EFFECTS OF MATRIX GRAIN-SIZE ON THE MECHANICAL-PROPERTIES OF SI3N(4) SIC NANOCOMPOSITES DENSIFIED WITH Y2O3/

Effects of matrix grain size on the room-temperature mechanical proper ties and high-temperature creep behavior were investigated for Si3N4/3 0 vol% SiC nanocomposites. The nanocomposites with different matrix gr ain sizes were fabricated by hot-pressing the mixtures of nano-sized b eta-SiC (40 nm) and alpha-Si3N4 (200 nm) powders. 8 wt% of Y2O3 was us ed as an sintering aid. With increasing the hot pressing time, the alp ha-beta transformation and grain growth of rod-like beta-Si3N4 were pr omoted and the number of equiaxed grains decreased. The fracture stren gth and toughness were improved and the creep rate at 1400 degrees C a nd 200 MPa decreased. The observed improvement of mechanical propertie s and creep resistance was rationalized by the microstructural changes .