EFFECTS OF BALL-MILLING TIME ON THE PROPE RTIES OF LAW PURITY BETA-PHASE SILICON-NITRIDE POWDER AND THE HOT-PRESSED BODY

Y2O3-doped low purity beta-Si3N4 powder was ball-milled for 6 to 100h. The effects of ball-milling time on the properties of the powder and the hot-pressed body were investigated. As increasing ball-milling tim e, average particle size and crystallite size decreased and the amount of SiO2, carbon, some metallic impurities and lattice strain increase d for the ball-milled powder. The increase of SiO2 was ascribed to the mechanochemical reaction of H2O contained in the milling fluid with n ewly formed powder surfaces. The source of carbon was both the milling fluid and the container. The increase of Al and Mg was explained by t he wear of milling balls. Sintering behavior and microstructure of the sintered bodies were influenced by the powder properties modified by different ball-milling time. Mechanical properties were strongly depen dent on their microstructures.