Al₂O₃-cBN composites sintered by SPS and HPHT methods

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 Al₂O₃ +30vol.% 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 Al₂O₃-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/75MPa) 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 75MPa.