Properties of Hot Compressed 21R SiAlON Ceramics with a Samarium Oxide Additive.

The compaction of initial powders, the bending strength, and the microhardness of 21R sialon ceramics obtained by hot pressing have been studied experimentally. It is found that the Sm₂O₃ sintering additive substantially reduces the annealing temperature and enhances the properties of the ceramics. The samples of 21R sialon ceramics without additives, which are prepared by annealing at 1950°C, have a density of 3.01 g/cm³, a bending strength of 240 ± 15 MPa, and a Vickers microhardness of 16.2 ± 0.4 GPa; the samples of 21R sialon ceramics with 2.5 wt % Sm₂O₃, which are annealed at 1750°C, are characterized by a density of 3.39 g/cm³, a bending strength of 315 ± 16 MPa, and a Vickers microhardness of 21.9 ± 0.2 GPa. It is shown that Sm₂O₃ reacts with 21R sialon in the temperature range of 1600–1700°C to form the 27R sialon and SmAlO₃ impurity phases. In the samples annealed at 1750°C, the 27R sialon and Sm–sialon (Sm₃Si_2.5Al_3.5O_12.5N_1.5) impurity phases are detected. [ABSTRACT FROM AUTHOR]