Biocompatible Co-P Metallic Glasses with Superior Degradation Tolerance in Physiological Environments.

Metallic glasses represent a class of metallic alloys with a fully amorphous structure and attractive properties, making them promising in bioimplant applications. Here, the degradation tolerance of biocompatible cobalt-phosphorus (Co-P) metallic glasses was studied in a simulated physiological environment. The metallic glasses were synthesized in the form of coatings through a facile electrodeposition approach. This method utilizes their outstanding surface characteristics and bypasses the size limitations usually associated with their bulk counterparts. The Co-P alloys showed exceptional tribological response with ∼14% lower coefficient of friction and 2 orders of magnitude lesser wear rate compared to SS316 stainless steel. In addition, the Co-P alloys showed a 3 times higher hardness and 4 times higher hardness/modulus ratio compared to SS316, indicating better elastic recovery under dynamic shear stresses that are common in load-bearing bioimplants. The Co-P metallic glasses exhibited excellent hemocompatibility and cytocompatibility in terms of lower platelet adhesion, spreading, and aggregation, a hemolysis ratio lower than 1%, and enhanced surface wettability, suggesting a superlative performance in bioimplant applications.

Molten Salt Corrosion Behavior of Dual-Phase High Entropy Alloy for Concentrating Solar Power Systems.

Dual-phase high entropy alloys have recently attracted widespread attention as advanced structural materials due to their unique microstructure, excellent mechanical properties, and corrosion resistance. However, their molten salt corrosion behavior has not been reported, which is critical in evaluating their application merit in the areas of concentrating solar power and nuclear energy. Here, the molten salt corrosion behavior of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) was evaluated in molten NaCl-KCl-MgCl2 salt at 450 °C and 650 °C in comparison to conventional duplex stainless steel 2205 (DS2205). The EHEA showed a significantly lower corrosion rate of ~1 mm/year at 450 °C compared to ~8 mm/year for DS2205. Similarly, EHEA showed a lower corrosion rate of ~9 mm/year at 650 °C compared to ~20 mm/year for DS2205. There was selective dissolution of the body-centered cubic phase in both the alloys, B2 in AlCoCrFeNi2.1 and α-Ferrite in DS2205. This was attributed to micro-galvanic coupling between the two phases in each alloy that was measured in terms of Volta potential difference using a scanning kelvin probe. Additionally, the work function increased with increasing temperature for AlCoCrFeNi2.1, indicating that the FCC-L12 phase acted as a barrier against further oxidation and protected the underlying BCC-B2 phase with enrichment of noble elements in the protective surface layer.

Model Metallic Glasses for Superior Electrocatalytic Performance in a Hydrogen Oxidation Reaction.

Metallic glasses or amorphous alloys, with their excellent chemical stability, disordered atomic arrangement, and ability for thermoplastic nanostructuring, show promising performance toward a range of electrocatalytic reactions in proton-exchange membrane fuel cells. However, there are knowledge gaps and a distinct lack of understanding of the role of amorphous alloy chemistry in determining their catalytic activity. Here, we demonstrate the influence of alloy chemistry and the associated electronic structure on the hydrogen oxidation reaction (HOR) activity of a systematic series of Pt42.5-xPdxCu27Ni9.5P21 bulk metallic glasses (BMGs) with x = 0 to 42.5 at%. The HOR activity and electrochemical active surface area as a function of composition were in the form of volcano plots, with a peak around equal proportion of Pt and Pd. The lower relative electron work function and higher binding energy of the Pt core level explain the reduced charge-transfer resistance and improved electrocatalytic activity due to weakened chemisorption of protons in the mid-range composition. Density functional theory calculations show the lower free energy change and higher hydrogen adsorption density for these Pt42.5-xPdxCu27Ni9.5P21 BMGs, suggesting a synergistic effect from the presence of both noble metals, Pt and Pd.

Multiscale Manufacturing of Amorphous Alloys by a Facile Electrodeposition Approach and Their Property Dependence on the Local Atomic Order.

Metallic glasses are a unique class of materials combining ultrahigh strength together with plastic-like processing ability. However, the currently used melt quenching route to obtain amorphous alloys has a high cost basis in terms of manufacturing and expensive constituent elements often necessary to achieve the glassy state, thus hindering widespread adoption. In contrast, multimaterial electrodeposition offers a low-cost and versatile alternative to obtain amorphous alloys. Here, we demonstrate multiscale manufacturing of a model binary amorphous system by a facile and scalable pulsed electrodeposition approach. The structural and mechanical characteristics of electrodeposited Ni-P metallic glasses are investigated by a combination of experiments and molecular dynamics simulations. The property dependence on slight change in alloy chemistry is explained by the fraction of short-range-order clusters and geometrically unfavorable motifs. Bicapped square antiprism polyhedra clusters with two-atom connections result in more homogeneous deformation for Ni90P10 metallic glass, whereas a relatively higher fraction of three-atom connections in Ni85P15 metallic glass leads to higher strength, albeit localized and relatively brittle failure. The practicality of our approach is likely to stimulate the use of amorphous alloys in simple chemistries for multiscale use with systematic property optimization for specific applications.

Magnetic Field Patterning of Nickel Nanowire Film Realized by Printed Precursor Inks.

This paper demonstrates an easily prepared novel material and approach to producing aligned nickel (Ni) nanowires having unique and customizable structures on a variety of substrates for electronic and magnetic applications. This is a new approach to producing printed metallic Ni structures from precursor materials, and it provides a novel technique for nanowire formation during reduction. This homogeneous solution can be printed in ambient conditions, and it forms aligned elemental Ni nanowires over large areas upon heating in the presence of a magnetic field. The use of templates or subsequent purification are not required. This technique is very flexible, and allows the preparation of unique patterns of nanowires which provides opportunities to produce structures with enhanced anisotropic electrical and magnetic properties. An example of this is the unique fabrication of aligned nanowire grids by overlaying layers of nanowires oriented at different angles with respect to each other. The resistivity of printed and cured films was found to be as low as 560 µΩ∙cm. The saturation magnetization was measured to be 30 emu∙g-1, which is comparable to bulk Ni. Magnetic anisotropy was induced with an axis along the direction of the applied magnetic field, giving soft magnetic properties.

Inkjet Printed Polyethylene Glycol as a Fugitive Ink for the Fabrication of Flexible Microfluidic Systems.

This paper demonstrates a novel and simple processing technique for the realization of scalable and flexible microfluidic microsystems by inkjet-printing polyethylene-glycol (PEG) as a sacrificial template, followed by embedding in a structural layer (e.g. soft elastomers). The printing technology allows production of an array of PEG droplets simultaneously, reducing cost and manufacturing time. The PEG can be removed through heating above its phase-change temperature after the formation of the structural layer, with hydraulic flow removing the material. The developed technique allows easy modulation of the shape and dimensions of the pattern with the ability to generate complex architectures without using lithography. The method produces robust planar and multilayer microfluidic structures that can be realized on wide range of substrates. Moreover, microfluidics can be realized on other systems (e.g. electrodes and transducers) directly without requiring any bonding or assembling steps, which often limit the materials selection in conventional microfluidic fabrication. Multilayer Polydimethylsiloxane (PDMS) microfluidic channels were created using this technique to demonstrate the capability of the concept to realize flexible microfluidic electronics, drug delivery systems, and lab-on-a-chip devices. By utilizing conductive liquid metals (i.e. EGaIn) as the filling material of the channels, flexible passive resistive components and sensors have been realized.