S Bärwulf

Tribological properties, phase generation and high temperature phase stability of tungsten- and vanadium-oxides deposited by reactive MSIP-PVD process for innovative lubrication applications

Abstract The tungsten and vanadium oxides are promising to be usable as solid lubricants at elevated temperatures because of their ability to form oxygen deficient Magneli-phases. As a matter of fact, metal-oxides are interesting for tribological insets at atmospheric conditions because of their expected oxidation stability and low adhesion. The study reports about the deposition of tungsten and vanadium oxides in a reactive d.c. mode by the MSIP- (Magnetron Sputtering Ion Plating) PVD process and especially about the influence of the oxygen content in the sputtering atmosphere as well as the deposition temperature on the phase generation. A simplified ‘sputtering phase diagram’ of the binary systems V–O and W–O as a function of the deposition temperature (378–650 K) and the oxygen content (0–50%) was determined. Furthermore, it was shown that the tested vanadium-oxides are phase stable up to 878 K and the tungsten-oxides up to 1100 K (measured in a high-temperature XRD facility). Additionally tribological properties of the deposited oxide coatings, like the friction coefficient vs. steel, will be presented. For polished and WOx coated samples a friction coefficient of μ≈0.2 against steel was measured at room temperature. The coatings were analyzed by various testing methods to characterize the tribological, mechanical and structural properties, like SEM, nanoindentation, (high-temperature)-XRD and pin-on-disk.

Mechanical properties of EB-PVD-thermal barrier coatings by nanoindentation

Abstract In the present work EB-PVD zirconia thermal barrier coatings were examined by nanoindentation. Because of the microstructure of EB-PVD-coatings, the mechanical properties in the vertical and the horizontal direction are completely different. Therefore the indents were performed on cross-sections and on the coatings’ surface itself. Because of the expected different behavior at the grain boundaries and the grains, the measurement locations were randomly chosen. The measured property was the Young’s modulus. For a better interpretation, the measurement results were described by the method of Weibull distribution. The measured values showed a significant dependency with the substrate temperature and a low dependency with oxygen partial pressure during the deposition process. Non-stoichiometric phases within the zirconia showed a complete different mechanical behavior.

Structure and properties of PVD-coatings by means of impact tester

Abstract Machine parts like rolling bearings or gears are stressed during operation in a changing mechanical strain. This causes wear by impacts and wear by rolling which is marked by the so-called surface ruin. The appearance of surface fatigue is based upon structural transformation, cracking and cracking-growth processes and ends with the separation of debris particles caused by the above-mentioned permanent changing strain [K.-H. Habig, Verschleis und Harte von Werkstoffen, Carl Hanser Verlag Munchen Wien, S. 203ff, 1980]. The final stage, which is equivalent to the component failure, is the so-called ‘pitting’ on the technical surface, which is characteristically named ‘surface fatigue’. The impact tester is used for detailed research on failure mechanisms of thin films. Statements about the adherence of hard material coatings under dynamic compressive stress can be made using this test method, due to the possibility of simulating some effects of rolling strain. Therefore, a hard metal ball strikes with a frequency of up to 50 Hz on to the surface. The altitude stress can be varied to obtain a detailed evaluation of fatigue strength under reversal strain. Selected hard material coatings were analyzed after testing with the described method applying an impact force of 300 N, 500 N and 700 N. In the framework of this presentation, MSIP (Magnetron Sputter Ion Plating) coatings on titanium- and chromium basis were used. The fatigue defects and the results of this study will be discussed relative to structure and morphology of thin films.

Properties of tungsten and vanadium oxides deposited by MSIP–PVD process for self-lubricating applications

Abstract The tungsten and vanadium oxides are known to be usable as solid lubricants at elevated temperatures. So far they have been used mainly as powdery materials for tribological applications or as a component of ceramics. Metal oxides are interesting for tribological insets at atmospheric conditions because of their oxidation stability. This study reports on investigations to find stable process windows for the deposition of tungsten and vanadium oxides in a reactive and non-reactive mode by the magnetron sputter ion plating–PVD-process. One focus of the study is the metal oxide phases generated in the MSIP-process under various conditions and their mechanical and metallographic properties. Coatings were deposited and analyzed by various testing methods to characterize the mechanical and structural properties, such as SEM, scratch-testing, Rockwell test, nanoindentation and XRD. Stable process windows will be presented for the reactive mode as well as the influence of different process parameters to phase generation, microstructure and the material properties. The influence of process-parameters on the deposition rate (d.c. versus r.f. mode, reactive versus non-reactive mode) is of great interest to evaluate the economic relevance. It will be shown that it is possible to deposit vanadium and tungsten oxides despite target contamination effects in wide ranges by adapting the reactive gas-flow, the total gas pressure and the target power.

