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

Ceramic nanocomposites, Si3N4 matrix reinforced with nano-sized SiC particles, were fabricated by hot pressing the mixture of Si3N4 and SiC fine powders with different sintering additives. Distinguishable increase in fracture strength at low and high temperatures was obtained by adding nano-sized SiC 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 average 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, significant improvement in high temperature strength in this nanocomposite can be attributed to inhibition of grain boundary sliding and cavity formation primarily by intergranular SiC particles, besides crystallization of grain boundary phase. (C) 1999 Elsevier Science Ltd. All rights reserved.