Search

Intermetallic compounds formed from non-precious transition metals are promising cost-effective and robust catalysts for electrochemical hydrogen production. However, the development of monolithic nanoporous intermetallics, with ample active sites and sufficient electrocatalytic activity, remains a challenge. Here we report the fabrication of nanoporous Co7Mo6 and Fe7Mo6 intermetallic compounds via liquid metal dealloying. Along with the development of three-dimensional bicontinuous open porosity, high-temperature dealloying overcomes the kinetic energy barrier, enabling the direct formation of chemically ordered intermetallic phases. Unprecedented small characteristic lengths are observed for the nanoporous intermetallic compounds, resulting from an intermetallic effect whereby the chemical ordering during nanopore formation lowers surface diffusivity and significantly suppresses the thermal coarsening of dealloyed nanostructure. The resulting ultrafine nanoporous Co7Mo6 exhibits high catalytic activity and durability in electrochemical hydrogen evolution reactions. This study sheds light on the previously unexplored intermetallic effect in dealloying and facilitates the development of advanced intermetallic catalysts for energy applications. Nanoscale intermetallic compounds are promising catalysts but the synthesis remains a challenge. The authors develop a dealloying technique to fabricate nanoporous intermetallic electrocatalysts with fine structures for efficient hydrogen production. [ABSTRACT FROM AUTHOR]

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]

Surface-activated bonding (SAB) is a direct-bonding method which joins two cleaned surfaces of similar or dissimilar materials at room or low temperature. The practicability and joint quality, however, depend strongly on the smoothness and crystallographic orientation of the bonding surfaces. Supercooled liquid metal possessing high structural homogeneity of the amorphous state and excellent near-net-shape-forming ability may resolve the shortcomings. This work proposes surface-activated supercooled liquid brazing, i.e. a modified SAB technique utilizing supercooled liquid metal as a brazing-filler material. [Copyright &y& Elsevier]

The high-entropy alloy (HEA) design strategy is effective for ultra-coarsening-resistant 3D interconnected materials developed by liquid metal dealloying (LMD). However, the fundamental understanding of the dealloying mechanism and structural evolution of multi-principal elements 3D structured materials is still missing. In this study, the microstructural evolutions of 3D interconnected HEAs in Mg matrix were investigated using two types of multiphase precursors, namely, arc-melted and homogenized ones. The precursors' microstructure greatly influences dealloying kinetics and dealloying mechanisms what, in its turn, determines the final morphology of the 3D interconnected HEAs in Mg matrix. First, the prior fcc phase was dealloyed faster than any other precursor phases at dealloying temperatures from 600 to 900 °C. Second, the dealloying kinetics was faster along precursor grain boundaries (GB) as compared with grain interior. This led to the formation of a unique layered composite structure due to the inhomogeneous dealloying along the fine lamellars' GB of the homogenized precursor. Moreover, governing orientation relationship between precursor and dealloying product depends on the LMD conditions, and it significantly affects the 3D interconnected grain structure. The fundamental understanding of the dealloying mechanisms will pave the way for customized morphology design of the 3D interconnected HEAs in metallic matrix with improved thermal stability and physical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Heat evolution of stress-induced structural disorder ΔH s(ε) of a Zr55Al10Ni5Cu30 bulk metallic glass (BMG) during compressive constant ram-velocity deformation in the glass transition region (T g =680K) was deduced from in situ measurements of temperature change ΔT(ε) of deforming samples, where ε is true strain. At transition from the linear to nonlinear viscoelasticity, i.e., a softening phenomenon, viscosity η(ε) does not change consistently with ΔT(ε) but with ΔH s(ε). Therefore, it is concluded that the stress-induced structural disorder triggered this softening phenomenon. The viscous frictional heating of the softened alloy brings about the increase in ΔT, which also influences ΔH s. Because ΔT is determined by relationship between the power of the frictional heating and heat convection to the sample-surroundings, ΔH s and η can be positively controlled with varying thermal conductivity D of the surrounding materials, especially after the transition period. [Copyright &y& Elsevier]

