Nonbrittle nanopore deformation of anodic aluminum oxide membranes

Quasi-ductile deformation of nanopores was studied by conducting nanoindentation tests on a consistent sample set of anodic aluminum oxide (AAO) membranes with varying porosity, interpore distances, and phases. The small feature size (wall thickness) of the nanoporous structure was identified as the key parameter to trigger and enhance nonbrittle, quasi-ductile nanopore deformations, regardless of material phase. With small wall thickness (<~100 nm), shear-banding-like and foam-like compressed nanopores were observed with amorphous AAO samples due to increased open space within long-range disordered atomic arrangement, while shear-banding-like arrays of collapsed nanopores were observed with polycrystalline AAO samples due to grain boundary sliding and nanocrack formation. The above obtained knowledge can be a useful reference for the future design and applications of nanoporous ceramics with enhanced ductility, and thus fracture toughness, but without sacrificing stiffness, hardness, and strength. Future work includes scalable manufacturing of nanoporous structures with tunable pores (porosity, size, and distribution), grains, and interfaces using field assisted sintering technology (FAST), and their multi-scale structure-property relationship study.