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The sluggish oxygen evolution reaction (OER) remains a major bottleneck in hydrogen generation through electrolysis, particularly in large current operations. Thus, there is a huge interest in the development of highly active and robust non-noble metal-based OER catalysts. Herein, we report excellent catalytic performance of oxygen vacancy enriched, nano-porous Mn3O4/Ni/NiMnO3 architecture, synthesized in situ over a NiMn substrate through high-rate straining and chemical dealloying. The multiphase active surface exhibits significantly low overpotentials of only 262 mV and 282 mV even at high current densities of 500 mA cm−2 and 1000 mA cm−2, respectively. Our first-principles analysis revealed the prevalence of multi-site lattice oxygen-mediated pathways with two parallel mechanisms of direct evolution of O2, (a) facile cleavage of Ni–O bonds at the NiMnO3 surface and release of lattice oxygen and (b) activation of under-coordinated Mn–O polyhedra at the Ni/NiMnO3 interface and cleavage of OH groups by protonation of surface O atoms. The presence of oxygen vacancies leads to electronic reconstruction, further enhancing the adsorption kinetics of reaction intermediates. [ABSTRACT FROM AUTHOR]

Magic-angle twisted bilayer graphene (TBG), with rotational misalignment close to 1.1 degrees, features isolated flat electronic bands that host a rich phase diagram of correlated insulating, superconducting, ferromagnetic and topological phases.sup.1-6. Correlated insulators and superconductivity have been previously observed only for angles within 0.1 degree of the magic angle and occur in adjacent or overlapping electron-density ranges; nevertheless, the origins of these states and the relation between them remain unclear, owing to their sensitivity to microscopic details. Beyond twist angle and strain, the dependence of the TBG phase diagram on the alignment.sup.4,6 and thickness of the insulating hexagonal boron nitride (hBN).sup.7,8 used to encapsulate the graphene sheets indicates the importance of the microscopic dielectric environment. Here we show that adding an insulating tungsten diselenide (WSe.sub.2) monolayer between the hBN and the TBG stabilizes superconductivity at twist angles much smaller than the magic angle. For the smallest twist angle of 0.79 degrees, superconductivity is still observed despite the TBG exhibiting metallic behaviour across the whole range of electron densities. Finite-magnetic-field measurements further reveal weak antilocalization signatures as well as breaking of fourfold spin-valley symmetry, consistent with spin-orbit coupling induced in the TBG via its proximity to WSe.sub.2. Our results constrain theoretical explanations for the emergence of superconductivity in TBG and open up avenues towards engineering quantum phases in moiré systems. Placing a single layer of tungsten diselenide in contact with twisted bilayer graphene enables superconductivity even for non-magic twist angles where insulating behavior is absent., Author(s): Harpreet Singh Arora [sup.1] [sup.2] , Robert Polski [sup.1] [sup.2] , Yiran Zhang [sup.1] [sup.2] [sup.3] , Alex Thomson [sup.2] [sup.3] [sup.4] , Youngjoon Choi [sup.1] [sup.2] [sup.3] , [...]

Alteration in the morphology of layered materials to improve storage capacity for electrical energy storage (EES) systems, including supercapacitors (SCs), provides enormous opportunities to impart unique structural features and tunable electrochemical properties. Herein, we prepared VS4@CNF heterostructures via a solvothermal process where in situ growth of VS4 (vanadium tetrasulfide) occurred at the CNF (carbon nanofiber) surface. Variation in the relative weight percentage of CNF to VS4 (as VS4@CNFx/2x/3x) affected the morphology of the grown VS4 from nanosheets to micro-flower. The as-synthesized VS4@CNFs composite was investigated as the active electrode material for SCs. Growth of layered VS4 at the CNF surface added advantages to the resulting materials by improving the conductivity as well as the charge acceptor sites during the SC cycling process. A concomitant hybrid morphology VS4@CNF2x electrode demonstrated excellent electrochemical performance, with a specific capacitance of 840 F g−1 at 1 A g−1 over a wide voltage range from −1.4 to 0.2 V, which outperforms pristine VS4. Density functional theory (DFT) calculations showed the proximity of VS4 on CNF allowed V–C bond formation, which resulted in an enhancement of the electronic states near the Fermi level compared to pure VS4. Therefore, the improved capacitance for the VS4@CNF heterostructure is due to the contribution of pseudocapacitance from the CNF, and benefits from the altered VS4 morphology over CNF, which may facilitate electrolyte accessibility. The observed high charge storage capacity and the cycling reversibility with 86% capacity retention after 5000 cycles of the VS4@CNF2x symmetric device is credited to the robustness of the layered VS4@CNF composite material. This study highlights the rational design of 2D materials@1D nanomaterials to provide better interfacial interaction and assist in the self-assembled hierarchical growth of hybrid materials, to satisfy the ever-growing needs in a wide arena of applications. [ABSTRACT FROM AUTHOR]

