Tailoring the Microstructure of Duplex Si_3N_4-Based Ceramics by Pre- and Post-Sintering Heat-Treatment

摘要

The possibility of tailoring the microstructure of Y- and rare-earth- (R) doped Si_3N_4 based ceramics will be discussed in some detail. Attention will be focused on the effect of sintering time and temperature 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 Si_3N_4 corner in the Ce-Si-Al-O-N system have been prepared by hot-pressing at 1800 ℃. A sintering time of 15 min yielded a material which consisted of sub-micron sized α- Si_3N_4 particles and a small number of elongated |3-sialon grAlNs embedded in a glassy phase. Prolonged sintering time (2 hours) yielded a compact contAlNing the β-sialon and JEM phases but no α-Si_3N_4 particles. Nd-doped sialon ceramics with an overall composition close to the α-β-sialon boundary were prepared by hot-pressing for 2 and 24 hours at 1800 ℃. The microstructure obtAlNed after 24 hours' hot-pressing could be mimicked by 100 hours' post heat treatment at 1650 ℃ of the sample hot pressed for 2 hours at 1800 ℃ . 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 ℃.