High-entropy nanomaterials possessing high accessible surface areas have demonstrated outstanding catalytic performance, beating that found for noble metals. In this communication, we report about the synthesis of a new, nanoporous, high-entropy alloy (HEA) possessing open porosity. The nanoporous, high-entropy Ta19.1Mo20.5Nb22.9V30Ni7.5 alloy (at%) was fabricated from a precursor (TaMoNbV)25Ni75 alloy (at%) by liquid metal dealloying using liquid magnesium (Mg). Directly after dealloying, the bicontinuous nanocomposite consisting of a Mg-rich phase and a phase with a bulk-centered cubic (bcc) structure was formed. The Mg-rich phase was removed with a 3M aqueous solution of nitric acid to obtain the open, porous, high-entropy Ta19.1Mo20.5Nb22.9V30Ni7.5 alloy (at%). The ligament size of this nanoporous HEA is about 69 ± 9 nm, indicating the high surface area in this material. [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]

Surface functionalization is an effective approach to change the surface properties of a material to achieve a specific goal such as improving the biocompatibility of the material. Here, the surface of the commercial biomedical Ti-6Al-7Nb alloy was functionalized through synthesizing of a porous surface layer by liquid metal dealloying (LMD). During LMD, the Ti-6Al-7Nb alloy is immersed in liquid magnesium (Mg) and both materials react with each other. Particularly, aluminum (Al) is selectively dissolved from the Ti-6Al-7Nb alloy into liquid Mg while titanium (Ti) and niobium (Nb) diffuse along the metal/liquid interface to form a porous structure. We demonstrate that the porous surface layer in the Ti-6Al-7Nb alloy can be successfully tailored by LMD. Furthermore, the concentration of harmful Al in this porous layer is reduced by about 48% (from 5.62 ± 0.11 wt.% to 2.95 ± 0.05 wt.%) after 30 min of dealloying at 1150 K. The properties of the porous layer (e.g., layer thickness) can be tuned by varying the dealloying conditions. In-vitro tests suggest improved bone formation on the functionalized porous surface of the Ti-6Al-7Nb alloy. [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]

Even though the Mg-based bulk metallic glasses (BMGs) have shown superior anti-corrosion properties compared with their crystalline counterparts, the brittleness of them limits the widespread application of these materials. In the present study, we have firstly introduced porous NiTi shape memory alloy particles into an Mg-Zn-Ca BMG by the direct adding method. This composite showed both improved compressive strength and corrosion resistance in Hank's solutions than its monolithic glassy counterpart. The NiTi dispersoids among the matrix were likely to hinder the main shear band propagation, and also acted as the corrosion barriers. Furthermore, the porous nature of present added particle could further increase the interface areas, which should enhance the reinforcing effects compared with solid ones. This low-cost, high-anticorrosive composite was a good candidate as an engineering material. [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]

Joining of Mg alloy to steel has received wide attention for design of multi-materials. This letter describes joining of immiscible pure iron and pure magnesium (Fe–Mg), as a simplified model, performed by solid metal dealloying (SMD) between Mg and Fe 100− x Ni x interlayers that were preliminary joined to the Fe part by diffusion bonding. SMD formed an Fe–Mg bicontinuous composite with interconnected morphology at the Fe–Mg weld interface. The effect of Ni composition x in the interlayer on the weld strength was examined. Strong joints were obtained when 30 < x < 50 at.%, which caused Mg base-metal fracture due to a well-interconnected Fe–Mg structure. When too little (x < 30 at.%) or too much (x > 60 at.%) Ni was added, interfacial fracture occurred due to limited dealloying reaction and formation of an isolated Fe product surrounded by a large amount of brittle Mg 2 Ni. [Display omitted] [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]

