Self-organizing Nano-architectured Materials: Synthesis: Diffusion-Coupled Growth
Program Organizers: Yu-chen Karen Chen-Wiegart, Stony Brook University / Brookhaven National Laboratory; Ian Mccue, Northwestern University; Erica Lilleodden, Fraunhofer Insitute for Microstructure of Materials and Systems (IMWS); Pierre-Antoine Geslin, CNRS / INSA-Lyon; Qing Chen, Hong Kong University of Science & Technology
Monday 2:00 PM
February 28, 2022
Location: Anaheim Convention Center
Session Chair: Ian Mccue, Northwestern University; Erica Lilleodden, Fraunhofer Insitute for Microstructure of Materials and Systems (IMWS)
2:00 PM Invited
Bicontinuous Structure Formation by Peritectic Melting: Mingwang Zhong1; Longhai Lai1; Alain Karma1; 1Northeastern University
Dealloying is by now a well-established synthesis method to produce open nanoporous or bicontinuous structures. Most dealloying methods explored to date, from electrochemical to liquid metal and vapor phase dealloying, involve the selective dissolution of one element of a base alloy into a dealloying medium such as an electrolyte, a liquid metal, or a vapor. Recent experiments have suggested that bicontinuous structures can also be produced by simply melting a binary peritectic alloy without the need of a dealloying medium. However, the mechanism of dealloying in this case remains unclear. This talk will present the results of a phase-field modeling study of peritectic melting of Ti-Ag alloys. The results reproduce the observed formation of interpenetrating Ag-rich and Ti-rich phases and shed light on the mechanism of nano-/micro-structural pattern formation by peritectic melting. Similarities and differences between liquid metal dealloying and peritectic melting will be emphasized.
Oriented Nanoporous Metal via Reduction-induced Decomposition: Congcheng Wang1; Qing Chen1; 1Hong Kong University of Science & Technology
The interface-controlled dissolution kinetics in dealloying generates invariantly randomly oriented pores at nanoscales. We show that in a dealloying-analogy, reduction-induced decomposition, the high rate of selective dissolution reaches the limit of diffusion in the liquid solution, and thereby aligns the nanoporous structure with the propagation of reaction. The underlying mechanism is explained via in-situ measurements of instantaneous reaction rates and activation energies. We further demonstrate that with a flow field guiding the ingression of the solution, we can manipulate the structural orientation to create complex orientation patterns for applications as electrodes in flow cells.
Coupled Coarsening and Dissolution Kinetics during Liquid Metal Dealloying: Longhai Lai1; Bernard Gaskey2; Alyssa Chuang2; Jonah Erlebacher2; Alain Karma1; 1Northeastern University; 2Johns Hopkins University
Liquid metal dealloying is an established synthesis method to produce bicontinuous structures of two interpenetrating phases by selective dissolution of one alloy element into a metal bath. To date, coarsening of the solid structure behind the dealloying front has been assumed to be controlled by diffusion confined at the solid-liquid interface, in direct analogy with surface diffusion in electrochemical dealloying. We present phase-field simulation and experimental results demonstrating that the coarsening kinetics is strongly influenced by bulk diffusion in the liquid due to the small, albeit finite, solubility of the immiscible alloy element. Liquid-state diffusion causes simultaneous coarsening and dissolution of the ligaments and a dramatic reduction of the genus of the solid structure when the solid fraction is sufficiently reduced. We demonstrate that the coarsening kinetics and the genus can be controlled by varying the solubility of the immiscible element by the choice of bath composition.
Nanoporous Refractory Multi-principal Element Alloy Thin Films for Higher Temperature Application Fabricated by Vacuum Thermal Dealloying: Tibra Das Gupta1; Thomas Balk1; 1University of Kentucky
Nanoporous structures with 3D interconnected networks are traditionally made by dealloying a binary precursor. Certain approaches for fabricating these materials have been applied to refractory multi-principal element alloys (RMPEAs), which can be suitable candidates for higher temperature applications. In this study, nanoporous refractory multi-principal element alloys (np-RMPEAs) were fabricated using single- and multi-layered magnesium-based thin films (VMoNbTaMg) that had been magnetron sputtered. Vacuum thermal dealloying (VTD), which involves sublimation of a higher vapor pressure element, is a novel technique for synthesizing these nanoporous refractory elements that are prone to oxidation. When VMoNbTaMg was heated under vacuum, a nanoporous structure was created by sublimation of the highest vapor pressure element (Mg). XPS depth profiling indicated less ligament oxidation during VTD as compared to traditional dealloying methods. np-RMPEAs exhibited outstanding stability against coarsening, retaining smaller ligaments (~25-30 nm) at higher temperature (700˚C) for a prolonged period (48 hours).
3:30 PM Break
Powder-based Dealloying: Scalable Synthesis of Porous Refractory Alloys: Alyssa Chuang1; Ian McCue2; Jonah Erlebacher1; 1Johns Hopkins University; 2Johns Hopkins Applied Physics Laboratory
Dealloying refractory alloys requires the use of a molten metal solvent to produce the characteristic self-organized porous morphologies associated with selective dissolution. This process is challenging to scale up because the velocity of the dealloying front is limited by diffusion of the dissolving species away from the reaction front. Powder-based dealloying is a promising approach to reduce the diffusion distance of the dissolving species to the radius of a single powder particle by adapting the dealloying environment to a two-component powder mixture. Here we present a study of the solid metal and liquid metal dealloying kinetics of the two-component powder system comprising TaTi as the parent alloy powder and Cu as the solvent powder. By tailoring the processing conditions and TaTi:Cu ratio, we can synthesize a wide spectrum of microstructures using powder-based dealloying and apply our findings to laser-based additive manufacturing.
Grain Boundary Effects in Liquid Metal Dealloying: A Phase Field Study: Nathan Bieberdorf1; Laurent Capolungo2; Mark Asta1; 1University of California Berkeley; 2Los Alamos National Laboratory
Nano-porous metals processing by dealloying is very sensitive to the microstructure of the base alloy. In particular, grain boundaries have been observed to significantly vary the parting limit and final ligament morphology in nano-porous dealloyed metals. However, fundamental understanding of the mechanisms by which grain boundaries influence the dealloying process remains incomplete. Here, we use phase-field modeling to study the effects of grain boundaries in model liquid-metal dealloying systems. We find that localized dissolution and grain boundary migration are key mechanisms to dealloying polycrystalline metals, and these mechanisms are controlled by grain boundary properties such as mobility, diffusivity, and energy (all of which are expected to vary with grain-boundary character). Implications of the results for dealloying by different methods will be discussed.
Process-structure Relationships in Nanoporous Gold Dealloying and Sources of Its Synthesis Variability: Stanislau Niauzorau1; Aliaksandr Sharstniou1; Natalya Kublik1; Bruno Azeredo1; 1Arizona State University
A recent spike of interest in nanoporous gold applications where its properties can be successfully exploited promoted the dealloying community to take a closer look at its process-structure relationships to achieve a better control over its morphology as it was proven to strongly regulate its properties. In this study, the process-structure relationships were established for nanoporous gold fabricated by electroless chemical dealloying of nanocrystalline AuAg thin films and it was found that the variability can be introduced (i) by the difference in equilibration time, which results in different solution evaporation rates and open circuit potential fluctuation, and (ii) by aging of precursor thin film in ambient and inert environments, which can promote its oxidation and tarnishing along with a grain growth. Additionally, it was found that the residual silver content in nanoporous gold can serve as a better predictor of the ligament diameter rather than dealloying time.