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Abstract: Cubic boron nitride (cBN) powder was coated with Ni nanoparticle and SiO2 nanolayer (abbreviated as cBN/Ni and cBN/SiO2, respectively) by rotary chemical vapor deposition (RCVD), and compacted with SiO2 powder by spark plasma sintering at 1473–1973K for 0.6ks. The effects of Ni and SiO2 coatings on the densification, phase transformation of cBN and hardness of SiO2–cBN composites were compared. The phase transformation of cBN to hBN was identified at 1973K in SiO2–cBN/SiO2 composites, 300K higher than that in SiO2–cBN/Ni composites, indicating that SiO2 retarded the transformation of cBN. The relative density of SiO2–cBN/SiO2 with 50vol% cBN sintered at 1873K was 99% with a hardness of 14.5GPa. [Copyright &y& Elsevier]

Abstract: Transparent SiO2 bodies were prepared by pressureless sintering (PLS) and spark plasma sintering (SPS). The effects of sintering and annealing temperature on the transmittance of the SiO2 bodies were investigated. The SiO2 bodies sintered by SPS and PLS at 1073–1573K were amorphous. With increasing the sintering temperature to 1673K, the SiO2 bodies sintered by PLS were crystallized while those sintered by SPS were still amorphous. The relative density of the SiO2 bodies sintered by SPS was 98.5% at 1373K and 100% at 1573K, whereas that sintered by PLS was 92.6% at 1373K and 98.9% at 1573K. The transmittance was 91.0% and 81.5% at a wavelength (λ) of 2μm for the SiO2 sintered bodies by SPS and PLS, respectively. In the ultraviolet range, the transmittance of the SiO2 bodies sintered by SPS at 1573K was about 40% at λ =200nm and increased to 75% after annealing at 1073K for 1h, which was about three times of the transmittance of the SiO2 bodies sintered by PLS (24.8%). [Copyright &y& Elsevier]

Abstract: SiO2–cBN composites were consolidated by spark plasma sintering at 1473–1973K. The effects of cBN content and sintering temperature on the relative density, phase transformation, microstructure and mechanical properties of the SiO2–cBN composites were investigated. The relative density of the SiO2–cBN composites increased with increasing SiO2 content. The phase transformation of cBN to hBN in SiO2–cBN composites was identified at 1973K, showing the highest transformation temperature in cBN-containing composites. The SiO2–20vol% cBN composites sintered at 1673K showed the highest hardness and fracture toughness of 12.5GPa and 1.5MPam1/2, respectively. [Copyright &y& Elsevier]