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Liquid metal dealloying (LMD) is a new technology to create porous materials. From a (FeCr)x‐Ni1–x precursor, it is possible to get a bicontinuous structure of FeCr and Mg: a metal–metal composite. An etching step removes the Mg solid‐state solution phase to give a metal–air composite. The last step, polymer infiltration, gives metal–polymer composites. Herein, metal–metal, metal–air, and metal–polymer (rubbery or glassy polymers) with three different phase ratios are elaborated by LMD from Ni‐based precursors and their mechanical properties are analyzed. A full polymer infiltration into the pores is obtained and the epoxy polymer properties are not affected by the metallic foam presence. Concerning control of the mechanical properties, the material's second‐phase selection is a key factor. Herein, it is shown that the mechanical properties are easily designed by optimizing phase ratio, ligament size, and second‐phase type and that these materials are promising materials for biomedical applications. [ABSTRACT FROM AUTHOR]

Liquid metal dealloying is a new process that can be applied to synthesize non-noble porous materials by preventing oxidation in a utilized metallic melt. The effect of dealloying rate was investigated by electron backscattered diffraction at the reaction layer at various temperatures (600–800 °C) using (FeCo) x Ni 100− x precursors in a Mg melt. FeCo ligaments transformed via different mechanisms depending on dealloying rate, temperature, and concentration of Ni. At the initial stage near the precursor surface, random texture was dominant in all cases. When the dealloying rate slowed down at 600 °C and 800 °C, the parent face-centered cubic grain structure played a significant role. The second stage differed depending on the dealloying conditions, including formation of <111>//normal direction fiber texture or an unknown specific orientation relationship. The orientation relationships also differed in the third stage. At 800 °C, the dealloying rate should be much slower than that at 600 °C to appear the third stage of the specific orientation relationship. • Dealloying rate strongly influences transformation mechanism in liquid metal dealloying. • When the dealloying rate is very high, random texture normally develops. • Ni70 showed a larger extended first stage of random texture than Ni30 and Ni50. • Governing orientation relationship depended on dealloying rate of Ni50 at 600 °C. • At 800 °C, fiber texture altered to an orientation relationship when dealloying rate decreased. [ABSTRACT FROM AUTHOR]

Liquid metal dealloying (LMD) is a promising technique that can be used to synthesize non-noble porous materials by preventing oxidation through using a metallic melt. However, the phase transformation behavior between a parent grain and synthesized ligaments surrounded by penetrating liquid metal channels remains unknown, despite its importance on the final physical properties. In this study, the temperature effect on the transformation mechanisms during the LMD process is investigated. At a low temperature of 600 °C, a fcc grain of (FeCo) x Ni 100− x precursors transforms to bcc FeCo ligaments by following unique orientation relationships (ORs), which differ from the well-known ORs like Bain, Kurdjumov-Sachs and Nishiyama-Wassermann. A few select variants are generated in the proposed ORs, and the formation of coincident site lattice boundaries is shown to play a crucial role in the variant selection to reduce the internal energy of the initial nanostructure. However, at a higher temperature of 800 °C, the crystal orientation of ligaments prefers to align in the <111> direction, which is parallel to the flow direction of Mg melt, owing to a strong interaction between the melt and ligaments. Ligaments are elongated along with the fiber texture, and this transformation behavior is irrelevant to the parent orientation. Image 1 • Governing orientation relationships during liquid metal dealloying were revealed. • Transformation mechanism varied depending on the dealloying temperature. • At 600 °C, the suggested ORs are rotated by 35.3°, 40.5°, and 45.1° from the KS OR. • Only a few variants were transformed from one parent fcc grain to bcc ligaments. • The formation of CSL boundaries play a crucial role in the variant selection. [ABSTRACT FROM AUTHOR]

Three-dimensional interconnected nanoporous FeCo can be prepared by liquid metal dealloying. This study investigates the surface morphology and ordering kinetics of three-dimensional interconnected nanoporous FeCo. The chemical composition and dealloying temperature mutually influence the surface structure of the ligament scaffold. The ordering kinetics are accelerated by the surface-diffusion-driven coarsening in the nanoporous structure. Post-heat treatment leads to the development of precise nanofacets via the preferential growth of surface planes. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A hierarchical porous metal has been prepared by two-step liquid metal dealloying using an alloy precursor containing two soluble components and two metal baths. After the first dealloying step, one of the soluble components is dissolved and a coarse porous structure is formed. After a shorter dealloying step in another melt, the other soluble component is dissolved and a fine porous structure is formed within the previously formed coarse ligaments. The resultant porous metal presents a hierarchical morphology with a bimodal pore distribution, resulting in a higher porosity and surface-area-to-volume ratio than what can be formed by one-step dealloying methods. [ABSTRACT FROM AUTHOR]