In this work, thick deposits of pure titanium (Ti), with a thickness of around 15 mm, were additively manufactured using high-pressure cold spraying. Nitrogen was employed as the process gas. Subsequently, the deposits were subjected to hot isostatic pressing (HIP). The HIP-treated Ti deposits were analyzed for their metallurgical and mechanical characteristics with the aim of exploring the viability of using cold spraying for the additive manufacturing of Ti components. Moreover, high-temperature cyclic oxidation testing was also performed on the HIP-treated Ti deposit to understand its stability at high temperatures. SEM/EDS showed a dense structure with marginal porosity for the HIP-treated Ti deposits, without any oxide formation, which was further confirmed via XRD analysis. An average microhardness of 214 HV was measured for the HIP-treated Ti deposits, which is close to that of the commercially available bulk titanium (202 HV). The high-temperature oxidation studies revealed that the cold-sprayed HIP-treated Ti has very good oxidation resistance, which could be attributed to the formation of protective titanium dioxide in its oxide scale. [ABSTRACT FROM AUTHOR]

Hot corrosion is a critical problem in a wide range of high-temperature applications. Ni–20Cr alloy is frequently used in such applications owing to its good hot-corrosion resistance. In the current work, thick Ni–20Cr plates in a thickness range of 6–10 mm were fabricated using cold spray-based additive manufacturing (CSAM). High-pressure cold spraying was used with nitrogen as the propellant gas. Pre- (substrate heating, SH) and post-heat treatments (hot isostatic pressing, HIP) were also performed to comprehend the changes in the deposit properties. The deposits were subjected to microstructural and mechanical characterization to explore the potential of cold spraying for CSAM of Ni–20Cr standalone products. The cold-sprayed plates were successfully developed without any oxide formation. HIP treatment was found to be useful to reduce porosity. The cold-sprayed substrate-heated Ni–20Cr deposits exhibited excellent oxidation resistance at a high temperature of 900 °C. [ABSTRACT FROM AUTHOR]

Micro/nano scale surface modifications of titanium based orthopedic and cardiovascular implants has shown to augment biocompatibility. However, bacterial infection remains a serious concern for implant failure, aggravated by increasing antibiotic resistance and over usage of antibiotics. Bacteria cell adhesion on implant surface leads to colonization and biofilm formation resulting in morbidity and mortality. Hence, there is a need to develop new implant surfaces with high antibacterial properties. Recent developments have shown that superhydrophobic surfaces prevent protein and bacteria cell adhesion. In this study, a thermochemical treatment was used modify the surface properties for high efficacy antibacterial activity on titanium surface. The modification led to a micro‐nano surface topography and upon modification with polyethylene glycol (PEG) and silane the surfaces were superhydrophilic and superhydrophobic, respectively. The modified surfaces were characterized for morphology, wettability, chemistry, corrosion resistance and surface charge. The antibacterial capability was characterized with Staphylococcus aureus and Escherichia coli by evaluating the bacteria cell inhibition, adhesion kinetics, and biofilm formation. The results indicated that the superhydrophobic micro‐nano structured titanium surface reduced bacteria cell adhesion significantly (>90%) and prevented biofilm formation compared to the unmodified titanium surface after 24 h of incubation. [ABSTRACT FROM AUTHOR]

Synthetic superhydrophobic surfaces have drawn significant interest owing to their water-resistant and self-cleaning applications. However, most of the fabrication practices involve complex processes that are unsustainable to withstand large-scale fabrication to transform into standard industrial practice. The desired durability of these surfaces is another crucial challenge that makes the translation of these products difficult. In this paper, we reported the fabrication of superhydrophobic aluminum alloy with a simpler, low-cost, and eco-friendly technique using the hydrothermal treatment. Subsequently, the surface energy of the processed substrate was modulated using a chemical vapor deposition technique. The developed surface shows an extreme water repellency with a contact angle above 160° and a very low contact angle hysteresis and rolling angle (<5°). Surface morphological characterizations showed the formation of nanoscale hierarchical structures which resulted in a stable Cassie state due to the effective entrapment of air and exhibiting self-cleaning ability. The developed surface showed extreme wetting resilience during exposure to a droplet impingement with an impinging velocity of >2 m/s. Further, these superhydrophobic surfaces were exposed to atmospheric weather conditions to check their robustness. During a rain simulator testing, a developed surface showed low contact angle hysteresis (<10°) after enduring multiple cycles. The processed surface also showed significant de-wetting behavior during condensation experiments and chemical resistance under prolonged exposure. Weathering tests performed under outdoor conditions showed an insignificant influence on the de-wettability of the processed sample. The present study highlights the fabrication of superhydrophobic durable metallic surfaces through a facile and green fabrication route for multifunctional applications. [ABSTRACT FROM AUTHOR]

