查看更多>>摘要：? 2022 Elsevier B.V.In this study, binary transition metal oxide Mn2V2O7 nanoplates and nanosheet-based hierarchical microstructures were prepared by changing the V/Mn molar ratio in the initial reactants using the solvothermal method. As the anode materials for lithium-ion batteries, the electrochemical properties of both Mn2V2O7 are investigated. After 300 cycles, a discharge capacity of 1014.3 mA h g?1 for Mn2V2O7 nanoplates and 1096.0 mA h g?1 for Mn2V2O7 nanosheet-based hierarchical microstructures can be maintained at the current density of 0.5 A g?1. The nano-sheets structures shorten the transmission paths of ions and electrons, while the synergistic effect occurred between manganese and vanadium elements also enhance the electrochemical activity. Therefore, the manganese vanadium oxide materials prepared in this study exhibit great prospects for application in energy storage devices.
查看更多>>摘要：? 2022 Elsevier B.V.The growing demand for wearable electronics boosts researches on flexible fibrous energy storage devices, such as fibrous Zn-MnO2 battery. One bottleneck for the capacity of fibrous MnO2 electrode, especially at high discharge rate, is the inefficient interfacial charge transfer between nano particles within mechanical-mixed MnO2 aggregates. Herein, nano γ-MnO2 has been in-situ grafted on nano carbon branches via a mild interfacial oxidation reaction using KMnO4-doped MnO2 sol precursor, to form nano composites of MnO2@ hierarchical carbon networks. The grafting reaction selectively takes place at defective sites with a mixed bonding state on the surface of the carbon branches, during which a rapid δ-to-γ crystal transformation is largely boosted, instead of traditional slow δ-to-α crystal transformation. An efficient fibrous MnO2 electrode based on the composites of MnO2@ hierarchical carbon networks is successfully applied to fibrous Zn-MnO2 battery, by giving a 2.5 times of capacitance promotion and a better charging-discharging cycling stability.
查看更多>>摘要：? 2022 Elsevier B.V.Multipass friction stir processing of Fe based metallic glass ribbons interspersed between Cu plates was performed. From the first pass, the process entailed on the one hand the decrease of the Cu mean grain size in the nugget by a factor of about 5 and on the other hand the fracture, the refinement and the partial crystallization of the amorphous reinforcement. Cu diffusion also led to marked Cu enrichments in the Fe based metallic glass whose mean Cu content reached 2.7 at%. Beside the metallic glass based reinforcements, some nanometric polycrystalline copper oxides were formed and dispersed within the nugget. The nugget also experienced dynamic recovery and dynamic recrystallization which was in particular favored by the accumulation of dislocations around the reinforcements. Finally, the greater number of passes, the harder the nugget becomes.
查看更多>>摘要：? 2022 Elsevier B.V.This study investigated the microstructure and cracking mechanism of a matrix high-speed steel fabricated by direct energy deposition. The combined effect of rapid solidification and chemical composition on microstructure and cracking mechanism during deposition were investigated. Excessive solute segregation into inter-dendritic regions due to rapid solidification caused formation of retained austenite in the inter-dendritic region and formation of α'-martensite in the dendritic region. The excess solute segregation decreased equilibrium solidification temperature and caused formation of low-melting eutectic carbides in the inter-dendritic region. These carbides increased hot-cracking susceptibility, and caused solidification cracking and liquation cracking in the inter-dendritic region. In contrast, tensile residual stress in deposited layers may have caused cold cracking in α'-martensite near the hot crack tips. Cold cracks contributed to growth of macroscopic longitudinal cracks throughout the specimen by bridging the hot cracks formed during solidification or reheating.
查看更多>>摘要：? 2022 Elsevier B.V.The present study combines density functional theory (DFT) based calculations and experimental techniques to investigate the formation of equiatomic quaternary “low-activation" high entropy alloys (HEAs) for nuclear fission/fusion applications. DFT based techniques are adopted to screen the formation of possible single-phase ternary and quaternary alloys in chemical space consisting of the low-activation elements (Ti, V, Cr, Mn, Fe, Ta and W). The results indicate that TaTiVW and CrFeMnV can be formed in a single body centred cubic phase (BCC). Based on the DFT based screening, HEAs are fabricated by a vacuum arc melting process. Further characterisation by X-ray diffraction, energy dispersive X-Ray analysis, X-ray fluorescence and scanning electron microscopy confirms the formation of TaTiVW in a BCC single phase. Microstructures of CrTiVW and CrTaVW in as-cast conditions, consist of two BCC phases with very similar lattice parameters. CrTaTiW and CrTaTiV showed evidence of C15 Laves formation comprising of TaCr2 and TiV2, respectively.
