Nondestructive Evaluation of Surface Properties of Sintered Si3N4 Ceramics with Surface Wave Dispersion

Elastic properties of high-performance ceramics is usually measured with ultrasonic bulk waves [1]. However, the bulk waves gives us only properties averaged over sample thickness. Sintered ceramics often have properties at the surface different from in the middle. Thus we need a method which distinguishes near surface property from the averaged one. Surface wave technique has been applied for nondestructive characterization of ceramics [2–4]. The depth-dependent properties of ceramics, however, has never been reported. Surface wave propagates in subsurface layer of about one wavelength. Therefore we’ll be able to estimate the depth-dependent properties of the ceramics, if we’ll use surface waves of different frequency or wavelength