The authors report the development of AlxCoCrFeNi (x = 0.1 to 3) high entropy alloy (HEA) coatings using a simple and straightforward microwave technique. The microstructure of the developed coatings is composed of a cellular structure and diffused interface with the substrate. The microstructure of the HEA coatings varies as a direct function of Al content. An increase in Al fraction shows structural transformation from FCC to BCC along with the evolution of σ and B2 as the major secondary phases. The diffusion of Mo from the substrate enhances the mixing entropy and promotes σ‐phase formation. The HEA coatings show significantly high hardness compared to SS316L substrate steel (227 HV) with a maximum value of 726 HV observed for three‐molar composition. The fracture toughness exhibits an inverse correlation with the Al fraction with the highest value of around 49 MPa m1/2 observed for Al0.1CoCrFeNi coating. The equimolar coating composition shows lowest erosion rates among all the tested samples due to optimum combination of the mechanical properties. The erosion resistance of the equimolar coating is 2 to 5 times higher than steel substrate and around 1.5 times higher than the non‐equimolar counterparts depending upon the impingement angles. [ABSTRACT FROM AUTHOR]

Tribo‐corrosion is an issue of concern for marine and other fluid machinery. High entropy alloys (HEAs) represent a new category of materials possessing exceptional properties. We investigated the erosion‐corrosion behavior of Al0.1CoCrFeNi HEA. For comparison, stainless steel SS316L is also evaluated. Results indicate that despite low hardness and yield strength, HEA exhibits high erosion‐corrosion resistance compared to steel. The HEA also shows high pitting and passive potentials compared to steel. The superior erosion‐corrosion resistance of HEA is due to high corrosion resistance, and work hardenability. The degradation mechanism investigated using SEM show ploughing as the primary material removal mode (MRM) for HEA at an oblique angle compared to micro‐cutting for SS316L steel. At normal impingement, platelet mechanism is observed to be the dominant MRM. [ABSTRACT FROM AUTHOR]

Activation energy and diffusion kinetics are important in modulating the high temperature oxidation behavior of metals. Recently developed multi-principal element alloys, also called high entropy alloys (HEAs), are promising candidate material for high temperature applications. However, the activation energies and diffusion kinetics of HEAs have been limitedly explored. We investigate the diffusional activation energy for oxidation of Al0.1CoCrFeNi HEA. Compared to conventional steels and Ni-based super alloys, the HEA showed a significantly higher diffusion activation energy. This behavior is explained based on low potential energy of the lattice and interstitial sites which effectively trap the atoms, limiting their diffusion. The atomic mean jump frequency for interstitial diffusion of oxygen in the HEA is four-orders of magnitude lower than T22 and T91 steels and seven-orders of magnitude lower compared to pure iron. Al0.1CoCrFeNi HEA showed the lowest oxidation rate compared to conventionally used steels, super-alloys, and coatings. [ABSTRACT FROM AUTHOR]

High temperature mechanics of nanomoulded amorphous metals was investigated byin situnanomechanical testing. Nanopillars of Pd43Cu27Ni10P20metallic glass were synthesized by thermoplastic forming and their stress–strain response was obtained concurrent with direct observation of their deformation behaviour. This allowed the measurement of mechanical behaviour from nanopillars and the corresponding bulk substrate with identical thermal history. A rise in elastic modulus was seen with increase in temperature for both the nanopillars and substrate, which was explained by diffusive rearrangement of atomic-scale viscoelastic units. The results provide fundamental insights into structural rearrangement in metallic glasses. [ABSTRACT FROM PUBLISHER]