Porous NiTi shape-memory-alloy particle-reinforced Mg-based bulk metallic glass matrix composites were prepared by an ex-situ method. The composites show a larger plastic strain, higher fracture strength and obvious work-hardening behavior compared with their monolithic glassy counterparts. The ex-situ porous NiTi particles hinder the rapid propagation of shear bands, which generates multiplied shear bands, like other ductile metal particles, and undergo a stress-induced martensitic transformation, which is unique and contributes to work hardening. Local regions within one porous particle satisfy the optimal conditions of bulk metallic glass matrix composite structure, i.e., the average particle size and mean inter-particle spacing are close to the processing zone size, and thereby further improve the plasticity by localized plastic deformation. [ABSTRACT FROM AUTHOR]

The solid dealloying reaction was investigated using (Fe,Cr)-Ni and Mg diffusion couples. Ni selectively reacted with Mg and the remaining Fe and Cr formed various topologies. An etching treatment provided interconnected Fe–Cr alloy with a ligament width below 200 nm, which is about one order of magnitude finer than that obtained for dealloying with Mg melt. The formation of ordered single-crystal nanofilaments at the dealloying front suggests that the topology evolved via the recently proposed interfacial spinodal decomposition and diffusion-coupled growth mechanism. [ABSTRACT FROM AUTHOR]

Liquid metal dealloying is a promising technique to elaborate porous metallic materials with potential applications for catalysis and energy storage. It consists in the selective dissolution of an element out of a precursor alloy by immersing it in a liquid bath. To model this process, we introduce a one-dimensional diffusion model that relies on the thermodynamic properties of the ternary system, and on a maximum velocity criterion of the reaction front. The model is compared to experimental measurements conducted on NiCu samples dealloyed in liquid Ag. Regarding the kinetics, the model enables to reach experimental time-scales, replicate experimental trends, and reveal the influence of the ligament structure on the dealloying rate. Also, by assuming thermodynamic equilibria between solid and liquid phases in the dealloyed region, the microstructure gradient obtained numerically is in satisfactory agreement with experimental measurements. These numerical results are obtained without adjustable parameters, which opens the possibility to predict dealloyed microstructures as function of the process parameters (precursor and bath composition, dealloying time and temperature, etc.). [Display omitted] [ABSTRACT FROM AUTHOR]

Liquid metal dealloying is a promising technique for synthesizing non-noble porous materials by preventing oxidation in a metallic melt. This method considers the heats of mixing between precursor elements and a melt element to design miscible and immiscible elements for a precursor. In this study, Ni and Co were selected as the miscible elements in an Mg melt as constituents of (FeCo) 100− x Ni x precursor alloys to understand the complex mechanisms of their dissolution behavior. Dissolution of the second miscible element, Co, was governed by the composition of the Mg melt, because the characteristics of the melt changed in the presence of a high amount of dissolved Ni and its convection. The synthesized FeCo ligaments showed morphology variations depending on the dealloying temperature: the ligaments become more elongated along the dealloying direction at higher temperatures. A double-gyroid-like porous structure with a narrow liquid channel, produced from the (FeCo) 70 Ni 30 precursor, exhibited the highest specific surface area at all processing temperatures from 600 °C to 800 °C. This structure differed completely from that of the typical porous Fe 80 Cr 20 alloy produced under the same liquid metal dealloying conditions. Elongation resulted from time-dependent directional coarsening behavior that was affected by the composition of the Mg melt. Unlabelled Image • First demonstration of 3D interconnected porous FeCo materials produced by liquid metal dealloying • Ligament morphology depends on ordering and coarsening mechanisms at different temperatures. • Strong interaction between FeCo ligaments and the Mg melt affected coarsening behavior. • Double-gyroid-like structure showed the highest specific surface area. • Prerequisite conditions for dissolution of the second miscible element are identified. [ABSTRACT FROM AUTHOR]

Abstract Liquids metal dealloying is a new technology to create porous materials. In this study, a commercial Incoloy 825 nickel superalloy is dealloyed for 1 h at 3 different temperatures to elaborate a fully porous FeCr-based metal with 3 different porous microstructures. The resulting porous metals showed unimodal pore distribution, hierarchical structure or, contain large ligaments inclusions. The passivation ability of the porous material was conformed irrespective of the microstructure. This letter proves the possibility of fabricating low cost high specific surface materials for electrochemical applications. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

To obtain anisotropic nanoporous NiCr , some NiCr-Ag composites were prepared using a liquid metal dealloying method and were cold rolled before etching. While immersing (Ni 90 Cr 10 ) 60 Cu 40 precursors in a molten Ag bath, Cu atoms selectively migrate into the Ag bath. After cooling down to room temperature, the resulting microstructure is a bi-continuous structure of NiCr and A g (with Cu in solid solution). These ingots are strong enough to be cold rolled in one or two (perpendicular) directions with a thickness reduction of 70%. A final etching step removes the A g solid-state solution phase. The influence of cold rolling on the microstructure was investigated using X-ray tomography and on the mechanical properties using nanoindentation. We will show how introducing anisotropy into the microstructure and in the mechanical properties was successful while being able to preserve the porous state. [ABSTRACT FROM AUTHOR]

