Anisotropy detection in hot-pressed silicon nitride by acoustic microscopy using the line-focus beam

Anisotropy in velocity and attenuation of leaky surface-acoustic waves (leaky SAWs) on hot-pressed silicon nitride was measured by acoustic microscopy using the line-focus beam. On the surface normal to the pressing direction the velocity was 5651 m/s for all propagation directions, whereas on the surface parallel to the pressing direction the velocities varied markedly, depending on the wave propagation direction¿typically 5726 m/s along the direction normal to the pressing axis and 5642 m/s along the direction parallel to the pressing axis. Because the fracture toughness KIC, measured by the Vickers indentation technique, also showed an anisotropy on the surface normal to the pressing direction, the anisotropic velocity measurement of the leaky SAWs proved to be useful in the NDE of anisotropic mechanical properties of ceramics products made by hot-pressing.