Fraunhofer Institute for Material and Beam Technology

Dresden, Germany

Fraunhofer Institute for Material and Beam Technology

Dresden, Germany
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Mabuchi Y.,Nissan Motor Co. | Higuchi T.,Nissan Motor Co. | Weihnacht V.,Fraunhofer Institute for Material and Beam Technology
Tribology International | Year: 2013

Hydrogen-free diamond-like carbon (DLC) coatings display markedly lower friction coefficients under a lubricated condition owing to the adsorption of oiliness agents and their decomposed components. This study examined the effect on friction properties of the sp2/sp3 bonding ratio of DLC coatings and the addition of nitrogen for improving surface wettability. Evaluations of friction properties under a lubricated condition showed that DLC coatings with a lower ratio of sp3 bonds and nitrogenated DLC coatings displayed higher friction coefficients. Results obtained by electron spin resonance revealed that adding nitrogen decreased the number of dangling bonds of DLC coatings in proportion to the sp3 bond ratio. Assuming that such dangling bonds are oiliness agent adsorption sites, it is concluded that adding nitrogen is not conducive to reducing friction coefficients. © 2013 Elsevier Ltd.

Scintilla L.D.,Polytechnic of Bari | Tricarico L.,Polytechnic of Bari | Wetzig A.,Fraunhofer Institute for Material and Beam Technology | Beyer E.,Fraunhofer Institute for Material and Beam Technology | Beyer E.,TU Dresden
International Journal of Machine Tools and Manufacture | Year: 2013

In this work the calculation of the process temperatures in fusion cutting was carried out based on the power balance approach. Cutting experiments with CO2 and disk lasers were performed on 1, 5 and 8 mm thick cold work tool steel sheets. The experimental, numerical and analytical evaluation of the single terms of the power balance equation allowed the explanation of the observed cut quality differences between disk and CO2 laser cuts. Lower process temperatures calculated by a power balance equation for disk laser cuts lead to the increase of viscosity of molten material. The subsequent increase in difficulty for ejection of the molten material from the cut kerf explains the worse cut quality if compared with CO2 laser cuts. Experimental evidence and theoretical calculations showed that the additional physical mechanisms like plasma formation should be considered in the overall power balance under particular cutting conditions. © 2013 Elsevier Ltd.

Strubel P.,Fraunhofer Institute for Material and Beam Technology | Thieme S.,Fraunhofer Institute for Material and Beam Technology | Biemelt T.,TU Dresden | Helmer A.,Fraunhofer Institute for Material and Beam Technology | And 5 more authors.
Advanced Functional Materials | Year: 2015

Hierarchical porous carbon (HPC, DUT-106) with tailored pore structure is synthesized using a versatile approach based on ZnO nanoparticles avoiding limitations present in conventional silica hard templating approaches. The benefit of the process presented here is the removal of all pore building components by pyrolysis of the ZnO/carbon composite without any need for either toxic/reactive gases or purification of the as-prepared hierarchical porous carbon. The carbothermal reduction process is accompanied by an advantageous growing of distinctive micropores within the thin carbon walls. The resulting materials show not only high internal porosity (total pore volume up to 3.9 cm3 g-1) but also a large number of electrochemical reaction sites due to their remarkably high specific surface area (up to 3060 m2 g-1), which renders them particularly suitable for the application as sulfur host material. Applied in the lithium-sulfur battery, the HPC/sulfur composite exhibits a capacity of >1200 mAh g-1-sulfur (>750 mAh g-1 electrode) at a high sulfur loading of ≤3 mg cm-2 as well as outstanding rate capability. In fact, this impressive performance is achieved even using a low amount of electrolyte (6.8 μl mg-1 sulfur) allowing for further weight reduction and maintenance of high energy density on cell level. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.

Muller-Meskamp L.,TU Dresden | Kim Y.H.,TU Dresden | Roch T.,TU Dresden | Hofmann S.,TU Dresden | And 4 more authors.
Advanced Materials | Year: 2012

Direct laser interference patterning (DLIP) is used to fabricate large area, two-dimensional periodic surface patterns on polyethylene terephthalate (PET) substrates to enhance the performance of ZnPc:C60 solar cells by light concentration in the absorber layer. Comparing the power conversion efficiencies to the reference cell on flat PET, a relative increase of 21% is observed for the hexagonal pattern with 0.7 μm period, depicted in the figure. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Perez-Hernandez H.,Fraunhofer Institute for Material and Beam Technology
Biointerphases | Year: 2012

Micropatterned surfaces with cell adhesive areas, delimited by protein repellent microstructures, are in high demand for its potential use as relevant biological assays. This is not only because such surfaces allow directing cell growth in a spatially localized and restricted manner, but also because they can be used to elucidate basic cell growth and orientation mechanisms. Here, it is presented a laser-assisted micropatterning technique to fabricate large area microstructures of poly (ethylene glycol) hydrogel onto a cell adhesive surface: a biofunctional maleic anhydride copolymer. By varying photoinitiator, laser intensity, copolymer as well as the hydrogel layer thickness, the optimum conditions to produce high quality features were found. The suitability of these micropatterned substrates for bioassay applications was proved by cell adhesion studies. The introduced procedure could be used to prepare a broad range of microarrays for certain bioanalytical approaches and to create different types of biofunctional surfaces.

