Synthesis and mechanical properties of low crack-density bulk hierarchical nanoporous copper

Abstract

Spark plasma sintering of mixed Cu and Mn powders has been used to prepare precursor material with near-micrometer grain size for the synthesis of nanoporous copper. Dealloying of samples subsequently annealed in the Cu-Mn single-phase region results in a fully nanoporous, but extensively cracked, structure. In contrast, slow-cooling promotes the formation of copper rich-grain boundary regions as a result of grain boundary precipitation of Mn. Dealloying of this structure results in a hierarchical porous Cu with low-crack density, consisting of micro-porous grain-boundary Cu and nanoporous Cu grain-interior volumes. Samples prepared in this manner exhibit excellent mechanical properties, supporting compression to 40 % without cracking and a tensile strength of up to 60MPa. Digital image correlation shows that the grain boundary micro-porous regions promote gradual load transfer to nanoporous volumes and examination of tensile fracture surfaces reveals crack propagation both within nanoporous volumes and at the nano/micro-porous interfaces.