Preparation of β-Si3N4 seeds and self-reinforced Si3N4 ceramics

Firstly, rod-like beta-Si(3)N(4)crystal particles were prepared by the heating of alpha-Si3N4 powder with Yb2O3 and MgO at 1 700degreesC and 1 650degreesC, respectively. Then self-reinforced silicon nitride ceramics were obtained by HP-sintering of alpha-Si3N4 powder, Yb2O3 and the as-prepared seeds. The results indicate that the beta-Si3N4 crystal particles, which are favored for use as the seed, can be obtained when the Yb2O3 and MgO are used as the additive. The introduction of two kinds of the seed can improve the fracture toughness of the materials. However, the residual phase in the seeds strongly affects on the high-temperature strength. TEM characterization shows that the presence of the Mg-containing phase is an important cause of a decrease in high-temperature strength and of the crystallization of intergranular phase.