On factors defining the mechanical behavior of nanoporous gold

Nanoporous gold (NPG) made by dealloying takes the form of a network of nanoscale struts or ligaments. It is well established that the material's mechanical behavior is strongly affected by its ligament size, L and by its solid volume fraction, phi. We explore the mechanical behavior of NPG, with an emphasis on establishing a consistent data set with comparable L but covering a significant range of initial phi. Specimens are prepared from Ag-Au master alloys with their Au atom fraction, x(Au)(0) in the range 0.20-0.35. Since dealloying replaces Ag with voids, phi may be expected to agree with x(Au)(0). Yet, spontaneous plastic deformation events during dealloying can result in macroscopic shrinkage, decoupling phi from x(Au)(0). This raises the question, how do phi and x(Au)(0) separately affect the mechanical behavior? We confirm two recent suggestions, namely i) a modified Roberts-Garboczi-type scaling law for Young's modulus versus phi of the material in its as-prepared state and ii) the relevance of an apparent load-bearing solid fraction for Young's modulus as well as strength. Yet, remarkably, we find that stiffness and strength of the as-prepared material show a much better correlation to x(Au)(0) as compared to phi. This can be understood as a consequence of the microstructural changes induced by shrinkage. Studying the microstructure evolution during annealing, we also confirm the suggestion that coarsening entails an enhanced loss in stiffness for samples with lesser solid fraction. This finding confirms concerns about the notion of self-similar coarsening as a general behavior of dealloying-made network materials. (C) 2021 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Automated summary

Nanoporous gold (NPG) made by dealloying exhibits mechanical behavior strongly influenced by ligament size and solid volume fraction. Stiffness and strength of the material show a better correlation to the gold atom fraction x(Au)(0) compared to the solid volume fraction phi. Spontaneous plastic deformation events during dealloying may lead to macroscopic shrinkage, decoupling phi from x(Au)(0).