Thermal stability of mixed-cation α-sialon ceramics

A series of α-sialon (α′) compositions containing mixed stabilising cations were prepared, by introducing additional CaO to a basic Sm α-sialon compositions. The thermal stability of these Sm–Ca-containing α-sialon phases was investigated using XRD, SEM and EDXS techniques. It was found that the addition of calcium into the Sm α-sialon systems greatly improved the stability of the α-sialon phases. Calcium was found to be incorporated into the α-sialon structure, coexistent with the samarium, and partitioning of the calcium and samarium was observed between the α′ phase and grain boundary phases. This indicates a technique which may be used to improve the thermal stability of the α′ phase while maintaining good refractory phases at the sialon grain boundaries.