Densification of Si3N4/Si3N4-fibre composites

Mixtures of commercial alpha-Si3N4 powders, and oxide additives, with beta-Si3N4 monocrystalline fibers or beta-S3N4 prismatic grains have been prepared. The influence of the oxide additives on the transformation alpha --> beta, densification rate and microstructure have been analyzed. The addition of beta-Si3N4, in the form of fibers as well as grains, promoted transformation but retarded densification. This decrease in sintering rate has been overcome by increasing the amount of additives. The addition of beta-Si3N4 produced a coarsening of the microstructure of these materials, being it more pronounced in the case of the fiber composite.