Abstract
Abalone nacre is a natural ceramic-based composite consists of 95 wt% stacked CaCO3 tiles and 5 wt% organic layers organized into a unique multilayer structure, which leads to exceptional fracture toughness. The major toughening mechanism is the crack deflection at the organic/inorganic interfaces so that the crack cannot propagate through the shell directly. Furthermore, interfacial roughness and interconnected mineral bridges between tiles can further prevent plastic deformation. Inspired from abalone nacre, multilayer films of zirconia and polyimide layers are synthesized by the hybrid PVD system combining sputtering and pulsed laser deposition. Zirconia is an intrinsically tough ceramic material. By introducing the polyimide interlayer, the fracture toughness of multilayer films can be significantly enhanced, six times higher than that of zirconia monolayer. The thickness ratio of zirconia and polyimide is kept 10:1, and the period thickness is altered to investigate effect the interfaces on the mechanical properties. Results show that multilayer structure can enhance the fracture toughness of thin film: fracture toughness increases with increasing number of interlayers yet the hardness decreases. SEM observation verifies that the major toughening mechanism of bio-inspired multilayer films is crack deflection at organic/inorganic interfaces, which prevent crack from direct propagation. The interfacial roughness can also enhance mechanical properties in certain situations and the mechanisms are discussed.