Fracture Energies of Tape‐Cast Silicon Nitride with β‐Si3N4 Seed Addition

Abstract

The fracture energies of the tape‐cast silicon nitride with and without 3 wt% rod‐like β‐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°C was 738 MPa, which was almost the same as room temperature strength 739 MPa. The fracture energy of the tape‐cast Si3N4 without seed addition was 109 and 454 J/m2 at room temperature and 1500°C, respectively. On the contrary, the fracture energy of the seeded and tape‐cast Si3N4 was 301 and 781 J/m2 at room temperature and 1500°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.