Noble-metal-based amorphous alloys show exceptional electrocatalytic activity and durability, and are promising for next generation electrochemical devices for energy conversion and storage. Here, we report on the electro-mechanical behavior of pulsed laser deposited Pt-based metallic glass thin film of composition Pt57.5Cu14.7Ni5.3P22.5. Pulsed laser deposition is ideally suited for the synthesis of thin films with complex compositions since the congruent evaporation process ensures that the composition of the ablation target is replicated in the film being grown. High resolution transmission electron microscopy and X-ray diffraction show that the deposited film is fully amorphous. X-ray photoelectron spectroscopy shows that the constituent elements in the thin film are in their elemental state, forming an isotropic amorphous structure. Nano-indentation determined elastic modulus and hardness values of 52.8 and 2.98 GPa, respectively. In addition, the thin-films exhibited unusually high ductility and low coefficient of friction. The sheet resistance of the as-deposited films was found to be around 76 mΩ sq−1. By current measurement during indentation, we demonstrate current drop during shear band nucleation, which is attributed to increased electron scattering from localized heating. [ABSTRACT FROM AUTHOR]

The atomic distribution in catalytically active metallic glass alloys, Pd43Cu27Ni10P20 and Pt57.5Cu14.7Ni5.3P22.5, was investigated using three-dimensional atom probe microscopy. Atom probe analysis showed uniform distribution of constituent elements for both the starting amorphous alloys, with no phase separation. Both the crystallized alloys showed eutectic microstructure with a very sharp interface (~0.5 nm as determined from atom probe). The atomic distribution in the devitrified state is explained based on the “fragile liquid” behavior for these noble-metal glassy alloys. [ABSTRACT FROM AUTHOR]

The crystallization behavior and viscosity of an in situ metallic glass composite was investigated using a non-contact electrostatic levitation technique. The width of the supercooled liquid region for the amorphous matrix was found to be 74 K, indicating its excellent stability against crystallization. The viscosity data follows the Vogel–Fulcher–Tammann relation, which was used to determine the fragility of the composite melt. The viscosity of the composite is compared to monolithic metallic glasses in the context of “strong-fragile” liquid behavior. [ABSTRACT FROM AUTHOR]

Friction stir processing (FSP) was carried out for AE42 Mg alloy resulting in significant grain refinement and uniform dispersion of fine in situ precipitates. The average grain size was 20 μm for the as-cast AE42 alloy, which was refined to 1.5 μm after FSP. Tensile testing revealed significantly higher modulus and yield strength for the friction stir processed (FSPed) specimen with some improvement in ductility. The fractured surface of the as-cast alloy showed ridges, grooves and cracks indicating brittle failure. In contrast, the fractured surface of FSPed specimen showed fine dimples, characteristic of ductile failure. Nano-indentation was used to analyze the variation of hardness and modulus across the nugget zone of the FSPed specimen. FSPed specimen demonstrated greater strain-hardening tendency compared to the as-cast alloy. Enhancing the mechanical properties of Mg alloys can result in substantial cost savings across a number of industries and have wide economic impact. [ABSTRACT FROM AUTHOR]

Friction stir processing (FSP) of Mg based AE42 alloy was performed under single pass as well as double pass conditions. The evolution of microstructure was investigated using electron back scatter diffraction (EBSD) analysis. EBSD revealed that the grain size and texture varies within the nugget zone of friction stir processed region. The variation of mechanical properties across the nugget region was evaluated using nanoindentation. Hardness and Young's modulus was found to increase along the depth of the friction stir processed specimen. This was attributed to a finer grain structure with increasing depth. The friction stir processed specimen showed higher tendency toward strain hardening compared to as-cast alloy. Understanding microstructure-property relationship paves the way for optimization of FSP conditions and development of advanced functional Mg alloys. [ABSTRACT FROM AUTHOR]

The wettability of different nanotextured metallic glass surfaces is investigated. Wettability is quantified by the sessile drop technique using a distilled water droplet. It is demonstrated that hydrophilic–hydrophobic nature of the metallic glass surface can be controlled through nanotopography. The contact angle was found to increase from 70° for the flat metallic glass surface to 110° for a nanorod patterned surface. The difference in contact angle is explained in terms of the surface topography/roughness measured using atomic force microscopy. [ABSTRACT FROM AUTHOR]

We demonstrate the refinement and uniform distribution of the crystalline dendritic phase by friction stir processing (FSP) of titanium based in situ ductile-phase reinforced metallic glass composite. The average size of the dendrites was reduced by almost a factor of five (from 24 μm to 5 μm) for the highest tool rotational speed of 900 rpm. The large inter-connected dendrites become more fragmented with increased circularity after processing. The changes in thermal characteristics were measured by differential scanning calorimetry. The reduction in crystallization enthalpy after processing suggests partial devitrification due to the high strain plastic deformation. FSP resulted in increased hardness and modulus for both the amorphous matrix and the crystalline phase. This is explained by interaction of shear bands in amorphous matrix with the strain-hardened dendritic phase. Our approach offers a new strategy for microstructural design in metallic glass composites. [ABSTRACT FROM AUTHOR]