Intrinsic Toughness/Brittleness of Nanoporous Ag: Depending on Network Connectivity and Micro-Cracks

The effective engineering applications of nanoporous metals (NPMs) require uniform ligaments network, specifically crack-free and ductile monolithic bodies. Here we investigate the effects of ligament-network connectivity and micro-cracks on the mechanical properties of nanoporous Ag (np Ag). The well-interconnected np Ag metal exhibits higher tensile strength, nanohardness and Vickers hardness than those for the ill-interconnected np Ag metal. The quality of the network connectivity dominates the strength and hardness of the np Ag. The ductility/brittleness is determined by the micro-crack in np Ag. The crack-free np Ag exhibits good ductile behavior. When micro-cracks are introduced, the np Ag becomes brittle. The np Ag with many micro-cracks is easily crushed because the cracks nucleate from the inherent micro-cracks and quickly propagate along the concentrated stress. The low values of volume shrinkage rate (V_sr) and surface diffusivity (D_s) effectively suppress the crack initiation and propagation of as-formed np Ag. These results provide useful insights to synthesize more flexible and crack-free NPM materials for effective use in diverse engineering applications.