Acoustic Microscopy of Ceramic Surfaces

Mechanical properties of ceramic surfaces such as hardness, indentation fracture toughness, and wear resistance are largely influenced by the behavior of small flaws and defects, such as microcracks, delaminations, voids, and inclusion located beneath the surface. Acoustic microscopy is particularly suited to study this phenomenon because it can image microscopic subsurface features without sectioning. Furthermore, it has been revealed that the velocity and attenuation of the leaky surface wave can be measured; these are expected to have close correlation with the mechanical properties of materials. New results on the nondestructive observation of subsurface cracks of Si3N4 and ZrO2 and delamination of TiN coatings introduced by Vickers indentation or sliding contacts are presented. The mechanism of delamination and wear of these materials is discussed. It is shown that the velocity and attenuation of the leaky surface wave of TiN coatings and sintered Al2O3 actually have close correlation with the hardness and wear resistance of these materials. The reason for these correlations is also discussed.