Characteristic curves of voltage and current, phase generation and properties of tungsten- and vanadium-oxides deposited by reactive d.c.-MSIP-PVD-process for self-lubricating applications

Abstract Various transition metal oxides, like tungsten and vanadium oxides, are promising to be usable as solid lubricants at elevated temperatures because of their possible formation of Magneli-phases. So far, they have mainly been investigated as powdery material for tribological applications. Metal-oxides are interesting for tribological insets under atmospheric conditions because of their expected oxidation stability and low adhesion. This study reports investigations made to find stable process windows for the deposition of tungsten and vanadium oxides in a reactive d.c. mode by the MSIP-PVD-process. Therefore, the voltage–current characteristics were measured and a correlation between the phase generation of polycrystalline VO2 as well as polycrystalline V2O5 and the electric process parameters were identified. For tungsten oxides, no comparable correlation was found, even if there was a distinct formation of a metallic and a W3O-phase. As a result, a simplified ‘phase diagram’ of the binary systems VO and WO as a function of the deposition temperature (378–650 K) and the oxygen content (0–50%) will be presented. Furthermore, the deposited metal oxide-phases and selected mechanical properties, like the hardness and elastic-modulus (measured by nanoindentation) will be discussed. The coatings were analyzed by various testing methods to characterize their structural and mechanical properties, especially with XRD and nanoindentation.

Magnetron sputtered titanium nitride thin films on thermoplastic polymers

Abstract Enhancing the durability of thermoplastic polymers is desirable for improved wear resistance (rubbing, scratching, impact) of plastics in particle sensitive environments. In this investigation poly(butylene terephthalate) (PBT), poly(amide)6.6 (PA) and poly(carbonate) (PC) were chosen as substrate material. The selected coating material was titanium nitride (Ti–N), which is known as wear resistant coating in various applications like drilling and for other machining tools demanding highly durable surfaces. The Ti–N thin films were mainly deposited by magnetron sputter ion plating (MSIP) with different plasma pre-treatments to improve the adhesion. Therefore, it was necessary to vary different parameters of the plasma pre-treatment process, like the etching gas pressure, the r.f. etching power and the etching time, as well as parameters of the deposition process. Based on these investigations the influence of important MSIP process parameters on the deposition rate and mechanical properties was analyzed. It will be shown that in the reactive MSIP mode, deposition rates up to 5 μm/h are attainable (film thickness up to 3.5 μm) in a laboratory plant (Leybold Z 400). Coatings deposited on steel substrates and hard metals were used as references. The influence of selected process parameters (e.g. deposition rate) on the microstructure and the attainable film thickness, from which the deposition rate was deduced, were analyzed by scanning electron microscopy (SEM).

Magnetron-sputtered hard material coatings on thermoplastic polymers for clean room applications

Abstract Even under demanding environments, such as clean rooms, polymers are already used in different ranges of applications. The wear and particle generation within a specific particle size under mechanical stress is a limiting factor, as are high material and cleaning costs. Building on this state-of-the-art basis, our aim was to develop an innovative material concept that would allow the application of a thermoplastic polymer coated with a thin hard material (thickness up to 2.5 μm). Therefore, it was necessary to improve the wear resistance, the adherence between the polymer and the coating as well as to reduce the interaction with the aluminum (A6061) counterbody which functions as the tribological partner in the application. To align the aims and economics of the project, the production process consisted of only two phases: first, the injection moulding process that was then followed by a MSIP process including a plasma pretreatment. In this investigation, poly(butyleneterephthalate) (PBT), poly(amide) 6.6 (PA 6.6) and poly(carbonate) PC were chosen as substrate material. The coating materials presented here were based on titanium (Ti-N). The thin films were deposited by magnetron sputter ion plating (MSIP) because of its low defect rate and wide range of parameter variation possibilities to reduce the thermal stress during the coating process. The process parameters influence on the microstructure, extending from amorphous to columnar (crystalline) as well as the film thickness were analysed by SEM. Selected results of different plasma pretreatments to improve the adhesion for specific polymers will be discussed and presented. It will be shown that it is possible to improve the adherence between the film and the plastic substrate and to reduce the particle generation after the appropriate etching and coating process has taken place.