To increase the surface area while decreasing the ligament size of an Nb anode pellet for use as a capacitor, we added Ce to an Mg melt; the dealloying reaction occurred at temperatures lower than 1023 K, the previously lowest recorded temperature for such a reaction. By analyzing the dealloying kinetics, we found the optimum dealloying conditions to produce a minimum ligament size of 100 nm in the Mg 95.7 Ce 4.3 melt: 923 K for 420 s. Using these conditions, we increased the specific surface area of the Nb anode pellet to 4.3 m 2 /g, which increased its mass-specific capacitance to 875,000 μFV/g. [ABSTRACT FROM AUTHOR]

The transition behavior from a Nb–Ni precursor to porous Nb and the coarsening of ligaments by a dealloying reaction in a Mg melt are investigated. Based on these results, the kinetics of the reaction are discussed. When a Nb 25 Ni 75 (at.%) disk was immersed in a Mg melt, the Ni content decreased the most at the surface of the disk and less so towards the interior of the disk. In this disk, it was found that transition layers of body-centered cubic-Nb and Ni 6 Nb 7 formed. These transition layers grew, following a parabolic law, and the activation energy of such growth was close to values reported for the diffusion of solute atoms in liquids, suggesting that diffusion of Ni in the Mg melt was the rate-controlling process of the dealloying reaction. The ligament size depended on time and temperature, following a power law with an exponent of 4, suggesting that surface diffusion was a key part of coarsening. These results agree well with those reported for conventional dealloying in an aqueous solution. Based on the kinetics analyses, the dealloying conditions were optimized to maximize the specific surface area, allowing a Nb electrolytic capacitor to be produced with a maximum mass-specific capacitance of 650,000 μFV g −1 , about three times larger than the highest value previously reported. [ABSTRACT FROM AUTHOR]

Abstract: Porous Nb was prepared by dealloying in a metallic melt. A Ni–Nb precursor was immersed in a Mg melt, and Ni was selectively dissolved into the melt. The remaining Nb self-organized into a bicontinuous structure. Removing the Mg solvent in aqueous HNO3 yielded open-cell sub-μm porous Nb, which was applied in solid electrolytic capacitors after anodization. Ligament size decreased with decreasing immersion time. This increased the mass-specific capacitance to 500,000μFV/g, by increasing the specific surface area to 3.92m2/g. [Copyright &y& Elsevier]

Abstract: A Mg3Cu3Gd bulk metallic glass matrix composite with porous α-Ti dispersoids was prepared by dealloying in a metallic melt. The in situ formed α-Ti dispersoids had a pore-size of ∼500nm, which was imparted from the Ti2Cu precipitate in the prealloy. Pore size was therefore controllable through the cooling rate of the prealloy preparation. Plasticity was not improved apparently, however the maximum fracture stress under four point bending mode increased from 217MPa for the monolithic counterpart to 387MPa. This was due to the optimal relationship where dispersoid size (L)≈dispersoid interval distance (S)≈process zone size (R p ). This was achieved locally within and around the porous Ti dispersoids, and helped improve the toughness and ductility. [Copyright &y& Elsevier]

Dealloying in metallic melts has been used to prepare pure base metals with an open-cell porous structure, an example of which is Ti. In this study, previously suggested strategies have been extended to prepare a porous multicomponent Ti alloy of non-equilibrium body-centered cubic phase at room temperature. Dealloying in metallic melts is a promising method for preparing functional nano- to submicro-porous alloys which cannot be prepared by conventional methods. [ABSTRACT FROM AUTHOR]

Abstract: Dealloying, which commonly involves corrosion processes in aqueous solutions, is a promising technique for preparing functional nanoporous metals. While this technique is ideal for preparing nanoporous noble metals such as of Au, it is not readily applicable to less-noble metals. Here, we propose a novel dealloying method employing a metallic melt, instead of an aqueous solution, as the dealloying liquid for a preparing of nanoporous metals. An atomic interaction among alloy components and metallic melt causes specific component to dissolve out from the alloy solid into the melt with self-organizing nanoporous structure by the remaining component. The dealloying method can be applied for preparation of nanoporous less-noble metal such as of Ti for the development of functional materials such as fluid filters, gas absorption media, and biomaterials. [Copyright &y& Elsevier]

• Microporous ferritic stainless steel was produced from Incoloy 800 via LMD. • LMD can be used industrially to produce inexpensive porous materials. • Minor elements in commercial alloys tend to slow down coarsening kinetics. • Nitric acid that serves for Mg dissolution also induces a passivation treatment. • The pore size (0.5–1.5 μm) has no significant effect on pitting sensitivity. • The pore size plays a role on diffusion processes through the porous structure. Liquid metal dealloying is a newly available technology used to create bulk porous materials. In this study, a commercial nickel-based superalloy, Incoloy 800, was dealloyed to elaborate a fully porous ferritic stainless steel. The Mg selective dissolution in nitric acid solution acts as a passivation treatment that enhances the passive film resistance. Corrosion tests confirm the beneficial effect of the nitric acid treatment on the Cr enrichment of the passive film thus improved the material resistance. The electrochemical characterizations show a higher effect of the size porosities on the diffusion kinetics of the electrolyte rather than on the pitting sensitivity. [ABSTRACT FROM AUTHOR]