Microstructural Changes in Beta-silicon Nitride Grains Upon Crystallizing the Grain-boundary Glass

Crystallizing the grain-boundary glass of a liquid-phase-sintered Si3N4 ceramic for 2 h or less at 1500° led to formation of δ-Y2Si2O7. after 5 h at 1500°, the δ-Y2Si2O7 had transformed to β-Y2Si2O7 with a concurrent dramatic increase in dislocation density within β-Si3N4 grains. Reasons for the increased dislocation density are discussed. Annealing for 20 h at 1500° reduced dislocation densities to the levels found in as-sintered material.