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 (α′) system has been fabricated using pressureless sintering to evaluate the phase relationships on, and near, the Ca α′ plane. A phase behavioral diagram for the Ca α′ plane within the Jänecke prism has been determined and found to be similar to those for the Y and Sm α′ systems. However, distinct differences were also observed; two additional regions (α′+ 27R + liquid) and (α′+ 33R + liquid) have been identified. Investigation of the microstructures revealed elongated Ca α′ grains in the samples prepared by pressureless sintering. The aspect ratio of the elongated grains of α′ increased as the concentration of stabilizing cation was increased. Single crystalline phase Ca α′ samples of comparable density to hot‐pressed material were fabricated successfully using pressureless sintering.