The mechanical response of core-shell structures for nanoporous metallic materials

Abstract

Nanoporous gold (NP-Au) exhibits microscale plasticity, but macroscopically fails in a relatively brittle manner. This current study suggests that a core-shell structure can increase both ductility and strength of NP-Au. A core Au foam structure was created using conventional dealloying methods with average ligament size of 60 nm. Nickel was then electroplated on to the NP-Au with layer thicknesses ranging from 2.5 nm to 25 nm. Nanoindentation demonstrated a significant increase in the hardness of the coated Np-Au, to about five times of that of the pure Np-Au, and a decrease in creep by increasing the thickness of the coated Ni layer. Molecular dynamics simulations of Au–Ni ligaments show the same trend of strengthening behavior with increasing Ni thickness suggesting that the strengthening mechanisms of the Np-Au are comparable to those for fcc nano ligaments. The simulations demonstrate two different strengthening mechanisms with the increased activity of the twins in plated Au–Ni ligaments, which leads to more ductile behavior, as opposing to the monolithic Au ligaments where nucleation of dislocations govern the plasticity during loading.

Keywords:

• nanoporous gold
• de-alloying
• nanoindentation
• ductility
• strengthening mechanisms
• MD simulations

Acknowledgements

This work was supported at WSU by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences under grant no. DE-FG02-07ER46435. C. Reilly was supported by the National Science Foundation's REU program under grant no. DMR-0755055. The work at UK is based upon work supported by the National Science Foundation under grant no. DMR-0847693.