up, factory acceptance test and functional validation are practicable also for small projects.