Microscopic failure behavior of nanoporous gold

We report on the fracture behavior of nanoporous (np)-Au with an open sponge-like morphology of interconnecting ligaments on the nanometer length scale. Despite its macroscopic brittleness, np-Au is microscopically a very ductile material as ligaments strained by as much as 200% can be observed in the vicinity of crack tips. Cell-size effects on the microscopic failure mechanism were studied by annealing treatments that increased the typical pore size/ligament diameter from similar to 100 nm to similar to 1 mu m. Ligaments with diameter of similar to 100 nm fail by plastic flow and necking, whereas failure by slip was observed for larger ligaments with a diameter of similar to 1 mu m. The absence of slip marks in 100-nm-sized ligaments suggests a strongly suppressed dislocation activity, consistent with the high yield strength of np-Au.