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Grenchen, Switzerland

Klunsner T.,Materials Center Leoben Forschung | Zielbauer F.,Materials Center Leoben Forschung | Marsoner S.,Materials Center Leoben Forschung | Deller M.,Fritz Schiess AG | And 2 more authors.
International Journal of Refractory Metals and Hard Materials | Year: 2016

Galling, i.e. the transfer of workpiece material to tool surfaces, is an important factor known to influence both wear behaviour and loading conditions of metalworking tools such as deep-drawing, blanking or fine blanking punches or dies. The current study investigates very early stages of galling of mild steel on WC-Co hard metals coated by AlCrN-based hard coatings. Repeated dry-sliding contacts with virgin steel material were physically simulated by a ball-on-disc test setup with a virgin contact area on the ball in each lap. Special attention was paid to the influence of coating surface topography produced by coating post-treatment and the resulting distinct differences in galling behaviour. Galling initiation is illustrated by cross-sections of micrometre-sized features of transferred steel, showing their nucleation sites to be microscopic surface asperities. A layer-by-layer material transfer mechanism is indicated by the galling features' internal layered structure. The current work demonstrates a clear connection between the ratio of peaks to valleys on coating surfaces and the kinetics of the early stages of galling. A reduction of this ratio, e.g. by coating post-treatment via blasting with diamond-containing elastomer particles, leads to a reduced tendency for steel transfer to coated WC-Co hard metal surfaces. © 2016 Elsevier Ltd. All rights reserved. Source


Klunsner T.,Materials Center Leoben Forschung | Morstein M.,PLATIT AG Advanced Coating Systems | Marsoner S.,Materials Center Leoben Forschung | Deller M.,Fritz Schiess AG | Marklein B.,Robert Bosch GmbH
International Journal of Refractory Metals and Hard Materials | Year: 2016

WC-Co hard metals are materials widely used in wear applications, metal machining and highly fatigue loaded tools. Shaping tools and components made of hard metals often requires electrical discharge machining (EDM) that is well-known to negatively influence the material's fatigue properties. The current work demonstrates that it is possible to achieve a fatigue limit of electrical discharge machined specimens equal to the one of finely ground and polished reference samples. This is achieved by the application of advanced wire EDM technology combined with a sole surface post-treatment step of abrasive blasting. Stress amplitude-life curves were determined in a four point bending test setup. Depth profiles of residual stress were determined by means of X-ray diffraction for electrical discharge machined samples prior to and after blasting. Surface defect size was documented in metallographic cross sections by scanning electron microscopy. The surface residual stress state was found to be crucially important regarding the observed fatigue behavior. If the applied EMD technology produces cracks shallow enough to allow for their removal by abrasive blasting and compressive residual stress is introduced as deep into the surface as damage reaches, the negative effect of EDM on the fatigue limit is neutralized. © 2016 Elsevier Ltd. Source


Best J.P.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Zechner J.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Zechner J.,KAI Kompetenzzentrum Automobil und Industrie Elektronik GmbH | Shorubalko I.,Empa - Swiss Federal Laboratories for Materials Science and Technology | And 4 more authors.
Scripta Materialia | Year: 2016

While small-scale fracture toughness measurements provide an extremely useful material parameter, notch preparation and ion-beam damage continue to be contentious issues. Herein we utilize a conventional gallium source for notching ceramic cantilevers, and compare against notches fabricated using xenon and helium ions from commercial focused ion microscopes. This is the first time ions other than gallium have been used for notches in such measurements. We observe some statistical dependence of the measured toughness on the utilized notching ion, bringing into question the influence of ion-material interactions in creating residual stresses or embrittlement in the small volumes around the notch root. © 2015 Elsevier Ltd. All rights reserved. Source


Karimi A.,Ecole Polytechnique Federale de Lausanne | Morstein M.,PLATIT AG Advanced Coating Systems | Cselle T.,PLATIT AG Advanced Coating Systems
Surface and Coatings Technology | Year: 2010

Multi-element oxynitrides of type Al-Cr-Si-O-N were prepared using r.f. magnetron sputtering from Al80Cr2.5Si17.5 (at.%) target composition and O2/(O2+N2) gas flow ratio between 0 and 100%. Two series of samples varying from pure nitrides to pure oxides and deposited at 400°C and 650°C were investigated by (WDS EPMA)+SIMS, XRD, SEM, and nanoindentation measurements. Chemical analysis revealed that the incorporation of oxygen into the films increases much faster than the fraction of oxygen in the gas flow so that the oxide phases can be formed from the gas ratio of about O2/(O2+N2)=20%. Addition of oxygen gradually alters the crystallinity of nitride phases due to the incorporation of interstitial atoms and the formation of metal vacancies, but nitride lattices seem to survive up to the overall oxygen incorporation of about 40% into the film. Up on supplying more oxygen flow, the amorphisation of films continues by absorbing more oxygen atoms up to the range of O2/(O2+N2)≈80% to 90%. Beyond that limit, the formation of crystalline α-Al2O3 was observed, probably stimulated by the presence of α-Cr2O3 and SiO2 in the films. Transition from nitride to oxide has strong consequences on film hardness, which changes from 30-33GPa for nitrides to 12-13GPa for amorphous layers, and increases again to 20-25GPa for pure oxides. © 2010 Elsevier B.V. Source


Wheeler J.M.,Empa Swiss Federal Laboratories for Materials Testing and Research | Raghavan R.,Empa Swiss Federal Laboratories for Materials Testing and Research | Chawla V.,Empa Swiss Federal Laboratories for Materials Testing and Research | Morstein M.,PLATIT AG Advanced Coating Systems | Michler J.,Empa Swiss Federal Laboratories for Materials Testing and Research
Surface and Coatings Technology | Year: 2014

The elevated temperature performance of a wide range of chromium nitride-based hard coatings was evaluated using in situ micro-compression in the scanning electron microscope. This allows the first direct measurement of the high temperature compressive strength, rather than the hardness, of such coatings. The microstructure of the coatings was analyzed using X-ray diffraction and focused ion beam cross sectioning followed by electron microscopy. Micropillars were examined using electron microscopy before, during and after compression. Trends in deformation behavior and failure stress with temperature are discussed in relation to the coatings' microstructures and their room temperature mechanical properties. © 2014 Elsevier B.V. Source

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