Research on Sintering Stability of Cubic Silicon Nitride Synthesized by Shock-wave

Silicon nitride ceramics was prepared by super-high pressure using theγ-Si_3N_4 powders synthesized by the shock-wave technique as raw materials and with Y_2O_3-Al_2O_3-La_2O_3 mixtures as additives at 5.7GPa from 1370K to 1670K.The stability,relative density,mechanical properties and microstructure of the compacts synthesized at different temperatures were investigated.The results show thatγ-Si_3N_4 is completely transformed toβ-Si_3N_4 at temperature from 1420K to 1670K,and partly transformed toβ-Si_3N_4 at 1370K.Micro-analysis indicates that the typical microstructure of sintered Si_3N_4 is mainly composed ofβ-Si_3N_4 rod crystals with disordered orientation and uniform microstructures.The relative density and Vickers hardness in the as-sintered (5.TGPa,1370K) samples are 98.83% and 21.09GPa,respectively.