Preparation of graded silicon nitride ceramics with high mechanical performance using β-Si3N4 seeds

In this study, the graded silicon nitride ceramics were prepared by hot-pressing method combined with beta-Si3N4 seeds. The composites with alpha-Si3N4 rich content were applied in the outer layers while the composites with elongated beta-Si3N4 rich content were applied in the inner layers. Their mechanical properties and cutting performance of graded silicon nitride ceramics were evaluated in detail. The experimental results show that not only the level of hardness and cutting performance of silicon nitride ceramics can remain high, but also their flexural strength and fracture toughness can be significantly improved. Furthermore, the obtained graded silicon nitride ceramics were of a homogenous composition, and the interface between outer and inner layer was well bonded and free of defects such as cracks, pores, and agglomerates. These results indicate that this proposed method is a very promising and simple approach for the preparation of high mechanical performance of silicon nitride ceramics.