Liquid Metal Dealloying in Multicomponent Systems – Towards Next-Generation Metal Composites
Embargo until
2019-08-01
Date
2018-05-10
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Publisher
Johns Hopkins University
Abstract
Liquid metal dealloying (LMD) is an emerging process for making metal composites and porous metal materials by selectively dissolving components of a parent alloy in a bath of a dissimilar metallic melt. As some fraction of the parent alloy dissolves into the liquid, the remaining solid components can be selected such that they rearrange, forming a complex structure and allowing dissolution to continue. This leads to the formation of a porous network of the solid component, with the empty space filled by solidified liquid in the final composite. Subsequently removing one phase by chemical etching reveals a porous metal structure.
In this thesis, the mechanisms of LMD and the interaction between processing methods, structural geometry, and length scale are studied in detail. We show that the thermodynamic driving force for LMD can be carefully tuned to select the final structure of the solid network that forms by changing the composition of the molten metal bath. We analyze the kinetics of the LMD process to quantify the rate of dealloying and the rate that features coarsen post-dealloying. Applying fundamental insights gained from these results, we design a dealloying system where a chemical reaction in the liquid metal forms an additional intermetallic phase within the porous network during dealloying. Finally, we present a method for making dealloyed metal coatings with superior hardness on a nickel alloy substrate, where eutectic melting at the interface between coating and substrate leads to a dealloying reaction that strengthens both materials.
Porous metals and composites made by LMD are promising for a range of applications due to the wide range of chemistries and morphologies available. This thesis seeks to address the gap in fundamental understanding of LMD mechanisms to rapidly advance the discovery, study, and application of a new generation of functional metal composites.
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Keywords
Metals, Composites, Dealloying, Liquid Metal Dealloying, Alloys, Tantalum, Niobium, Copper