Search

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]

In-situ Ti-reinforced Mg-based (MT-D) and in-situ Ta-reinforced Zr-based (ZT-D) bulk metallic glass matrix composites (BMGMCs) were prepared by a novel dealloying method, which contains an element-selective leaching process in a metallic melt. The BMGMCs exhibit better mechanical properties, including higher fracture strength and larger plastic strain, than their monolithic glassy counterparts or similar BMGMCs by ex-situ dispersing or conventional arc-melting methods. The differences of Young's modulus between the dispersoids and the glassy matrix for these BMGMCs generate stress concentration at the interface, which is considered to suppress the propagation of the single main shear band and initiate multiple shear bands to accommodate the plastic deformation. Furthermore, the fine size of dispersoids for these BMGMCs, caused by low reaction temperature during dealloying in the metallic melt, results in more interfaces with the matrix for further improvement of mechanical properties. In addition, the low reaction temperature can also contribute to less composition fluctuation of the matrix to maintain the glass-forming ability of itself, which can introduce no undesired phases to degrade the mechanical properties. This novel in-situ dealloying method is believed to make a breakthrough in designing ductile BMGMCs with fine-sized secondary particles. [ABSTRACT FROM AUTHOR]

A NiTi/Mg composite was fabricated using a method that combines top-down pore-forming and pressureless infiltration processes. The phase constituents of this simple composite are B2-NiTi, B19′-NiTi and Mg phases. Both the size and the distribution of the Mg-phase are fine and homogeneous. The composite has very high mechanical strength and damping capacity, ~1.2 and 1.5-fold higher than those of a similar composite with different microstructures, respectively. These behaviors are generally attributed to the high damping capacity of Mg, the physical continuity of the composite, and the homogeneous distribution of fine Mg-phase, which generate more interfaces, contributing to the damping capacity. This composite is considered a good candidate for use as a damping material in engineering applications. [ABSTRACT FROM AUTHOR]

Mechanical properties and fracture characteristics of Zr-based bulk metallic glass (BMG) composites containing carbon nanotube (CNT) addition were investigated in detail. The interfacial reaction between the added CNTs and the glass matrix causes the formation of some V-shape nicks on the residual CNTs. These nicks have significant effect on the mechanical properties and fracture modes of the BMG composites. The compressive fracture strength increases with increasing the volume fraction of CNT addition at first, and starts to decrease gradually when the volume fraction of CNT addition is more than 5.0%. The fracture modes of the BMG composites also change from typical shear flow deformation behavior to completely embrittling fracture gradually. The V-shape nicks originating from the interfacial reaction are responsible for the decrease of fracture strength and the variation of fracture modes. [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]

Low ductility of glassy alloys prevents their technical application as structural materials. In this work, we study the Cu-based crystal-glassy composite material with good mechanical properties. Formation of the Cu[sub 10]Zr[sub 7] phase in the glassy matrix of a high-strength Cu[sub 50]Zr[sub 30]Ti[sub 10]Nb[sub 10] bulk alloy upon solidification led to higher Young’s modulus and enhanced ductility of such a composite compared to Cu-based glassy alloys. The as-cast structure was studied by x-ray diffraction and scanning electron microscopy. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The relatively low density of Ti (4.5 Mg/m3) implies high strength/density ratio for Ti-based alloys. A composite Ti65Fe35 alloy produced in the shape of arc-melted ingot of about 20 mm in diameter and 10 mm in height exhibits a high mechanical strength of 2.2 GPa at 6.7% ductility and a Young’s modulus of 149 GPa. Its microstructure consists of the cubic TiFe phase and a supersaturated BCC β-Ti solid solution. The formation of a supersaturated β-Ti solid solution and the disperse eutectic structure obtained result in a high strength of the Ti–Fe alloy which in addition to that has much higher ductility compared to that of nanostructured and glassy alloys. The Ti–Fe alloy is characterized by low cost of the alloying elements and does not require an additional injection mould casting procedure. [Copyright &y& Elsevier]

Bulk metallic glassy composites reinforced by ZrO 2 with various volume fraction and particle size were fabricated successfully by spark plasma sintering. The compression test results indicate that mechanical property of composite is related to the particle size and volume fraction of ZrO 2 . Due to the stress concentration between the ZrO 2 and the glassy matrix, both the plastic strain and fracture strength increase firstly and then decrease with the increase of volume fraction of ZrO 2 . The deformation morphologies of composites after compression reflect the ductile–brittle transition process. [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]

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]