PHASE-RELATIONSHIPS AND RELATED MICROSTRUCTURAL OBSERVATIONS IN THE CA-SI-AL-O-N SYSTEM

A systematic set of samples with compositions in the Ca alpha-SiAlON ( alpha') system has been fabricated using pressureless sintering to eva luate the phase relationships on, and near, the Ca alpha' plane. A pha se behavioral diagram for the Ca alpha' plane within the Janecke prism has been determined and found to be similar to those for the Y and Sm alpha' systems. However, distinct differences were also observed; two additional regions (alpha' + 27R + liquid) and (alpha' + 33R + liquid ) have been identified. Investigation of the microstructures revealed elongated Ca alpha' grains in the samples prepared by pressureless sin tering. The aspect ratio of the elongated grains of alpha'increased as the concentration of stabilizing cation was increased. Single crystal line phase Ca alpha' samples of comparable density to hot-pressed mate rial were fabricated successfully using pressureless sintering.