Papers by Author: Omer Van der Biest

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Authors: B. Basu, R.G. Vitchev, Jef Vleugels, J.P. Celis, Omer Van der Biest
Authors: Stijn Put, Jef Vleugels, Guy Anné, Omer Van der Biest
Authors: Stijn Put, Guy Anné, Jef Vleugels, Omer Van der Biest
Authors: C. Zhao, Jef Vleugels, L. Vandeperre, B. Basu, Omer Van der Biest
Authors: Koenraad Bonny, Patrick de Baets, Omer Van der Biest, Jef Vleugels, Bert Lauwers
Abstract: WC-Co based cemented carbides are widely used in technical applications, in which they are exposed to complex thermo-mechanical loadings. Previous research work has demonstrated that these materials exhibit a lifetime-limiting fatigue sensitivity at room temperature. This investigation is focused on the influence of heating as a result of friction of pin-on-plate tribocouples. WC-Co samples have been manufactured and surface finished by wire-EDM and grinding. Reciprocative dry friction experiments are performed under various loading conditions and sliding velocities. Correlations are established between the bulk temperature rise of the test samples and the imposed test conditions, material properties, surface conditions and coefficient of friction. Topographies and cross-section views of the tested samples were examined by SEM, revealing temperature dependent wear mechanisms, including binder phase modification.
Authors: Shui Gen Huang, Lin Li, Jef Vleugels, Pei Ling Wang, Omer Van der Biest
Abstract: Mixtures of 12 mol% CeO2-stabilised ZrO2 with 5 to 20 wt % Al2O3 were prepared and densified through pressureless sintering in air at 1450° C for 1 to 4 h. The influence of the Al2O3 content and sintering time on the phase constitution, microstructure and mechanical properties of the as-sintered composites were investigated. Fully dense Ce-TZP/Al2O3 ceramics with a good combination of hardness and fracture toughness can be obtained by pressureless sintering in air for only 1 h. The addition of Al2O3 to Ce-TZP improves the mechanical properties and suppresses ZrO2 grain growth. The average ZrO2 grain size increases with increasing sintering time and decreasing Al2O3 content. This leads to an increase in toughness. An excellent fracture toughness of 14.3 MPam1/2 in combination with a Vickers hardness of 9.14 GPa was obtained for 12 mol % CeO2-TZP with 5 wt % Al2O3, sintered for 4 h.
Authors: Guy Anné, Bram Neirinck, Kim Vanmeensel, Omer Van der Biest, Jef Vleugels
Abstract: A model was developed to explain the magnitude of the potential drop over the deposit for non-conductive powders during electrophoretic deposition (EPD). The magnitude of the potential drop over the deposit is explained in terms of a reduced ion transport through the deposit, as controlled by the pore potential that is related to the thickness of the electrostatic double layer relative to the pore radius and the magnitude of the surface potential of the powder particles. This model was validated for EPD of Al2O3 powder from ethanol-based suspensions with HNO3 addition. The specific resistivity of the deposit could be related to the calculated potential in the pores of the deposit.
Authors: Koenraad Bonny, Patrick de Baets, Omer Van der Biest, Jef Vleugels, Bert Lauwers
Abstract: Zirconia-based ceramic composites such as ZrO2-WC, ZrO2-TiCN and ZrO2-TiN, are suitable for wire-EDM, due to their sufficiently electro-conductive secondary phases inside. Thus, the material removal technique of EDM to shape complex geometry materials economically and with high accuracy, irrespective of mechanical properties, could be successfully employed on these ceramics. Samples of these ZrO2-based ceramics were developed in laboratory and manufactured and surface finished by wire-EDM. Reciprocative dry sliding pin-on-plate experiments revealed that the ZrO2-WC composite exhibits better tribological characteristics in comparison with the composites of ZrO2-TiCN and ZrO2-TiN. Furthermore, topographies and cross-sectional views of worn surfaces were analyzed by SEM, revealing that the secondary phase inside the investigated composites governs the wear mechanism.
Authors: Koenraad Bonny, Patrick de Baets, Omer Van der Biest, Jef Vleugels, Bert Lauwers
Abstract: At present, cobalt is the most commonly used binder material in tungsten carbide based hardmetals. Current research on sliding wear performance of these cemented carbides, however, reveals promising results for nickel binder as well. Test samples of WC-Co and WC-Ni hardmetals have been machined and surface finished by wire-EDM and grinding. From comparative dry sliding pin-on-plate experiments on wire-EDM’ed, ground and polished grades, correlations are derived between wear volume loss and friction on the one hand and contact pressure, sliding distance, binder phase and microstructure on the other hand. The lowest wear levels are encountered with polished cemented carbides. The EDM induced surface modification turns out to deteriorate wear resistance, especially during the running-in stage of sliding. These findings are in agreement with Xray diffraction measurements of the residual stress level in the WC phase.
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