Effect of amount and composition of additives on the fracture toughness of silicon nitride (original) (raw)

All specimens with 4-16 vol% of additives and the molar ratio of 2-5 showed sintered densities higher than 99.6% of theoretical density. Phase analysis of the samples by X-ray diffraction (XRD) showed fl-Si3N4, Si2N20 and Y2Si207. Typical microstructure morphology and grain size of specimens were similar, as shown in Fig. 1. Fig. 2 shows the fracture toughness of Si3N4 as a function of the amount of additives. The lower fracture toughness was obtained for the specimen with 4vo1% of additives and higher fracture toughness was obtained for the specimens with 8-16vo1% of additives. It is consistent with the microstructural observations shown in Fig. 1, where a less tortuous crack path was observed for the specimen with 4 vol % of additives as compared with the specimens with 12 vol% of additives. However, for the specimens with 8-16vo1% of additives, fracture toughness was insensitive to the amount of additives. This may be due to the same property of grain boundary glassy phases irres...