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The sintering behaviours, phase compositions, microstructures, and mechanical properties of Al 2 O 3 -based matrix composites reinforced with up to 20 vol% of cubic boron nitride (cBN, super-hard phase) were investigated. The materials were prepared via the method of spark plasma sintering (SPS). Additionally, pure cBN powder was treated under identical SPS conditions for the purpose of comparison. The temperatures at which hexagonal boron nitride (hBN, graphite-like phase) was detected in pure cBN and in cBN dispersed in the Al 2 O 3 + 10 TiN matrix were 1600 °C and 1300 °C, respectively. The presence of additives in the Al 2 O 3 matrix had a pronounced influence on the formation of hBN, with TiN > ZrO 2 > pure Al 2 O 3. All the composites exhibited quite good improvements in fracture toughness, of about 1.5 MPa·m1/2 on average over that of Al 2 O 3. Crack deflection on cBN grains was identified as the main toughening mechanism of the ceramics investigated. Unlabelled Image • Composites containing cubic boron nitride (cBN) have been sintered at low pressure. • Spark plasma sintering (SPS) method allows to obtain full dense composite at 1300 °C. • Al 2 O 3 -based composites with cBN have better fracture toughness than pure Al 2 O 3. • During SPS pure cBN is more stable then cBN dispersed in ceramic matrix. • TiN promotes of graphite-like, hexagonal boron nitride formation most extensively. [ABSTRACT FROM AUTHOR]