Densification and microstructure of Al2O3-cBN composites prepared by spark plasma sintering

Al2O3-cubic boron nitride (cBN) composites were prepared from Al2O3 and cBN powders by spark plasma sintering (SPS) at temperatures of 1200 to 1600 degrees C for 600 s under a pressure of 100 MPa. Densification, phase transformation, microstructure and mechanical properties of the Al2O3 cBN composites were investigated. Fully dense Al2O3-cBN composites containing 10 to 20 vol% cBN with a relative density of more than 98% were obtained at 1300 degrees C for 600 s without the phase transformation from cBN to hexagonal BN (hBN). The transformation of cBN was more greatly accelerated in the Al2O3-cBN composite than in cBN. The cBN phase to Al2O3 inhibited the grain growth of Al2O3 in the Al2O3-cBN composite. Vickers hardness of dense Al2O3-cBN composites containing 10 to 20 vol% cBN sintered at 1300 degrees C showed the maximum value of 26 GPa. The Al2O3-cBN composite containing 20 vol% cBN sintered at 1300 degrees C had the highest fracture toughness of 4.1 MPa.m(1/2). (c) 2008 The Ceramic society of Japan. All rights reserved.