Influence of the grain-boundary phase amount on properties of dense Si3N4

By means of model experiments, the influence of the grain-boundary phase amount in dense silicon nitride on properties at room and high temperatures (up to 1400 degrees C) was evaluated. In this respect, the concentration of sintering additives was lowered from 6 mass-% to 4 mass-% and finally only 2 mass-% Y2O3, by simultaneously keeping the Y2O3/SiO2-ratio constant. Additionally, different silicon nitride powders were used with constant Y2O3-addition to determine the influence of the powder purity. Consolidation occurred by hot-pressing in order to provide nearly identical thermal history of the samples.