查看更多>>摘要：? 2022 Elsevier B.V.Reducing the oxygen adsorption energy barrier is vital to accelerate the oxygen reduction reaction (ORR). Herein, we report a mesoporous cake-like structured Zn-N/Cu-N electrocatalyst (ZnCu-N-C) with robust electrocatalytic performance and exceptional durability in 0.1 M KOH solution. The mesoporous cake-like structure is promising to expose more active sites. Extended X-ray absorption fine spectroscopy and X-ray photoelectron spectroscopy confirmed the existence of M-Nx (M = Zn, Cu). More importantly, the density functional theory (DFT) calculations corroborate that the Zn-N/Cu-N dual active center can reduce the oxygen adsorption energy barrier. Therefore, the optimized ZnCu-N-C electrocatalyst is ahead of commercial Pt/C (20 wt%) in all aspects. Moreover, the ZnCu-N-C-based Zn–air batteries exhibit outstanding long-term stability of 240 cycles, a large power density of 156.2 mW cm?2, and a high specific capacity of 732.7 mA h g?1. This work may provide new guidance for the rational design of cathode catalysts in Zn-air batteries.
查看更多>>摘要：? 2022 Elsevier B.V.Inconel group of alloys, particularly IN 625 and IN 718 are the most widely recognized commercially available Ni-based superalloys employed for high temperature applications. These superalloys are known to retain their extraordinarily high strength at elevated temperatures either by solid solution or precipitation strengthening mechanisms. Consequently, they find crucial applications in the field of aerospace, automobile, and energy industries involving higher temperatures. Recently, attempts are being made to fabricate and repair the complicated superalloy components using metal additive manufacturing techniques. The ability of the additive manufacturing process to produce intricate geometry parts with greater dimensional accuracy as compared to various conventional techniques appear to be beneficial and cost-effective. However, this unique manufacturing method influences the microstructural evolution and thereby affects the performance of the IN 625 and IN 718 alloys significantly. Considering various research efforts in this direction, this article pursues a thorough review and presents a wide overview of the microstructure and mechanical properties correlation for these two additively manufactured Ni-based superalloys.
查看更多>>摘要：? 2022 Elsevier B.V.To explore an efficient way of modifying carbon nanomaterials to improve the interfacial bonding with the Cu matrix, the interaction between Cu and pristine graphene, single- and double-vacant defect graphene, and nitrogen-doped graphene was systematically investigated by density functional theory (DFT) calculations. The electronic structure, including Bader charge and charge density differences, reveals that the existence of vacancies and nitrogen doping are beneficial for the transfer of electrons at the interface, mainly due to the enhanced binding energy and their intense interaction with Cu atomic orbitals. Pyridine-N and pyrrole-N are more capable of coupling with the interfacial Cu atoms, suggests a vital role of nitrogen doping in the improvement of the mechanical and electrical properties of graphene/Cu composites. To validate our computational prediction, heat-treated carbon polymer dot (CPD), which can be regarded as nitrogen-rich graphene, were employed to prepare bulk CPD/Cu composites. The mechanical performance was significantly better than that of the pure Cu matrix, proves that nitrogen doping could effectively improve C/Cu interface bonding. This research provided a theoretical and experimental basis for the preparation of advanced Cu matrix composites.
查看更多>>摘要：? 2022 Elsevier B.V.In this paper, we report on a new compound in the SrO-TiO2-B2O3 system. For the first time, the compound was synthesized by crystallization of glass tapes (GTs) obtained from a melt of 2SrO-2TiO2-B2O3. The crystallization was performed at 670 °C for 96 h. X-ray studies showed that the formed new phase belongs to the hexagonal system. The lattice parameters were calculated as well. It was suggested to attribute the new material to stoichiometric compound Sr3Ti3O6(BO3)2. The dielectric constant, tangent loss, ac and dc conductivities of the material were found to be almost constant in a wide range of temperatures. Investigation of varistor properties showed that the current-voltage nonlinearity coefficient is 2.05. The measurement of the hysteresis loop confirms the ferroelectricity of the material. It is found that the second-harmonic generation intensity of the new material exceeds that of KDP (by a factor of 3.2 for particles in the size range of 100 ÷ 150 μm).
查看更多>>摘要：? 2022 Elsevier B.V.The influences of Sc/Sm microalloying on microstructure, mechanical property, bio-corrosion behavior and biocompatibility of the as-cast Mg-2Zn-0.3Ca alloy have been investigated in the study. The results demonstrate that Sc microalloying obviously refines the grain of the Mg-2Zn-0.3Ca alloy, leading to the improvement of yield strength (82 MPa). While the coarse and discontinuous eutectic phases (α-Mg＋Ca2Mg6Zn3) accelerate the galvanic corrosion near the grain boundary. Sm microalloying promotes the formation of finely dispersed particles (Ca2Mg6Zn3-Sm) of the Mg-2Zn-0.3Ca alloy, reducing the electrode potential difference of the second phase and matrix. The Mg-2Zn-0.3Ca-0.4Sm alloy has the most moderate corrosion and compact protective layer in the three alloys, exhibiting excellent corrosion resistance (Pw = 1.26 mm·y?1) in vitro. The Mg-2Zn-0.3Ca-0.4Sc/Sm alloys are non-cytotoxic and promote cell proliferation.
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