Dealloying-induced phase transformation in Fe-Rh alloys

Nanoporous metals produced by dealloying have aroused enormous interest due to exotic mechanical and physico-chemical properties that are usually inaccessible in their bulk form. Interestingly, when binary solid-solution alloys, such as Ag-Au alloys, are dealloyed, the resulting nanoporous metals usually inherit the crystal structure of their parent alloys. In this Letter, we examined the evolution of the crystal structure during the dealloying of Fe-Rh alloys that show single-phase solubility over a large range of compositions. In situ x-ray diffraction shows that the crystallographic structure of the Fe85Rh15 alloy transforms from the original bcc to fcc structure during the dealloying. Transmission electron microscopy confirms the fcc structure of the nanoporous sample, which exhibits a typical bi-continuous porous structure with ligament sizes of only 2-3 nm and a high Fe concentration. The bcc-fcc transformation is driven by the chemical disordering of Fe and Rh atoms, induced by the highly dynamic dissolution and diffusion process at the alloy/electrolyte interface. Our study highlights the massive diffusion and the consequent disordered arrangement of elemental components during the evolution of the nanoporous structure.