Michael Griepentrog

Ti/TiN multilayer coatings : deposition technique, characterization and mechanical properties

Abstract Ti/TiN multilayer coatings with multilayer periods in the range 5–50 nm and a final thickness of 2 μm were deposited on steel substrates by cyclic modulation of nitrogen gas flow into the chamber of a PVD sputtering device. Coating characterization was performed by cross-sectional transmission electron microscopy, glancing-angle X-ray diffraction and instrumental indentation testing. Individual α-titanium and titanium nitride layers were always observed, although for the finer microstructures, the TiN layers were thicker than the Ti layers by a factor three. The plastic hardness of the films increased steadily with decreasing layer spacing, following a Hall–Petch relationship. Finally, a hardness value of 42 GPa was reached, which is similar to that of a thick TiN monolayer, prepared under the same coating conditions.

Hard coatings on magnesium alloys by sputter deposition using a pulsed d.c. bias voltage

Abstract An increasing use of magnesium-based light-metal alloys for various industrial applications was predicted in different technological studies. Companies in different branches have developed machine parts made of magnesium alloys (e.g. cars, car engines, sewing and knitting machines). Hence, this work was started to evaluate the ability of hard coatings obtained by physical vapour deposition (PVD) in combination with coatings obtained by electrochemical deposition to protect magnesium alloys against wear and corrosion. TiN hard coatings were deposited onto magnesium alloys by unbalanced magnetron sputter deposition. A bipolar pulsed d.c. bias voltage was used to limit substrate temperatures to 180 °C during deposition without considerable loss of microhardness and adhesion. Adhesion, hardness and load-carrying capacity of TiN coatings deposited directly onto magnesium alloys are compared with the corresponding values of TiN coatings deposited onto substrates which had been coated electroless with an Ni-P alloy interlayer prior to the PVD.

The Determination of the Efficiency of Energy Dispersive X-Ray Spectrometers by a New Reference Material

A calibration procedure for the detection efficiency of energy dispersive X-ray spectrometers (EDS) used in combination with scanning electron microscopy (SEM) for standardless electron probe microanalysis (EPMA) is presented. The procedure is based on the comparison of X-ray spectra from a reference material (RM) measured with the EDS to be calibrated and a reference EDS. The RM is certified by the line intensities in the X-ray spectrum recorded with a reference EDS and by its composition. The calibration of the reference EDS is performed using synchrotron radiation at the radiometry laboratory of the Physikalisch-Technische Bundesanstalt. Measurement of RM spectra and comparison of the specified line intensities enables a rapid efficiency calibration on most SEMs. The article reports on studies to prepare such a RM and on EDS calibration and proposes a methodology that could be implemented in current spectrometer software to enable the calibration with a minimum of operator assistance.

Biological response to micron- and nanometer-sized particles known as potential wear products from artificial hip joints: Part II: Reaction of murine macrophages to corundum particles of different size distributions.

Macrophages play a pivotal role in tissue reaction and immune response. They recognize, phagocytose particles and generate cytokines to influence local cellular reactions. Friction and wear of implant components usually generates microparticles (MP) in a size range of 1-10 mum and nanoparticles (NP) in the range of 10-1000 nm. To investigate the possible impact of MP or NP on cellular reactions, we exposed murine macrophages (RAW264.7) to corundum MP and NP. The same mass was used in both NP and MP cell culture solutions, i.e. there were more NP than MP per identical volumes of culture solution. After 4, 24, 48, 72, and 96 h aliquots of cell culture supernatants were tested for different cytokines, growth factors and nitric oxide. Macrophages were stained with MGG (May-Grünwald Giemsa), counted and morphologically characterized by scanning electron microscopy and transmission electron microscopy. Particles were attached to cell surfaces and phagocytosed within cells. Cells stimulated with particles or lipopolysaccharides for positive controls showed surface modifications indicating enhanced function. Although only marginal differences between negative controls and particle-stimulated cells were observed in respect to cytokine production, exposure to corundum particles led to a decrease in the number of vital macrophages and to an increase in the number of giant cells. Corundum NP formed micron-sized aggregates in the cell culture medium and led to the production of more giant cells than MP. Sodiumdodecylsulfate polyacrylamide gel electrophoresis of the cell culture medium with particles proved the adsorption of proteins to particles.

Properties of TiN hard coatings prepared by unbalanced magnetron sputtering and cathodic arc deposition using a uni- and bipolar pulsed bias voltage

Abstract TiN hard coatings have been prepared by unbalanced magnetron (UBM) sputtering and cathodic arc deposition using uni- and bipolar pulsed bias voltages. For UBM sputtering using a unipolar pulsed bias voltage the average substrate bulk temperature Ts was reduced to 220 °C without considerable loss of microhardness and adhesion by variation of the pulse parameters. Determination of the average energy Ep delivered to the growing film per deposited particle leads to values lower than the critical transition energy (150 eV atom−1) between open porous and dense coatings. Using a bipolar pulsed bias voltage Ts decreased with increasing duration ton+ of the positive bias pulse. It was found that Ep increased with increasing ton+ up to values found for d.c. bias voltage. The coatings prepared using a bipolar pulsed bias voltage at low Ts are dense and in compressive stress with acceptable microhardness and adhesion. First results of the investigation of TiN coatings prepared by cathodic arc deposition using unipolar pulsed bias are given.

