Preparation and sintering microstructure of nanometer Fe coated Si₃N₄ composite powders

Fe/Si₃N₄ composite powder was synthesized by the heterogeneous precipitation-thermal reduction process，and then pressed into flakes under a pressure of 10 MPa. The flakes were sintered by pressureless and hot-pressing at 1873K in 0.1 MPaN₂. The chemical composition，microstructure and phases of the composite powder and the sintered flakes were investigated by scanning electron microscopy (SEM)，transmission electron microscopy (TEM)，energy dispersive  spectroscopy (EDS) and X-ray diffraction (XRD). It is proved that the structure of the composite powders is Si₃N₄ coated by nano Fe. The crystal phases of sintered flakes by pressureless are iron silicide，SiC andSi₃N₄. The crystal phases of the sintered samples by hot-pressing are Fe，iron silicide and Si₃N₄. It is found that the crystal phases flakes by pressureless and hot-pressing are very different.