Effect of the Whisker Content on the Microstructure and Properties of Silicon Nitride with Aligned Whisker Seeds

Abstract

Silicon nitride ceramics with different amounts of aligned reinforcing grains were prepared using 3 wt%, 5 wt% and 7 wt% β-Si₃N₄ whiskers. The degree of alignment of the reinforcing grains was increased as the whisker content was increased as determined by the linear sintering shrinkage anisotropy. The number of the aligned reinforcing grains was increased as the whisker content was increased, but volume fraction occupied by those grains was the maximum for silicon nitride with 5 wt% β-Si₃N₄ whiskers. The fracture toughness and the flexural strengths at room temperature were increased as the whisker content was increased while the flexural strength at 1673 K was the maximum for silicon nitride with 5 wt% β-Si₃N₄ whiskers. Those properties were closely related to the microstructures of the silicon nitride ceramics.