Round Robin exercise: Coated materials for glow discharge spectroscopy

A Round Robin (RR) exercise on selected coated materials has been carried out with the aim of finding the optimal conditions for the analysis of nitride layers with GD-OES. Such pre-normative work is necessary for the evaluation of parallel development of the production of nitride layers as certified reference materials (CRMs). Two types of samples, Ti–N layer and V–N layer, respectively, with chemical compositions close to stoichiometry and a thickness of ∼3 μm, deposited on a steel substrate, have been provided to the RR participants. Additionally, another type of sample, a (100 nm CrNi/100 nm Cu) multilayer (ML) stack deposited on silicon wafer has also been included in the RR. This sample can be used as a CRM for checking GD spectrometer conditions and it has been proved helpful in further development of GDS instrumentation and methodology. The RR exercise has been performed in the frame of the EC Thematic Network on Glow Discharge Spectroscopy for Spectrochemical Analysis (‘GDS-Net’).

Some properties of the mixed GaS0.4Se0.6 nonlinear crystal in comparison to GaSe

Two essential advantages can be expected from adding S to the well known nonlinear crystal GaSe: increase of the bandgap value or the short wave cut-off limit and improved hardness. Recently, we confirmed that the non-centrosymmetric structure of GaSe is preserved up to a GaS content of 40 mol. % while the nonlinear coefficient d22 is reduced by only 24%. The increased band-gap results also in higher surface damage threshold. Our preliminary Sellmeier equations for GaS0.4e0.6 were based on refractive index measurements. These equations are refined in the present work by fitting second-harmonic generation and optical parametric amplification phase-matching angle data in the mid-infrared as well as birefringence data in the visible and near-infrared obtained with thin phase retardation plates. The two-photon absorption effect was studied for GaS0.4e0.6 and GaSe using amplified picosecond pulses at 1064 nm, at a repetition rate of 10 Hz. For intensities in the GW/cm2 range, the two-photon absorption coefficient of GaS0.4e0.6 for the o-polarization is 3.5 times smaller than the corresponding coefficient of GaSe. This means that GaS0.4e0.6 could be safely used in Nd:YAG laser pumped nanosecond optical parametric oscillators or picosecond optical parametric amplifiers, without nonlinear absorption losses. The dynamic indentation measurements with Berkovich type indenter of c-cut GaS0.4e0.6and GaSe plates indicate about 30% higher indentation modulus and microhardness of GaS0.4e0.6 in comparison to GaSe.

Biological response to micron- and nanometer-sized particles known as potential wear products from artificial hip joints: Part I: Selection and characterization of model particles

The aim of this work was to select and characterize model particles, which correspond to real wear products from artificial hip joints, and to investigate the dispersing behavior of these powders. Commercially available nano and microparticles of corundum, graphite, and chromium oxide were selected or alternatively self-produced by milling. These powders were characterized regarding density, specific surface area, crystalline phases, particle size distributions and shape. Volume-based particle size distributions Q(3)(d) were measured after dispersing in water, water with dispersant, Ringers solution, and cell culture solution (Dulbeccos Modified Eagles Medium (DMEM)) by laser diffraction and ultrasonic spectroscopy. Nanopowders formed agglomerates in the micrometer range in cell culture solutions. The micropowders showed only a marginal agglomeration. The median diameters of the dispersed nanopowders were even bigger than those of micropowders. Calculations of the number-based size distribution Q(0)(d) showed that in spite of the agglomeration the predominant number of the nano and microparticles is in the sub micrometer range, with only one exception, the micrographite powder.

INO–A WWW information system for innovative coatings and surface technology

Abstract In the last years, a lot of research work has been performed in the field of surface coatings and thin films technology, often supported by governmental research programs, as i.e. in Germany, the ‘Thin Film Technology’ and ‘OSTec’ research programs. But up until now, there is still a lack in transfer of this large amount of knowledge created by research activities on to industrial application and commercialization. To overcome this problem, a new web based information system has been developed (http://www.schichttechnik.net), which in a first step will make the whole content of the German OSTec research program (approx. 180 research reports) of the last 10 years available. In further steps, data from products of coating suppliers and other research programs will be taken into account. The database contains the following sections: definition of the coating system, deposition equipment, deposition processes, application properties, test procedures and test equipment, information about standardization and base information about coating processes etc. It will be possible to search for coatings by material properties and functions of coatings, considering also restriction on the substrate. In addition, searching regarding combination of properties, e.g. for wear-resistant, conductive, decorative coatings etc. will also be possible.

Femtosecond Laser Texturing of Surfaces for Tribological Applications

Laser texturing is an emerging technology for generating surface functionalities on basis of optical, mechanical, or chemical properties. Taking benefit of laser sources with ultrashort (fs) pulse durations features outstanding precision of machining and negligible rims or burrs surrounding the laser-irradiation zone. Consequently, additional mechanical or chemical post-processing steps are usually not required for fs-laser surface texturing (fs-LST). This work aimed to provide a bridge between research in the field of tribology and laser materials processing. The paper reviews the current state-of-the-art in fs-LST, with a focus on the tribological performance (friction and wear) of specific self-organized surface structures (so-called ripples, grooves, and spikes) on steel and titanium alloys. On the titanium alloy, specific sickle-shaped hybrid micro-nanostructures were also observed and tribologically tested. Care is taken to identify accompanying effects affecting the materials hardness, superficial oxidation, nano- and microscale topographies, and the role of additives contained in lubricants, such as commercial engine oil.