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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]

Abstract: Al2O3–cBN/Ni composites were consolidated by spark plasma sintering (SPS) using α-Al2O3 and Ni nanoparticle precipitated cBN (cBN/Ni) powders. The Ni nanoparticles, 10–100nm in diameter and 0.5–2.2mass% in content, were precipitated on cBN powder by rotary chemical vapor deposition. The effect of sintering temperature (T SPS) and Ni content (C Ni) on the densification, phase transformation, microstructure and hardness of the Al2O3–cBN/Ni composites were investigated. The highest relative density of Al2O3–30vol% cBN composite was 99% at T SPS =1573K and C Ni =1.7mass%. At T SPS =1673K, the relative density decreased due to the phase transformation of cBN to hBN. The Vickers hardness of Al2O3–30vol% cBN/Ni at T SPS =1573K and C Ni =1.7mass% showed the highest value of 27GPa. [Copyright &y& Elsevier]