FeCrMg composite and porous FeCr obtained by dealloying in metallic melt bath by Xray tomography and SEM

Abstract

Nanoporous metals have attracted considerable attention for their excellent functional properties [Snyder, 2010]. The most promising technique used to prepare such nanoporous metals is dealloying in aqueous solution. Nanoporous noble metals including Au have been prepared from binary alloy precursors [Forty, 1979]. The less noble metals, unstable in aqueous solution, are oxidized immediately when they contact water at a given potential so this process is only possible for noble metals. Porous structures with less noble metals such as Ti or Fe are highly desired for various applications including energy‐harvesting devices [Sivula, 2010]. To overcome this limitation, a new dealloying method using a metallic melt instead of aqueous solution was developed [Wada, 2011]. Dealloying in the metallic melt is a selective dissolution phenomenon of a mono‐phase alloy solid precursor: one component (referred as soluble component) being soluble in the metallic melt while the other (referred as targeted component) is not. When the solid precursor contacts the metallic melt, only atoms of the soluble component dissolve into the melt inducing a spontaneously organized bi‐continuous structure (targeted+sacrificial phases), at a microstructure level. This sacrificial phase can finally be removed by chemical etching to obtain the final nanoporous materials. Because this is a water‐free process, it has enabled the preparation of nanoporous structures in less noble metals such as Ti , Si , Fe , Nb, Co and Cr . In this study, nanoporous FeCr samples were prepared using Ni as the soluble component, in a metallic melt bath of Mg . To introduce structural and mechanical anisotropy, some samples were cold‐rolled before etching. The influence on the microstructure of the precursor composition, the dealloying conditions and the rolling process were investigated along the different steps by SEM‐EBSD and Xray tomography to correlate the process with the microsctructure. Xray tomography (cf. Fig. 2 and 4)enables us to characterize qualitatively and quantitatively the volume while SEM (cf. Fig. 1 and 3) enables us to analyze larger areas with higher resolution 2D images. To confirm the validity of Xray tomography results, SEM‐FIB analysis were also performed.