Variation of sintering parameters at an early stage of densification affecting β-Si3N4-microstructure

The influence of sintering parameters at an early stage of densification on the evolution of a bimodal microstructure in Si3N4 ceramics was investigated. Commonly two different methods are pursued to design a bimodal Si3N4 microstructure: (i) annealing at a later sintering stage (T > 1850 °C) initiating β-Si3N4 grain growth via Ostwald ripening and (ii) seeding with β-Si3N4 nuclei, which abnormally grow during the liquid-phase sintering process. In this study, a third and novel method to design Si3N4 microstructures by affecting intrinsic nucleation phenomena at an early sintering stage is presented. In order to study the influence of sintering parameters on β-Si3N4 nuclei formation during the early stage of densification, temperature and pressure were systematically changed. Starting from identical green bodies (identical processing and doping), the variation of the sintering parameters affected intrinsic β-Si3N4 nucleation. This procedure allows variation in the fineness of the matrix as well as in the number and dimension of the large elongated β-Si3N4 grains embedded in the matrix. Since identical green bodies are used as starting material, the resulting microstructure can easily be tailored toward corresponding application needs.