Tailoring the Microstructure of Duplex Si3N4-Based Ceramics by Pre- and Post-Sintering Heat-Treatment

摘要

The possibility of tailoring the microstructure of Y- and rare-earth- (R) doped Si3N4 based ceramics will be discussed in some detail. Attention will be focused on the effect of sintering time and temporature on the microstructure, but the effect of pre- and post-heat-treatment will also be discussed. Dense compacts with an overall composition close to the Si3N4` corner in the Ce-Si-Al- O-N system have been prepared by hot-pressing at 1800 deg.C. A sintering time of 15 min yielded a material which consisted of sub-micron sized a Si3N4 particles and a small number of elongated beta- sialon grains embedded in a glassy phase. Prolonged sintering time (2 hours) yielded a compact containing tbe beta-sialon and JEM phases but no aSi3N4 particles. Nd-doped sialon ceramics with an overall composition close to the alpha-beta-sialon boundary were prepared by hot-pressing for 2 and 24 hours at 1800 deg C. The microstructure obtained after 24 hours' hot-pressing could be mimicked by loo hours' post heat treatment at 1650 deg. C of the sample hot pressed for 2 hours at 180O℃ . These and more examples will show the importance of selecting the proper additives and applying an appropriate sintering procedure when designing sialon ceramics which are intended to serve at temperatures exceeding 1300 deg. C.