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    Effect of boron carbide additive and sintering temperature - Dwelling time on silicon carbide properties
    (Elsevier Sci Ltd, 2021) Yasar, Zeynep Ayguzer; DeLucca, Vincent A.; Haber, Richard A.
    Sintering temperature and composition are two important factors that affect the properties of ceramic materials. In this study, the effects of sintering temperature, dwelling time, intermediate dwell, and B4C content on the density, microstructure, and elastic properties of dense SiC ceramics were investigated. 1.5 wt% C and 0.25 wt% or 0.5 wt% B4C were added to SiC which was spark plasma sintered (SPS) at 1900 degrees C, 1950 degrees C, or 2000 degrees C under a pressure of 50 MPa in flowing argon with an intermediate dwell at 1400 degrees C (for 1 or 30 min). The results of the sintering study showed that the best microstructure was obtained in the sample sintered at 1900 degrees C for 10 min with an intermediate dwell at 1400 degrees C for 30 min. Under these conditions, the sintered sample has reached full density (>99%) with elastic, shear and bulk modulus values of 436 GPa, 184 GPa and 233 GPa, respectively. In addition, it was observed that 0.5 wt% B4C content gave preferred results over 0.25 wt% B4C content. These conditions allow the production of fully dense silicon carbide ceramics with fine-grained microstructure.
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    Öğe
    Effect of Carbon Addition and Mixture Method on the Microstructure and Mechanical Properties of Silicon Carbide
    (Mdpi, 2020) Yasar, Zeynep Ayguzer; Haber, Richard A.
    High dense (>99% density) SiC ceramics were produced with addition of C and B4C by spark plasma sintering method at 1950 degrees C under 50 MPa applied pressure for 5 min. To remove the oxygen from the SiC, it was essential to add C. Two different mixture method were used, dry mixing (specktromill) and wet mixing (ball milling). The effect of different levels of carbon additive and mixture method on density, microstructure, elastic modulus, polytype of SiC, Vickers hardness, and fracture toughness were examined. Precisely, 1.5 wt.% C addition was sufficient to remove oxide layer from SiC and improve the properties of dense SiC ceramics. The highest hardness and elastic modulus values were 27.96 and 450 GPa, respectively. Results showed that the 4H polytype caused large elongated grains, while the 6H polytype caused small coaxial grains. It has been observed that it was important to remove oxygen to achieve high density and improve properties of SiC. Other key factor was to include sufficient amount of carbon to remove oxide layer. The results showed that excess carbon prevented to achieve high density with high elastic modulus and hardness.
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    Öğe
    Evaluating the role of uniformity on the properties of B4C-SiC composites
    (Elsevier Sci Ltd, 2021) Yasar, Zeynep Ayguzer; Haber, Richard A.
    Fully dense boron carbide-silicon carbide composites were successfully produced by spark plasma sintering method at 1950 degrees C under 50 MPa applied pressure. The effect of dry and wet mixing methods on uniformity was observed. Density, elastic modulus, microstructure, Vickers hardness and fracture toughness were evaluated. The results showed that dry mixing did not provide uniformity on composites properties. On the other hand wet mixing provided uniformity in microstructure and consistency in material properties. The hardness of the sample containing 50 wt% B4C was measured to be 30.34 GPa hardness value was found at 50 wt% B4C content sample. The increase in the B4C content of the composites decreased the Young's modulus, shear modulus, bulk modulus and fracture toughness. The highest values were found at 10 wt% B4C sample which were 415 GPa (E), 177 GPa (G), 209 GPa (K), and 2.89 MPa m(1/2) fracture toughness (Ka(Ic)).