Interface Failure in Nacre-like Alumina
Among many bioinspired materials contenders, ceramic-ceramic composites based on alumina platelets have recently emerged as a new class of strong and damage-resistant materials. These materials are brick-and-mortar composites, where bricks are single-crystal alumina platelets, and a glassy interphase acts as the mortar. Although several processing approaches have been reported to date, these materials were optimized so far by trial-and-error approaches. Understanding the fracture properties of nacre-like alumina requires the knowledge of the properties of each of its components. However, only the properties of alumina platelets have been evaluated so far. Here we characterize at a micro scale the fracture property of an aluminosilicate glass interphase between alumina platelets. Micro-cantilever specimens prepared by FIB milling are tested under bending in order to characterize the failure of interfaces exhibiting orientations between 0° and 90° with respect to the beam direction, and thus undergoing different combined shear and tensile stress. Failure appears to be mainly driven by the interface opening stress that seems to predominate over shear stress. The apparent fracture stresses vary from 0.5 GPa to 3.0 GPa depending on the interface angle. It results in a maximum opening stress of 0.72 ± 0.18 GPa reached locally at the interface, whereas the apparent tensile fracture stress of a pack of aligned and perpendicular platelets is approximately 3 GPa. These results should help understand the bulk properties of nacre-like alumina composites and future similar materials and enable a rational design of their components and microstructures.