Copper Surfaces with Bimodal Nanoporosity by Microstructural Length Scale Controlled Dealloying of a Hypereutectic Al-Cu Alloy

Copper (Cu) surfaces with bimodal nanoporosity can be used for a variety of applications. This research shows that bimodal nanoporous Cu surfaces can be fabricated by dealloying of an as-cast hypereutectic alloy Al75Cu25 (at.%) alloy, which solidifies as pre-eutectic Al2Cu (micrometre-scaled) and eutectic lamella of α-Al/Al2Cu (nanoscaled). The bimodal nanoporous Cu surface is a result of a microstructural length scale controlled dealloying process: In the beginning, the micrometre-scaled Al2Cu acts as a cathode enabling the preferential dissolution of α-Al (anode) for larger pores to form. Afterwards, the nanosize effect of α-Al overrides the intrinsic difference in electrochemical potential allowing for subsequent simultaneous dealloying leading to finer pores. The assessment of the in situ Synchrotron XRD data of the formation of bimodal nanoporous Cu surfaces revealed a two-stage kinetic process, closely related to the formation of bimodal pores during the microstructural length scale controlled dealloying process. The underlying rationales and implications are discussed.