Microstructural Characterization of GPSed-RBSN and GPSed-Si3N4 Ceramics

Microstructural characterization of gas-pressure-sintered reaction-bonded Si 3 N 4 (GPSed RBSN) and gas pressure-sintered Si 3 N 4 (GPSed Si 3 N 4 ) ceramics at 2223 K for 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 μm was observed. Most of Si 3 N 4 grain boundaries and triple points in both GPSed bodies were covered with amorphous phases. The aspect ratio of large rod-like Si 3 N 4 grains in GPSed Si 3 N 4 was about 10, which was larger than that in GPSed RBSN body. The main fracture mode in both sintered bodies was intergranular fracture with rough surfaces. The values of fracture toughness and fracture strength in both samples were 7.8 MPa.m 1/2 , 731 MPa and 8.0 MPa.m 1/2 , 632 MPa, respectively.