Nanoporous non-noble metals with attractive properties can be fabricated by liquid metal dealloying (LMD). However, further refinement of the ligament size of nanoporous metals produced by LMD is desired because this high-temperature process induces rapid ligament coarsening. Herein, we fabricate nanoporous refractory metals and alloys by LMD. The molybdenum (Mo)-tantalum (Ta) alloy with the smallest ligament size of the specimens contains a B2 ordered structure, whereas the other specimens possess disordered structures. It is proposed that the B2 ordering of the Mo-Ta alloy suppresses ligament coarsening by restricting the surface diffusion of atoms during LMD. The Mo-Ta alloy with B2 ordered structure exists in a previously inaccessible low-temperature region of the related phase diagram, illustrating that LMD can enable access to new materials. Our results indicate that materials with refined ligaments may be obtained by LMD promoting the formation of ordered structures. [Display omitted] [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]

We designed a new microstructure control method (liquid metal replacement method) that creates entirely new composites using the original microstructure as a template. This method selectively replaces a specific phase from a composite with another phase based on differences in atomic interactions. We applied this method to the dissimilar material joining of immiscible titanium and magnesium. After diffusion bonding one side of an interlayer consisting of α-Ti / α-Sc phases to Ti, we butted the opposite side with Mg and reheated. At this interface, selective interdiffusion of Mg and Sc results in the replacement of only the α-Sc phase by the α-Mg phase, forming a new α-Ti / α-Mg bicontinuous microstructure using the α-Ti / α-Sc monotectoid microstructure as a template. The Sc that diffused to the Mg side formed a reaction layer where the MgSc (B2) and (Mg, Sc) solid solution coexisted. These novel composite structures and reaction layers strengthened the joint area. As a result, we suppressed fracture at the joint interface, causing fracture at Mg and achieving a maximum joint strength of 116 MPa. [Display omitted] • We welded dissimilar titanium and magnesium through a scandium-containing interlayer. • The magnesium melts selectively replaced specific phases of the Ti/Sc microstructure. • A three-dimensional bicontinuous microstructure of immiscible Ti/Mg phases formed at the joint interface. • We studied the relationship between the interlayer composition and tensile strength. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) interconnected heterogeneous composites prepared through liquid metal dealloying (LMD) have been studied owing to their unique structural features and interesting deformation behavior beyond the strength-ductility trade-off. In this work, we systematically investigated the abrasive wear mechanism of 3D interconnected composites comprising immiscible Mg and Fe 80 Cr 20 as a function of the fraction of hard Fe 80 Cr 20 phase. (Fe 80 Cr 20) x Ni 100−x precursor alloys were used in the LMD process, and the miscible Ni element dissolved in the Mg melt. Subsequently, the self-organization of the solid Fe 80 Cr 20 led to a 3D interconnected composite containing penetrated Mg structures. The volume fraction of Mg phase and microstructural features of the composites were highly influenced by the initial Ni concentration. Although the composites had a brittle interface because of the immiscibility of Mg and Fe 80 Cr 20 , the 3D interconnected structures exhibited exceptional abrasive wear resistance beyond expectations. Highly deformed structures were observed on worn surfaces, and wear mechanisms differed from those of bulk Mg and Fe 80 Cr 20 materials. During the wear test, the area fraction of Fe 80 Cr 20 phase on the worn surface increased significantly, and the presence of nanograined Fe 80 Cr 20 layers with a high dislocation density effectively protected the underlying soft Mg phase. In particular, the Mg-based tribofilm acted as a lubricant in the 3D interconnected structure. These findings related to the improvement of wear resistance through structural design could serve as guidelines for various applications of heterogeneous 3D architecture materials. [Display omitted] • LMD process was applied to synthesize 3D interconnected Mg-Fe 80 Cr 20 composites. • 3D interconnected composite structures are effective against abrasive wear. • Highly deformed worn surface with nanograined structure was formed after wear. • The fraction of Fe 80 Cr 20 phase on the worn surface was significantly increased. • Nano-grained Fe 80 Cr 20 layers beneficially protected the underlying soft Mg phase. [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 Liquid metal dealloying is a promising technique to get nanoporous materials which are attractive for their excellent functional properties. From a (FeCr) x -Ni 1−x precursor, it is possible to get porous FeCr with this technique. While immersing precursors in a molten Mg bath, Ni atoms selectively migrate into the Mg bath. After cooling down to room temperature, the resulting microstructure is a bi-continuous structure of FeCr and Mg (with Ni in solid solution). A final etching step removes the Mg solid-state solution phase. Precursors with different compositions were dealloyed and imaged in 3D. From X-ray tomography images, porous FeCr characteristics as solid fraction, phase size, specific surface were extracted. EBSD maps were acquired on samples before and after dealloying. We will show that precursor composition is a key parameter to control pores and grains size while dealloying parameters (time and temperature) are key parameters to control ligaments size and in fine specific surface. By controlling precursor composition and dealloying parameters it is now possible to get dealloyed nanoporous metals with desired grain and porous microstructure by liquid metal dealloying. Highlights • FeCr-Ni precursors were dealloyed in a Mg bath to give FeCr-Mg bicontinuous structure. • FeCr-Mg bicontinuous structure was immersed in HNO 3 solution to get porous FeCr. • (FeCr) x -Ni 1−x precursors are fully FCC phase while porous FeCr are fully BCC phase. • Composition & dealloying parameters are key parameters for controlling microstructure [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]

