Kinetics and evolution of solid-state metal dealloying in thin films with multimodal analysis

Thin-film solid-state metal dealloying (thin-film SSMD) is an emerging technique that uses self -organization to design nanostructured thin films. The resulting 3D bicontinuous nanostructures are promising for a wide range of applications, such as catalysis and energy storage. In this work, we prepared thin films by SSMD using Ti-Cu as the parent alloy and Mg as the solvent. Using a multi -modal approach, we combined synchrotron X-ray spectroscopy, diffraction, and high-resolution electron -based spectroscopy and imaging to study their morphological, structural, and chemical evolution. The processing-structure relationship was analyzed as a function of parent alloy composition and dealloying temperature and time. Morphological transitions from globular, to lamellar, to bicontinuous structures, in conjunction with a ligament size evolution, were identified as functions of the parent alloy composition. The dealloying rate increased with increasing concentration of interdiffusing elements (dissolving com-ponent) in the parent alloy. The parting limit, a dealloying compositional threshold, was systematically analyzed and determined to be 30%-40%. The order of crystalline phase formation is CuMg2, Cu2Mg, and Ti; the Ti phase first shows self-reorganization during dealloying, separate from the crystallization pro-cess. The coarsening in thin-film SSMD was i dentified and not entirely self-similar; in addition to the increase of ligament size over time, the formation of larger globular ligaments were also observed. This work furthers our fundamental understanding of thin-film SSMD and nanostructured thin-film design, where the thermodynamic and kinetic effects differ from the bulk counterparts. The fact that dealloying and diffusion outpaces the crystallization and new phase formation also offers opportunities to utilize thin-film SSMD in certain alloy systems in which deleterious intermetallic phases need to be suppressed, that may not be possible in the bulk geometry. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

Thin-film solid-state metal dealloying is a promising technique for designing nanostructured thin films with diverse applications. The morphological, structural, and chemical evolution of Ti-Cu thin films prepared by SSMD using Mg as the solvent were studied using synchrotron X-ray spectroscopy, diffraction, and electron-based spectroscopy and imaging. The relationship between processing and structure was analyzed in relation to parent alloy composition, dealloying temperature, and time. Morphological transitions and the dealloying rate were found to be influenced by the parent alloy composition. The study provides fundamental insights into thin-film SSMD and offers opportunities for the suppression of undesired intermetallic phases in certain alloy systems.