Kinetics and morphological evolution of liquid metal dealloying

Abstract

Liquid metal dealloying (LMD) has recently emerged as a novel technique to fabricate bulk nanostructures using a bottom-up self-organization method, but the literature lacks fundamental studies of this kinetic process. In this work, we conduct an in-depth study of the kinetics and fundamental microstructure evolution mechanisms during LMD using Ti-Ta alloys immersed in molten Cu as a model system. We develop a model of LMD kinetics based on a quantitative characterization of the effects of key parameters in our system including alloy composition, dealloying duration, and dealloying temperature. This work demonstrates that the dealloying interface is at or near equilibrium during LMD, and that the rate-limiting step is the liquidstate diffusion of dissolving atoms away from the dealloying interface (diffusion-limited kinetics). The quantitative comparison between theoretically predicted and measured dealloying rates further reveals that convective transport and rejection of the dissolving element during coarsening of the structure also influence the dealloying kinetics.

Beating Thermal Coarsening in Nanoporous Materials via High‐Entropy Design

“…Coarsening kinetics of 3DNP HEA is drastically minimized at elevated temperatures ( Figure a,b). Using an Arrhenius‐type equation on the diffusivity and ligament size, the coarsening component, n , is determined to be 3.44–3.61, which is close to the kinetic parameter, ≈4, reflecting surface diffusion. Thus, surface diffusion governs the coarsening of the 3DNP HEA, as in the conventional porous metals .…”

Phase-field investigation of the coarsening of porous structures by surface diffusion

“…Recently, this limitation has been overcome with the development of liquid metal dealloying, that consists in using a molten metal to selectively dissolve one component out of a binary alloy [12]. This processing technique presents the advantage of being applicable to a wide range of metals including titanium [13], iron [14], niobium [15], and tantalum [16,17], or semiconductors such as silicon [18]. Also, comparable porous structures have been obtained from vapor phase dealloying that relies on the low partial pressure of one of the component of the alloy to trigger selective dissolution [19,20].…”

“…This coarsening process is important to control and limit as much as possible because it leads to a severe decrease of the specific surface area and therefore to a drop of materials properties. Common strategies consist of decreasing the surface diffusion by reducing the dealloying temperature [15,17,23] or adding impurities that reduce surface diffusivity [24,25].…”

Challenges and Opportunities for Integrating Dealloying Methods into Additive Manufacturing

“…This phenomenon was first discovered by Harrison and Wagner in 1959 [ 16 ] and was re-introduced by Wada et al in 2011 [ 17 , 18 ]. Since then, considerable literature has been published on the kinetics of the process and the application of this technique to dealloy materials that cannot be dealloyed electrochemically [ 19 , 20 ], for instance, Ti and refractory metals, which were previously inaccessible due to their relatively low surface mobilities [ 21 ]. To date, liquid metal dealloying has been used to make bicontinuous porous structures of Nb [ 22 , 23 , 24 ], Ti [ 25 ], C [ 26 ], stainless steel [ 27 ] and Co-based alloys [ 28 , 29 ].…”

“…However, the dissolving element has decreased solubility in molten eutectic alloys compared to its solubility in single-element solvents, drastically slowing dealloying. McCue et al discussed how, due to this reduced solubility, they were unable to fully dealloy bulk samples using eutectic alloy baths, only reaching a dealloying depth of 150 μm after 60 min [ 19 ] The diffusion limitations in the dealloying medium through the dealloyed region became too severe. In contrast, the diameter of most AM powders is much smaller, so this issue with bulk samples can be also be avoided.…”