Microstructural characterization of GPSed-RBSN and GPSed-Si3N4 ceramics

Microstructural characterization of gas-pressure-sintered reaction-bonded S i3N4 (GPSed RBSN) and gas pressure-sintered Si3N4 (GPSed Si3N4) ceramics at 2223 K far 12.6 ks has been investigated using by back-scattered SEM, TEM and XRD. No residual Si phase was observed in reaction bonded body nitrided at 1673 K for 72 ks, but many residual pores with about 3 mu m was observe d. Most of Si3N4 grain boundaries and triple points in both GPSed bodies we re covered with amorphous phases. The aspect ratio of large rod-like Si3N4 grains in GPSed Si3N4 was about 10, which was larger than that in GPSed RBS N body. The main fracture mode in both sintered bodies was intergranular fr acture with rough surfaces. The values of fracture toughness and fracture s trength in both samples were 7.8 MPa.m(1/2), 731 MPa and. 8.0 MPa.m(1/2). 6 32 MPa, respectively.