Fabrication and mechanical characterization of nanoporous ceramic composites for potential toughening

Ceramic materials are essential for aerospace and other applications involving extreme environment, due to their unique combination of properties including low density, high strength, thermal stability and corrosion resistance. However, their applications are currently limited as a result of ceramics’ intrinsic brittleness originated from ionic and covalent bonding. While ceramics are traditionally toughened through flaw size and distribution reduction, fiber/whisker reinforcement, crack deflection etc., novel toughening strategy by introducing nanoporosity has been demonstrated to increase ceramics ability to deform in a quasi-ductile manner, potentially leading to enhancement in fracture toughness. In this study, first, the effect of nanoporosity on mechanical properties and deformation behavior of ceramic materials is parametrically studied through nanoindentation on anodic aluminum oxide (AAO) membranes, which possess well-organized nanoporous microstructure. Novel deformation mechanisms such as formation of shear bands in the form of arrays of collapsed nanopores were identified and exhibit transition with respect to influencing parameters such as phase, interpore distance/pore size and porosity. Second, scalable manufacturing of nano-porous boron carbide composites is being attempted using field assisted sintering technology (FAST) to yield tunable nanoporous structure. Compared to traditional sintering methods such as hot-pressing, FAST exhibit multiple benefits including shorter sintering time, lower sintering temperature and more uniform heating process which can yield finer grains and better control over the microstructure of sintered samples. In this paper, a brief introduction of FAST and intended manufacturing process will be given, followed by demonstration of preliminary results from sintering of boron carbide and its composites.