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 Si(3)N(4) ceramics was investigated. Commonly two different methods are pursued to design a bimodal Si(3)N(4) microstructure: (i) annealing at a later sintering stage (T > 1850 degrees C) initiating beta-Si(3)N(4) grain growth via Ostwald ripening and (ii) seeding with beta-Si(3)N(4) nuclei, which abnon-nally grow during the liquid-phase sintering process. In this study, a third and novel method to design Si(3)N(4) Microstructures by affecting intrinsic nucleation phenomena at an early sintering stage is presented. In order to study the influence of sintering parameters on beta-Si(3)N(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 beta-Si(3)N(4) nucleation. This procedure allows variation in the fineness of the matrix as well as in the number and dimension of the large elongated beta-Si(3)N(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. (c) 2004 Elsevier Ltd. All rights reserved.