Microstructure and Mechanical Properties of Rare-Earth Doped Si3N4/SiC Nanocomposites

Influence of various rare-earth oxide sintering additives (La2O3, Y2O3, Yb2O3 and Lu2O3) on the microstructure and mechanical properties of hot-pressed Si3N4/SiC nanocomposites have been investigated. Fracture toughness of investigated materials slightly decreased with increasing ionic radius of rare-earth element (RE). Aspect ratio of the Si3N4 grains increased with decreasing ionic radius of rare-earth both in the studied Si3N4/SiC nanocomposites. Materials with higher aspect ratio of the Si3N4 grains exhibited crack deflection more frequently compared to the Si3N4 doped with lower aspect ratio, which was responsible for the higher fracture toughness. Flexural strength of the investigated materials increased with decreasing ionic radius of rare-earth elements. Significantly improved creep resistance was observed in case of nancomposite materials with smaller ionic radius of RE3+.