Jürgen M. Lackner

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.

Growth Structures and Phase Formation in Industrially Room-Temperature Pulsed Laser Deposited FCC Ti-Based Nitride Coatings

The current work focuses on the materials science aspects of the growth phenomena of titanium-based coatings TiN, (Ti,Al)N and (Ti,Al)(C,N) with face-centered cubic lattice structure, deposited by the industrially-styled Pulsed Laser Deposition (PLD) technique at room temperature. hese coating materials are widely spread in mechanical, tribological and decorative applications due to their exceptional physical and chemical properties. Recently, the trend of using temperaturesensitive materials like polymers and tool steels of the highest hardness demands new lowtemperature coating techniques for protective surface finishing as well as for functionalization of the surfaces. These titanium-based compounds can fulfill a wide range of these demands, but up to now there is a lack of industrially designed vacuum coating techniques operating at temperatures lower than 50 °C necessary for these materials. The PLD process is known as one of the most promising candidates for such coating demands. But up to now PLD is only a well-established laboratory coating technology and has not become a standard industrial coating technique despite its outstanding process features. The missing of PLD coating systems, which fulfill the requirements for industrial applications like high-rate deposition and adequate sizes of deposition chambers, is considered as one of the main obstacles for a breakthrough of the PLD technique. To overcome this problem an industrially designed PLD coating system has been developed and built at the Laser Center Leoben of JOANNEUM Research Forschungsgesellschaft mbH.

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.

Using of laser ablation to fabrication nanocrystalline multilayer coatings for biomedical and tribological application

Titanium nitride (TiN) is regarded as a potential biomaterial for blood-contact applications. TiN thin films were fabricated by pulsed laser deposition with the Nd:YAG laser on biologically applied polyurethane. Transmission electron microscopy (TEM) study of 350 nm thick films revealed columnar structure. Such films were observed to be brittle. In order to improve the coatings elasticity, the thickness was reduced to 50nm, which limited the deposition mechanism operation to the early stage. A biological test showed that TiN surface film produced on polyurethane is characterized by good biocompatibility and decreased surface affinity for cell adhesion. The physical explanation of TEM images was based on the performed finite element calculations of the temperature and stress distribution using the ADINA program. Boron nitride thin layers were produced by means of the pulsed laser deposition technique from hexagonal boron nitride target. Two types of laser i.e. Nd:YAG with Q-switch as well as KrF coupled with RF generator were used. Influence of deposition parameters on surface morphology, phase composition as well as mechanical properties is discussed. There are an increasing number of applications in tribology where the properties of a single material are not sufficient. One way to surmount this problem is to use a multilayer coating. Application of metallic interlayers improves adhesion of nitride hard layer in multilayer systems. Tribological coatings consisted of 4, 8 and 32 layers of Cr/CrN and Ti/TiN types were fabricated with the PLD technique. It is found in transmission electron examinations on thin foils prepared from cross-section that both nitride-based multilayer structures studied are characterized by small columnar crystallite sizes and high defect density, what might raise their hardness but compromise coating adhesion. The intermediate metallic layers contained larger sized and less defective columnar structure compared to the nitride layers, which should improve the coatings toughness. Switching from single layer to multi-layer metal/nitride composition improved resistance to delamination.

The cell niches reproducing surface structure

The future and the development of science is therefore seen in interdisciplinary areas such as biomedical engineering. Self-assembled structures, similar to stem cell niches would inhibit fast division process and subsequently capture the stem cells from the blood flow. By means of surface topography and the stiffness as well as microstructure progenitor cells should be differentiated towards the formation of endothelial cells monolayer which effectively will inhibit activation of the coagulation cascade. The idea of the material surface development met the interest of the clinical institutions, which support the development of science in this area and are waiting for scientific solutions that could contribute to the development of heart assist systems. This would improve the effciency of the treatment of patients with myocardial failure, supported with artificial heart assist systems. Innovative materials would enable the redesign, in the post project activity, construction of ventricular heart assist.

The Influence of the Mechanical Properties of a-C:H Based Thin Coatings on Blood-Material Interaction

An interaction of blood with artificial materials is an important aspect in designing cardiovascular tissue analogues. The processes occurs on liquid/solid interface depends both on structural and mechanical properties of biomaterials. Main goal of the work was to develop novel blood contacting materials in the form of thin coatings with anti-thrombogenic properties by reduction of shear stress improving sufficient washing of biofunctional-adapted surfaces. Preliminary studies and simulations led us to carbon based thin coatings considered as silicon doped amorphous carbon. The rigidity of the surface design of materials dedicated for the biomedical purpose is of particular importance. The paper presents an analysis of the impact of material stiffness and mechanical for interaction with blood cells. Material analysis of in the context of the mechanical properties showed changes in stiffness depending on the thickness of the coating. The Young modulus and hardness of materials were examined by indentation test using Berkovich indenter geometry. Cell-material interactions were assessed using the cellular components of blood. Shear stress on the between the cell-and material were considered taking into account red blood cells and platelets concentrates.

TEM Investigations of Wear Mechanisms of Single and Multilayer Coatings

The titanium nitride (TiN) is of special interest due to its corrosion resistance and high hardness (R. F. Bunshah, 2001, D. S. Rickerby & A. Matthews, 1991). The other promising material for wear resistant applications is amorphous, hydrogenated carbon (a-C:H). The aC:H coatings are characterised by very low friction and biological inertness (V. Kumar et al., 2011). The tribologyrelated engineering applications for highlystressed components require the development of new multifunctional thin films materials providing superior mechanical, tribological, chemical and hightemperature performance. It could be achieved by connecting the properties of different type of materials in multilayer coatings (Li Chen et al., 2008, M. Stueber et al., 2009, E. Martinez et al., 2003, J. Smolik et al., 1999, Y. L. Su et al., 1998, N. Duck et al., 2001, M. Nordin et al., 1999).