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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]