Fracture energies of tape-cast silicon nitride with β-Si3N4 seed addition

The fracture energies of the tape-cast silicon nitride with and without 3 wt% rod-like beta-Si3N4 seed addition were investigated by a chevron-notched-beam technique. The material was doped with Lu2O3-SiO2 as sintering additives for giving rigid grain boundaries and good heat resistance. The seeded and tape-cast silicon nitride has anisotropic microstructure, where the fibrous grains grown from seeds were preferentially aligned parallel to the casting direction. When a stress was applied parallel to the fibrous grain alignment direction, the strength measured at 1500 degrees C was 738 MPa, which was almost the same as room temperature strength 739 MPa. The fracture energy of 2 the tape-cast Si3N4 without seed addition was 109 and 454 J/m(2) at room temperature and 1500 degrees C, respectively. On the contrary, the fracture energy of the seeded and tape-cast Si3N4 was 301 and 781 J/m(2) at room temperature and 1500 degrees C, respectively, when a stress was applied parallel to the fibrous gain alignment. The large fracture energies were attributable primarily to the unidirectional alignment fibrous Si3N4 grains.