High temperature mechanical properties of porous Si3N4 prepared via SRBSN

The high temperature strength and fracture behavior of porous Si3N4 ceramics prepared via reaction bonded Si3N4 (RBSN) and sintered reaction bonded Si3N4 (SRBSN) were investigated at 800-1400 °C. The weight gain after oxidation for 15 min and the microstructure of the edge and center of the fracture surface clearly show that the internal oxidation of porous SRBSN is unavoidable with porosity of ~ 50% and mean pore size of 700 nm. The oxidation of Si3N4 and intergranular Y2Si3O3N4 phase may responsible for the high temperature strength degradation of SRBSN. Porous Si3N4 ceramics prepared with addition of 1 wt% C showed low strength degradation at temperature > 1200 °C.