Characterization of Subsurface Damage Zone in SiC and Si3N4 Ceramics with Static and Dynamic Indentation

Abstract

Silicon carbide (SiC) and Silicon nitride (Si3N4) are the most successful engineering ceramics, owing to a favorable combination of properties, including high strength, hardness, and freacture toughness and low thermal expansion coefficient. However, the impact damage behavior of SiC and Si3N4 ceramics has not been widely characterized. In this work, ‘static’ sphere indentation and ‘dynamic’ explosive indentation were conducted to characterize the impact damage behavior of SiC and Si3N4 ceramics with various microstructures and sintering additives. In SiC, the effect of rare-earth oxides, the typical sintering additives, on subsurface damage upon static and dynamic indentation was studied. In Si3N4, 3 grades with different grain size and shapes (fine-equiaxed, medium and coarse-elongated) were prepared. In order to observe the subsurface damage zone, a bonded-interface technique was adopted. Subsurface evolution of the specimen was then characterized extensively using optical microscopy, SEM, and TEM. In case of static indentation, examination of subsurface damage reveals the competition between brittle and ductile damage modes. Dynamic indentation, however, induces a massive subsurface yield zone that contains extensive micro-faults. It is suggested that the grain boundary phase plays an important role in dynamic fracture as well as in static fracture behavior of ceramics.