Correlation between structure and properties of Si{sub}3N{sub}4 materials with Y{sub}2O{sub}3/Al{sub}2O{sub}3 sintering additives

摘要

The chemical composition of the grain boundary phase and the concentration of Al{sup}3+ ions dissolved in the Si{sub}3N{sub}4 grains were determined by analytical transmission electron microscopy for gas-pressure-sintered I Si{sub}3N{sub}4materials with different ratios of the sintering additives Y{sub}2O{sub} 3 and Al{sub}2O{sub}3. The concentration of Al dissolved in the Si{sub}3N{sub}4 grains, i.e. the substitution parameter z, increases with increasing amount ofAl{sub}2O{sub}3 in thestarting powder. The liquid phase is enriched by Y, Si, and N as gas pressure sintering progresses. For z in the range 0,32 < z < 0,35, a maximum of bending strength, which was more pronounced at a testing temperature of 1000℃, was achieved. Thematerials with a high strength level at room and at higher temperatures (up to 1000℃) are characterised by a higher substitution parameter z, finer grains, lower thermal expansion coefficients and smaller differences in thermal strain between theamorphous grain boundary phase and the Si{sub}3N{sub}4 matrix.