Fabrication, mechanical properties and microstructure analysis of Si3N4/SiC nanocomposite

Ceramic nanocomposites, Si3N4 matrix reinforced with nano-sized SiC particl es, were fabricated by hot pressing the mixture of Si3N4 and SiC fine powde rs with different sintering additives. Distinguishable increase in fracture strength at low and high temperatures was obtained by adding nano-sized Si C particles in Si3N4 with Al2O3 and/or Y2O3. Si3N4/SiC nanocomposite added with Al2O3 and Y2O3 demonstrated the maximum strength of 1.9 GPa with avera ge strength of 1.7 GPa. Fracture strength of room temperature was retained up to 1400 as 1 Cpa in the sample with addition of 30 nm SiC and 4 wt% Y2O3 . Striking observation in this nanocomposite is that SiC particles at grain boundary are directly bonded to Si3N4 grain without glassy phases. Thus, s ignificant improvement in high temperature strength in this nanocomposite c an be attributed to inhibition of grain boundary sliding and cavity formati on primarily by intergranular SiC particles, besides crystallization of gra in boundary phase. (C) 1999 Elsevier Science Ltd. All rights reserved.