查看更多>>摘要：The present investigation was an evaluation of the microstructure and mechanical properties in as-cast non-equiatomic medium entropy alloys (MEAs) (AlNi2)70-xCo30Crx (with x = 2.5, 10, 17.5, and 25 at.%), showing dual- or multi-phases structure (near-eutectic microstructure). The majority phase of developed MEAs was FCC (L12) phase and the minority phase was the ordered BCC (B2) phase. The t typical eutectic microstructure was formed in the matrix area of all MEAs and a little dendrite structure was identified in microscopic analysis. The dendrite structure changed from the B2 phase to the L12 phase with an increase in Cr contents. When the composition of Cr contents was 10% that consists of a fully eutectic structure, it showed the highest yield strength of 865.7 MPa together with excellent plastic strain. Interestingly, it was found that abnormal deformation behaviors were also observed in the stress-stain curve exhibiting two times of yielding phenomenon typically called “double-yielding”. Through TEM analysis, it was confirmed that the observed double-yielding phenomenon is related to the phase transformation from the B2 phase which constitutes the eutectic lamellar to L10 phases during compressive loading. In this study, we discussed detailed deformation mechanisms that can induce excellent mechanical properties of eutectic MEAs.
查看更多>>摘要：Metal halide perovskites have been an attractive optoelectronic material for light-emitting diodes (LEDs) and display applications as well as photovoltaic devices. However, poor device performance and operation stability still impede their development and application. This paper reports a facile surface modification method to enhance the performance of CsPbBr3 thin film-based LEDs using CsF with various molar contents. Structural and chemical investigations showed that the CsF treatment removes the surface pinhole defects and fluorinates the CsPbBr3 surface simultaneously, which resulted in the enhanced photoluminescence intensity compared to the pristine one. The CsF treatment enhanced the LED performance by increasing the electroluminescence intensity while mitigating the saturation behavior, even under high applied bias. These outcomes were attributed to the advantageous roles of the CsF treatment, i.e., removal of surface pinhole defects, passivation of surface non-radiative defects, and the formation of an electron blocking layer.
查看更多>>摘要：One-dimensional Ni porous nanofibers (Ni PNFs) were prepared through a facile electrospinning followed by hydrogen reduction process, and their electromagnetic characteristics and microwave absorbing properties were investigated. Benefiting from the unique microstructure, three-dimensional conductive network and multiple attenuation forms, Ni PNFs exhibit remarkably increased dielectric loss capacity and improved impedance matching level relative to Ni nanoparticles. Consequently, Ni PNFs offer a significantly enhanced microwave absorption property with a minimum reflection loss (RL) of ?40.4 dB at a relatively low filling ratio of 30 wt% and an effective absorption bandwidth (RL<?10 dB) of 4.6 GHz (8?12.6 GHz). Our results demonstrate that the microstructure and morphology of materials have considerable influence on their electromagnetic performances and the as-obtained Ni PNFs can be a promising candidate for lightweight and high-efficiency microwave absorption or electromagnetic shielding.
查看更多>>摘要：The Sn addition MnBi bulk magnets with high density and superior coercivity (Hc) were prepared by hot compaction. It was found that the added Sn was dispersed between the MnBi particles as an intergranular phase. The appropriate intergranular phase content could be beneficial in improving the Hc due to the strong magnetic isolation effects. The Hc of the MnBi/Sn bulk magnet was increased from 8.6 kOe to 11.5 kOe as the Sn addition contents were increased in the range of 0 wt.% to 5 wt.%. A relatively high squareness (Mr/Ms) of 0.91 was obtained for the 1 wt.% Sn addition Mn56Bi44 bulk magnet exhibiting the maximum energy product (BH)max of 7.8 MGOe with high Hc of 10 kOe at room temperature.
查看更多>>摘要：Carbon-based nanomaterials are widely employed for microwave absorption. However, reasonable methods to enhance microwave absorption capacity remain worth exploring. Herein, carbon nanofibers (CNFs) modified by silicon carbide and metal silicide (SiC/Fe3Si/C) were fabricated through electrospinning and high-temperature pyrolysis processes, and their phase composition, micro-morphology, micro-structure, and magnetic characteristics evaluated. The composite nanofibers (SiC/Fe3Si/CNFs) exhibited excellent microwave absorption, with minimum reflection loss (RLmin) values of ?41.6 dB at 12.8 GHz and a matching thickness of 4.5 mm. Further, the maximum effective absorption bandwidth (EAB, RL<?10 dB) of the as-synthesized sample is 11.5 GHz with a matching thickness of 5 mm. These novel carbide and intermetallic compounds loaded CNFs are remarkable candidates for lightweight, tunable, and efficient microwave absorbers.
