Machinable α-SiAlON/BN Composites

Dense machinable α-SiAlON/BN composites were fabricated by hot-pressing using turbostratic boron nitride (tBN) obtained from nitridation of melamine diborate. The tBN was added to the starting powders, or introduced as a coating that formed in situ on α-Si3N4 carrier powders during nitridation, and was subsequently converted to hexagonal boron nitride (hBN) during hot pressing by solution reprecipitation. These composites maintain high strength at 1000°C and their strength/hardness are much higher than similar composites prepared using commercial hBN powder, which yielded a coarser microstructure. Good machinability was achieved despite a flat R curve. Comments Copyright The American Ceramic Society. Reprinted from Journal of the American Ceramic Society, Volume 89, Issue 7, 2006, pages 2147-2153. This journal article is available at ScholarlyCommons: http://repository.upenn.edu/mse_papers/104 Machinable a-SiAlON/BN Composites Roman Shuba and I-Wei Chen Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6272 Dense machinable a-SiAlON/BN composites were fabricated by hot-pressing using turbostratic boron nitride (tBN) obtained from nitridation of melamine diborate. The tBN was added to the starting powders, or introduced as a coating that formed in situ on a-Si3N4 carrier powders during nitridation, and was subsequently converted to hexagonal boron nitride (hBN) during hot pressing by solution reprecipitation. These composites maintain high strength at 10001C and their strength/hardness are much higher than similar composites prepared using commercial hBN powder, which yielded a coarser microstructure. Good machinability was achieved despite a flat R curve.