In situ synthesis of Si3N4/h-BN composites by hot-pressed sintering

Various methods have been implemented to deal with the problem of the aggregation of h-BN in the Si3N4 matrix, thereby improving the machinability of Si3N4 ceramics. In this paper, the in-situ phase transformation of c-BN was introduced to prepare hot-pressed Si3N4/h-BN composites. Results show that compared with the direct addition of h-BN, the h-BN generated by the phase transformation of c-BN was more homogeneously disperse in Si3N4 matrix. Meanwhile, the phase transition (c -> h-BN) enhanced the densification process, and the retarding effect of BN on the alpha ->beta-Si3N4 phase transformation and the Si3N4 grain growth was weakened. Thereby, the interlocking microstructure of elongated grains was greatly improved, and the fracture toughness and flexural strength of Si3N4/h-BN composites increased by 9.2 % and 11.5 %, respectively, after the addition of 5 vol% cBN. The proposed method provides a new idea for the preparation of composite ceramics.