Al2O3–cBN composites sintered by SPS and HPHT methods

Abstract Spark Plasma Sintering (SPS) and High Pressure–High Temperature (HPHT) methods were chosen in order to study the behaviour of metastable cubic boron nitride (cBN) during sintering of Al 2 O 3  + 30 vol.% cBN composites at low and high pressure. Relatively low sintering temperatures were used to avoid the undesired reverse transformation of cBN to hexagonal, graphite-like form. The microstructure, and phase composition as well as physical and mechanical properties of the resulting Al 2 O 3 –cBN composites were investigated. In the ball-on-disc tests, the coefficient of friction and the specific wear rate of the sintered samples were determined by rotating the sample against a stationary alumina ball. The best composites obtained by SPS (at 1300 °C/75 MPa) had slightly lower density, Young's modulus and hardness than those obtained by HPHT but their wear resistance was much better. Formation of hBN was suppressed up to 1300 °C during SPS consolidation at the pressure of 75 MPa.