Anisotropy of creep deformation rate in hot-pressed Si3N4 with preferred orientation of the elongated grains

Compressive creep deformation of hot-pressed silicon nitride with two different preorientations of grain was investigated at temperatures in the range of 1300–1400 °C under 30–100 MPa. The stress exponent of the creep rate was determined to be nearly unity of the apparent activation energy of creep rate was found to be about 500 kJ mol^-1. It means the creep deformation is due to diffusion controlled solution/precipitation. Creep rate of specimen with creep loading direction in parallel to the hot-pressing axis was determined to be higher than that in perpendicular to the hot-pressing axis. In addition, microstructural observation revealed that no cavity appeared and grain boundary glass was recrystallized during creep. X-ray diffraction (XRD) analysis confirms that needle-like Si₃N₄ grains were reoriented during creep test. These results indicate that the anisotropy of creep rate results from the disparity in the rate of solution–reprecipitation of grains rather than that in diffusion through the grain boundary, which is dependent on the preferred orientation of the needle-like grains. This revised version was published online in November 2006 with corrections to the Cover Date.