Metallic glass (MG) exhibits viscous flow behavior in the supercooled liquid (SCL) state, which is of great advantage for its net-forming process. However, the viscous workability varies strongly with the alloy system and/or composition. In this paper, we demonstrate how MG with less viscous workability such as Gd-based MG can be processed in the SCL region. Based on this understanding, high aspect ratio analyzer gratings of 9 μm pitch and ∼30 μm heights have been fabricated through an imprinting method by allowing crystallization during a rapid heating isochronal imprinting process. The analyzer gratings made of Gd-based MG have brought a breakthrough for advancing neutron phase imaging based on grating interferometer. [ABSTRACT FROM AUTHOR]

A breakthrough in the strength and ductility trade-off is crucial for the development of advanced metallic materials. Herein, we present a novel heterostructured composite composed of immiscible magnesium (Mg) and ferrochrome (FeCr) with a 3D interconnected morphology and synthesized by liquid metal dealloying. Soft Mg and hard FeCr zones mutually interlock with each other. This unique interpenetrating-phase configuration leads to a significant alternation of their intrinsic mechanical properties, especially in the soft Mg zone. It causes a strong forest hardening effect, resulting in a high initial dislocation density, and the surrounding hard zones create hydrostatic pressure at the soft zone under tension. The measured yield strength of the composite is close to the upper rule of mixture while its tensile elongation is larger than that of the mixture. These outstanding mechanical properties originate from the synergetic interaction between the soft and hard zones through the immiscible interface zone. The current 3D interconnected heterogeneous composite acts a guideline for the design of advanced materials possessing physical properties beyond expectations. [Display omitted] [ABSTRACT FROM AUTHOR]

Low modulus biomaterials are in focus as potential candidates for biomedical implants ensuring a fast healing of hard tissues. The close match between elastic properties of an implant material and bone are critical to eliminate stress-shielding effect. In this study, we synthesized a low modulus interpenetrating-phase composite of Ti and Mg by liquid metal dealloying. Its Young's modulus value is in the range of that found for human bone which allows for biomedical applications of this material. Unexpectedly, the Young's modulus value of the composite (17.6 GPa) is several times lower than that of each individual constituent phases, namely, Mg (45 GPa) and Ti (110 GPa). Using micromechanical modelling, it is demonstrated that the origin of the anomalously low modulus can be related to a weakened interface between the constituents. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• 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]