查看更多>>摘要：Sparking plasma sintering (SPS) technique has the characteristics of rapid heating and cooling rate, high mass density, and grain activation sintering. Therefore, it may be used to improve the grain connection, refine the grains, and enhance the superconducting current-carrying capacity of MgB2. In this paper, the MgB2 wire prepared by the in-situ method is rapidly treated by the SPS method, and the effects of different SPS sintering conditions on the phase formation, microstructure characteristics and superconductivity of the MgB2 material are studied, and compared with the MgB2 prepared by conventional sintering and the ex-situ SPS method. It was found that the SPS-treated samples were in a rapidly changing non-equilibrium state during the entire sintering process, so there are existing both flake particles and nanoparticles in the samples, which significantly improves the connection of the grains and refine the grains, resulting in significantly improved superconducting performance for MgB2. The critical current density Jc of SPS-treated sample at 850 ℃ reached 1354 A/cm2 @ (10 K, 5 T) and 1615 A/cm2 @ (20 K, 3 T), which were 3.7 times and 2.6 times that of conventional sintering sample. Our research shows that SPS is an effective method to improve the superconductivity of in-situ MgB2 wire.
查看更多>>摘要：Selective phase corrosion (SPC) is one of the most serious failure modes for as cast NiAl bronze (NAB) alloy. In this paper, the electrical properties of corrosion protective film of each phase in the alloy was investigated using atomic force microscopy (AFM) electrical modes, and its effect on the SPC behavior in different (pH=2, 3.5, 4.2 and 7) 3.5% NaCl salt solution was also scientifically studied. The results show that in neutral solution, the protective films of κ and β′ phases exhibit higher Volta potential and lower-conductivity compared with α phase. But after long time immersion, the film of β′ phase is easy to form micro-cracks, resulting in its severe corrosion. At pH value of 3.5, no SPC occurs, leading to the best corrosion resistance of the alloy. Below and above 3.5, the alloy exhibits completely different SPC behavior. Below 3.5, the protective film was destroyed, and the SPC mainly depends on the Volta potential of each phase. Above 3.5, due to the different electrical properties of protective film, the adjacent α phase around the κ phases is preferentially corroded, which eventually leads to the separation of κⅱ and κⅳ phase and α phase corrosion in α + κⅲ eutectic structure.
查看更多>>摘要：In this paper, Li-doped ZnO nanowires were grown on flexible carbon fiber substrates by hydrothermal route to create hybrid antibacterial structures. We have reported the synthesis, characterization and antibacterial activity of these hybrid structures which are made up of ZnO nanowires incorporated with various amounts of Li (0.3%, 0.5%, 1%, 3%, and 5%). Structural, morphological, optical, and elemental properties of the samples were scrutinized by using X-ray diffractometry (XRD), photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), respectively. The antibacterial effect of the hybrid structures against Escherichia coli and Staphylococcus aureus was tested by colony counting method. From the results, the antibacterial effect of Li-doped ZnO/CF against both E. coli and S. aureus was observed to considerably high in all samples. It was also seen that the Li addition significantly improves the antibacterial effect of ZnO nanowires. Doping ZnO with 3% Li resulted in best antibacterial efficiency on both E. coli (99.3% inhibition) and S. aureus (98.7% inhibition) among all samples.
查看更多>>摘要：Direct methanol fuel cells have attracted extensive research interest because of their relatively high energy density and portability. It is important to rationally design the composition and surface atomic structure by efficient synthesis protocols to boost cell efficiency. In this study, we employed cohesive pulsed laser irradiation and ultrasonochemical techniques to synthesize and tune the molar ratio of an Au–Pd alloy for the methanol oxidation reaction (MOR). The effective implementation of extremely rapid photoinduced reduction and reaction conditions resulted in the formation of well-dispersed and homogenous nanospheres of the Au–Pd alloy with uniform particle size. Moreover, the composition-tuned Au–Pd alloy exhibited an improved electrocatalytic activity, which might be due to its improved electrical conductivity and higher CO tolerance. The alloy achieved relatively high mass and specific activities of 0.50 A/mgPd and 1.36 mA/cmPd2, respectively. Additionally, we studied the effect of the Au–Pd composition on the MOR activity and analyzed the reaction kinetics in depth. This work provides the foundation for implementing a laser-based technique to synthesize Pd-based alloy electrocatalysts for MOR application.
查看更多>>摘要：The strength and deformation behavior of the aluminium alloy AA7075 was crucial information for engineering and manufacturing design. Tensile tests were performed in a temperature range of 25–300 °C on the aluminium alloy AA7075-T651. Flow curves at different temperatures were shown. The work hardening behavior was analyzed using the Kocks-Mecking and Crussard-Jaoul models. Flow curves in hardening regimes were predicted using constitutive models, i.e., Hollomon, Ludwigson, Ludwik, Swift, and Voce. At high temperatures involved with softening phenomenon, Voce model combined with linear softening or Voce softening were used to predict flow stresses. A novel approach, Voce hardening and softening models combined with the piecewise nonlinear regression technique, was introduced. It was found that the plastic deformation of aluminium alloy AA7075 was dominated by only one mechanism indicated by one slope of stage III in the K-M plot. The hardening regime was found at room and elevated temperatures and could be predicted reasonably using all constitutive equations. At elevated temperatures, the novel approach predicted flow stresses with great accuracy.
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Elsevier