Yazar "Colijn, Hendrik" seçeneğine göre listele

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    Evaluation of thermal conductivity of GNPs-doped B4C/Al-Si composites in terms of interface interaction and electron mobility
    (Elsevier Science Sa, 2019) Polat, Safa; Sun, Yavuz; Cevik, Engin; Colijn, Hendrik
    The examination of the interactions between graphene and other components commonly used in thermal applications is an important approach for the development of materials with high thermal conductivity. For this purpose, graphene-doped boron carbide reinforced Al Si matrix composites were produced using semi-powder and pressure infiltration methods together. These composites were then characterized by SEM, TEM and XRD analysis. Thermal conductivity coefficients of these composites were determined experimentally by Laser Flash method. In order to examine the effect of phonon transfer on the experimental data, the interacting components were simulated, and the interfacial thermal conductivity was calculated with the acoustic mismatch model. Then, theoretical thermal conductivity of composites was calculated by Hasselman-Johnson model and Maxwell's approach. The electrical conductivity of the composites was measured by four-point probe method for electron mobility. As a result, experimental results were found to be slightly lower than the theoretical ones. This was affected by several different factors but the most important one is thought to be related to porosity.
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    Investigation of wear and corrosion behavior of graphene nanoplatelet-coated B4C reinforced Al-Si matrix semi-ceramic hybrid composites
    (Sage Publications Ltd, 2019) Polat, Safa; Sun, Yavuz; Cevik, Engin; Colijn, Hendrik; Turan, M. Emre
    The present study aims to produce graphene nanoplatelet-coated B4C ceramic particle using semi-powder method and to investigate the effect of graphene nanoplatelets on wear and corrosion performance of Al-Si-based metal matrix hybrid composites. For this purpose, first graphene nanoplatelets at different ratios (0.25, 0.5, and 1 vol.%) were coated to the surfaces of B4C particles and then the Al-Si alloy was infiltrated into the reinforcements by gas pressure infiltration method. The characterization of graphene nanoplatelet-coated B4C powders and its composites was carried out by X-ray diffraction, differential scanning calorimetry, scanning electron microscope, and transmission electron microscope analysis. Tribological properties were investigated by reciprocating ball-on-flat method under three different loads (10-20-40 N) in a dry environment. The corrosion resistance was carried out with Tafel polarization method in 3.5% NaCl solution. Characterization results show that graphene coated on the B4C surface was successfully achieved by semi-powder method. After infiltration process, a new phase formation was not observed, but porosity increased with the increase of graphene content. When the boron carbide surface was coated with 0.5vol.% graphene, it was determined that the specific wear resistance increased by 55% and the corrosion resistance decreased by 12%.
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    Microstructure and synergistic reinforcing activity of GNPs-B4C dual-micro and nano supplements in Al-Si matrix composites
    (Elsevier Science Sa, 2019) Polat, Safa; Sun, Yavuz; Cevik, Engin; Colijn, Hendrik
    The aim of this study is to investigate the mechanical effect of graphene nanoparticles and boron carbide microparticles together on Al-17Si alloy. For this purpose, graphene nanoparticles were firstly attached to boron carbide surfaces by semi-powder method. The Al-17Si alloy was then infiltrated into these particles. Systematic characterization of produced composites, microstructure investigations, strengthening mechanisms were investigated respectively. The composites were systematically characterized by XRD, DSC, SEM and TEM. Their mechanical strength was determined experimentally by compression test. In addition, the contribution of these reinforcements to strength by using some models has been calculated theoretically and the results have been associated with the microstructure. According to these results, the yield strength of pure matrix was increased from 185 MPa to 547 MPa by increasing 195% with the reinforcement of 0.5 vol% GNPs thorn B4C at most. This result is also the case where the theoretical and experimental are the most compatible. In this case, it is thought that load transfer mechanism and dislocations make the most positive contribution while porosity makes the most negative effect. (C) 2019 Elsevier B.V. All rights reserved.