Berger L.-M.,Fraunhofer Institute for Material and Beam Technology
International Journal of Refractory Metals and Hard Materials | Year: 2015

Thermally sprayed hardmetal coatings have a typical thickness within the range 100-500 μm. Thus, thermal spray enables the functionality of hardmetals to be realized on the surface of large parts, which cannot be produced by powder metallurgy for technical and economical reasons. This article reviews the different types of thermal spray processes, with particular focus on the high velocity HVOF and HVAF deposition techniques which are ofmost relevance to the application of hardmetal coatings. Feedstock powder preparation technologies are presented. The majority of hardmetal thermal spray coatings are based either onWC or Cr3C2 or hard phases appearing as a result of their interaction. As an alternative, TiC-based compositions aremost intensively studied. Thermal spraying generates significant changes in the hardmetal chemical and phase compositions between the feedstock powder to the sprayed coating. Coating formation and microstructures as well as selected properties, such as hardness, the effect of heat treatments and the oxidation in service, as well as corrosion resistance are discussed. As an example for wear protection applications, abrasion wear resistance is shortly discussed. This paper is a partly updated and condensed version of the chapter: "Coatings by thermal spray" in the book "Comprehensive Hard Materials", V.K. Sarin (Editor-in-Chief) & D. Mari & L. Llanes (Vol. Ed.), Vol. 1 (pp. 471-506), Elsevier, 2014. © 2014 Elsevier Ltd.

Bauer I.,Fraunhofer Institute for Material and Beam Technology | Kohl M.,Fraunhofer Institute for Material and Beam Technology | Althues H.,Fraunhofer Institute for Material and Beam Technology | Kaskel S.,Fraunhofer Institute for Material and Beam Technology
Chemical Communications | Year: 2014

A sodiated Nafion-coating on a porous polypropylene backbone was used as a cation selective separator for room temperature sodium-sulfur batteries. The capacity of the cells after 20 cycles could be enhanced by 75% to 350 mA h gsulfur -1 using the new separator. © The Royal Society of Chemistry 2014.

Schneider D.,Fraunhofer Institute for Material and Beam Technology
IEEE International Ultrasonics Symposium, IUS | Year: 2012

The test method LAwave® measures the dispersion of surface acoustic waves induced by short laser pulses. The technique uses that the propagation velocity of the wave depends on the frequency in coated and surface modified materials. Measuring the dispersion of the surface acoustic wave enables to determine important properties of the material surface. Two examples demonstrate that the laser-acoustic method can solve very different problems of surface engineering. The wear resistance of diamond-like carbon films with a thickness of few nano-meters was evaluated. The depth of sub-surface damage layers in semi-conductor materials was determined, which are created when wafers are sliced from the ingot. © 2012 IEEE.

Lasagni A.F.,Fraunhofer Institute for Material and Beam Technology | Menendez-Ormaza B.S.,Fraunhofer Institute for Material and Beam Technology
Advanced Engineering Materials | Year: 2010

In this study, we present different approaches for the fabrication of two and three dimensional structures using two-beam interference lithography. The advantages of using more than one irradiation step for the fabrication of complex structures are theoretically demonstrated by avoiding the introduction of line effects. For the fabrication of 3D structures, two alternatives are discussed including a layer by layer approach as well as a multidimensional (non-orthogonal) interference exposure setup. Finally, an example of biomimetic patterning is given. In all cases, numerical calculations showed a good agreement with the experimental results, being able to explain the shape of the fabricated structures. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Schultrich B.,Fraunhofer Institute for Material and Beam Technology
Diamond and Related Materials | Year: 2011

The structure of tetrahedral bonded amorphous carbon (ta-C) is determined by the energy of the impinging carbon ions, the angle of incidence, the substrate temperature and the deposition rate. Up to now modeling of the ta-C growth was concentrated on the energy effects by investigating the early stages of the ion impact and the short-time relaxation in the thermal spike. A new analytical model is presented, which emphasizes the role of long-time diffusion, driven by the stress induced drift towards the surface. In accordance with the experimentally found trends, the model allows the estimation of the sp 3 content in dependence on the technological relevant deposition parameters ion energy, angle, temperature, rate and their distributions. This opens the way for the realistic simulation of ta-C growth in industrial coaters. © 2011 Elsevier B.V. All rights reserved.

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