Papers by Author: Omer Van der Biest

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Authors: Bram Neirinck, Jan Fransaer, Jef Vleugels, Omer Van der Biest
Abstract: From an environmental, safety and economic perspective water should be the solvent of choice for electrophoretic deposition under industrial circumstances. However, because of the electrolytic decomposition of water under the influence of direct current, the majority of EPD is carried out in non-aqueous solvents. In this work, experiments prove that deposits can be obtained from aqueous alumina suspensions while avoiding electrolysis of the medium by using unbalanced alternating current fields [1]. In addition it is shown that the formed deposits have a green density which is intrinsically higher than those formed by traditional DC EPD from ethanol based suspensions. A theoretical basis for both electrophoretic deposition by means of unbalanced alternating fields and the higher density of deposits formed by application of such fields is provided.
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Authors: Bernd Baufeld, Hans Joachim Rätzer-Scheibe, Omer Van der Biest
Abstract: Electrophoretic deposition (EPD) allows the fabrication of ceramic coatings at lower cost and higher speed than most other deposition techniques. The processing consists of powder deposition from a suspension under the influence of an electric field and subsequent consolidation of the coating by sintering. Adherent zirconia coatings with coating thicknesses up to 0.1 mm were obtained from different suspensions, one methyl-ethyl-ketone and the other ethanol based. The standard sintering temperature is 1200°C, which easily may damage or change the substrate and also means high production costs. In order to reduce the sintering temperature, suspensions with the addition of ZrN were investigated. Due to reaction bonding, sintering in air at a remarkable low temperature of 1000°C was successful. The elastic modulus of the EPD coatings has been derived from impulse excitation experiments and the thermal conductivity from laser flash analysis. The elastic modulus was about 22 GPa and the thermal conductivity between 0.4 and 0.6 W/(m•K) at room temperature, both decreasing slightly with temperature. Especially the exceptionally low thermal conductivity makes EPD coatings a promising candidate for thermal barrier coatings.
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Authors: Shui Gen Huang, Omer Van der Biest, Jef Vleugels, Kim Vanmeensel, Lin Li
Abstract: In this study, 2 mol% Y2O3 (2Y), 1 mol% Y2O3+6 mol% CeO2 (1Y6Ce) and 12 mol% CeO2 (12Ce)-doped tetragonal ZrO2 ceramics were made by spark plasma sintering (SPS) for 2 min at 1450°C under a pressure of 60 MPa. The influence of stabilizers on microstructure, phase and mechanical properties of the ZrO2 ceramics was investigated. After sintering, the 2Y and 1Y6Ce were intact, containing full tetragonal ZrO2 phase on the polished cross-sectioned surface, whereas the 12Ce exhibited macro-cracks, corresponding to a large amount of monoclinic ZrO2 phase. Graded microstructure and mechanical properties were observed in the 1Y6Ce, showing a gradually decreased fracture toughness from sample edge towards centre, together with the slight decreased hardness. The 2Y had a uniform microstructure and mechanical properties. The formation of the graded structure and toughness profile was explained in terms of the gradual CeO2 reduction to Ce2O3 in the Y2O3+CeO2 doped ZrO2 ceramics.
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Authors: Jef Vleugels, Omer Van der Biest
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Authors: Chao Zhao, Gert Roebben, Marc M. Heyns, Omer Van der Biest
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Authors: Michael M. Gasik, Bao Sheng Zhang, Omer Van der Biest, Jef Vleugels, Guy Anné, Stijn Put
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Authors: T. Lauwagie, K. Lambrinou, Iulian Mircea, Marion Bartsch, W. Heylen, Omer Van der Biest
Abstract: Cylindrical specimens made of the Ni-based super-alloy Inconel 625 (IN 625) were coated with (a) NiCoCrAlY, or (b) NiCoCrAlY and yttria-stabilised zirconia (YSZ: in this case, zirconia with 7-8 wt% yttria), using the electron beam - physical vapor deposition (EB-PVD) technique. In the bi-layer coatings, the YSZ layer is the thermal barrier coating (TBC) and the NiCoCrAlY layer is the metallic bond coat (BC). The BC improves the bonding between the substrate and the ceramic TBC, while the low thermal conductivity of the TBC o ers high-temperature protection to the substrate. This paper focuses on the determination of the elastic moduli of the substrate and the coating layers of the test samples. The elastic moduli of the three di erent materials (IN 625, NiCoCrAlY and YSZ) were determined by means of a mixed numerical - experimental technique (MNET). The employed MNET was based on the comparison of the experimentally measured resonant frequencies of the rst bending mode of the test samples to the numerically calculated ones. The unknown elastic properties were determined by ne-tuning the elastic material parameters of the numerical models so as to enable the reproduction of the experimentally measured resonant frequencies.
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Authors: Bernd Baufeld, Omer Van der Biest
Abstract: In order to obtain a protection against temperature and stress induced detrimental rumpling of the metal surface of turbine blades, thin ceramic coatings are suggested. As a cheap and fast method for the fabrication of a ceramic zirconia coating, electrophoretic deposition on a Ni based superalloy is described. Crack free, 0.15 mm thick coatings with homogenous morphology were obtained. The Young’s modulus and the damping property of the ceramic coating, derived from the impulse excitation technique, are investigated as a function of the temperature up to 1000°C.
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Authors: Koenraad Bonny, Patrick de Baets, Omer Van der Biest, Jef Vleugels, Bert Lauwers
Abstract: A trend in the development of WC based cemented carbides and zirconia based ceramic composites is grain size refinement and more narrow grain size distributions of the starting powder, in order to accomplish higher hardness and abrasive wear resistance. The current work reports the results of dry sliding wear experiments on laboratory-made electrically conductive ZrO2-WC composites and commercially available WC-Co based cemented carbides, which have been manufactured and finished by rough cutting wire EDM with consecutive execution of gradually finer EDM regimes. Tribological data are obtained using a small-scale pin-on-plate test rig. Wear tracks are analyzed by surface scanning topography and scanning electron microscopy, revealing that the outer extensions of the wear tracks exhibit some differences in wear behavior compared to the central parts.
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Authors: Laura Fè, F. Vasiliu, Gerd J. Norga, Dirk J. Wouters, Omer Van der Biest
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