The Research on High Pressure Sintering of Mixed Powder γ-Si3N4 and α-Si3N4

The high pressure and high temperature sintering of alpha-Si3N4 and gamma-Si3N4 with Y2O3-Al2O3-La2O3 as additives were studied under pressures of 5.4 GPa and temperatures of 1420-1770 K. The effects of sintering temperatures and pressures on properties of sintered ceramic samples were investigated with X-ray diffraction and scanning electron microscopy. The results show that gamma-Si3N4 and alpha-Si3N4 is transformed to beta-Si3N4 completely. The highest relative densities and Vickers hardness (H-V) of sintered samples are 98.71 and 21.76GPa, respectively. The sintered samples were composed of elongated beta-Si3N4 rod crystals with disordered orientation and had intergranular interlocks and uniform and compact microstructure. Pulled out crystal grains on the fractured cross sections were obviously observed by SEM.