Abstract
The influence of sintering parameters at an early stage of densification on the evolution of a bimodal microstructure in Si 3N 4 ceramics was investigated. Commonly two different methods are pursued to design a bimodal Si 3N 4 microstructure: (i) annealing at a later sintering stage ( T > 1850 °C) initiating β-Si 3N 4 grain growth via Ostwald ripening and (ii) seeding with β-Si 3N 4 nuclei, which abnormally grow during the liquid-phase sintering process. In this study, a third and novel method to design Si 3N 4 microstructures by affecting intrinsic nucleation phenomena at an early sintering stage is presented. In order to study the influence of sintering parameters on β-Si 3N 4 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-Si 3N 4 nucleation. This procedure allows variation in the fineness of the matrix as well as in the number and dimension of the large elongated β-Si 3N 4 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.
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