SHOCK-YIELDING PROPERTIES OF SI3N4 CERAMICS - CORRELATION WITH THE MICROSTRUCTURE AND STATIC MECHANICAL STRENGTH

Hugoniot-compression curves for Si3N4 ceramics with controlled microstructure were measured to study the yielding properties under shock compression, and the correlation with the microstructural characterization and the static mechanical strength. Hugoniot-measurement experiments were performed on 4 kinds Of Si3N4 ceramics by means of the inclined-mirror method combined with a powder gun. The Hugoniot-elastic limits of fine-grained Si3N4 ceramics and the SiC whisker-reinforced Si3N4 ceramics (within 14-20 GPa) were greater than the conventional Si3N4 (10-12.5 GPa). It was found that the strength Of Si3N4 ceramics under shock compression is strongly influenced by their microstructure, and the key to the high Hugoniot-elastic limit is to achieve a fine-grained microstructure or a composite structure containing high-strength materials such as SiC whiskers. It was also pointed out that the yield strength per unit weight under shock compression of the Si3N4 monolithic ceramics was proportinal to the static strength, but the yield strength per unit weight under shock compression of the SiC whisker reinforced Si3N4 was comparatively larger than that of monolithic Si3N4. In addition, it was suggested that the Hugoniot-measurement experiments are useful for evaluating the performance of ceramics, because the ceramics show the strength close to the intrinsic value under shock compression, due to the very high strain rate at the shock wave front.