查看更多>>摘要：The understanding of the fracture mechanism of amorphous alloys (AAs) is of importance for their engineering applications as advanced structural materials. In this study, a series of micro-tensions of Cu_(45)Zr_(45)Co_(10) AA microwires were conducted under different strain rates ranging from 5 x 10~(-5)s~(-1) to 1 x 10~(-2)s~(-1). It is found that all microwires fracture by shear cracking, but the shear fracture strengths exhibit pronounced rate-dependent uncertainties. Based on both lognormal and Weibull statistical analyses, the studied AA microwires reveal a positive rate-sensitivity of fracture strengths. However, increasing strain rates incurs the decrease in the fracture reliability. We demonstrate that the fracture reliability of AA microwires is dominated by a square root singularity of the characteristic lengths of shear offset on fracture surfaces, which satisfies linear elastic fracture mechanics.
查看更多>>摘要：The removal of low concentration pollutants in water is very important for environmental remediation. Herein, MCr-LDHs/BiOBr (M = Zn, Ni, Cu) heterojunction nanocomposites were fabricated by a facile rapid crystallization method. Visible-light responsive heterojunctions could be formed efficiently at the intimately contacted interface between BiOBr nano-crystallites and LDHs nano-flakes, which showed higher photocatalytic degradation activities of cationic, anionic, and electrically neutral organic pollutants than pristine LDHs and BiOBr. Degradation of 99.5% Rhodamine B, 80% methyl orange, and 97% bisphenol A could be achieved by the composite catalysts under visible-light irradiation in 15 min, 60 min, and 40 min, respectively, and cycling test proved the good reusability of composite catalysts as well. Benefitting from superior adsorption properties for ionic organic pollutants, and effective separation and transition of photogenerated holes and electrons, the MCr-LDH/BiOBr composite catalysts exhibit wide applicability for removal of various organic pollutants in water and have potential application prospects in the future.
查看更多>>摘要：Transition metal sulfides (TMSs) have been widely researched as promising electrode materials for super-capacitors because of their high theoretical capacitance and rich redox reactive sites. In this work, tremella-like core-shell Co_9S_8@NiCo_2S_4 heterogeneous nanosheets were directly grown on Nickel foamed (NF) through the hydrothermal+electrodeposition method to obtain a self-supporting electrode. Benefiting from its unique tremella-like structure, ultra-thin nanosheets, and the positive synergies between Co_9S_8 and NiCo_2S_4, the prepared Co_9S_8@NiCo_2S_4@NF electrode presents a high specific capacity of 513 C g~(-1) (specific capacitance -1026 F g~(-1)) at 1 A g~(-1) with superior rate capability (62.8% capacitance retention rate at 10 A g~(-1)). Furthermore, the fabricated Co_9S_8@NiCo_2S_4@NF//active carbon (AC) hybrid supercapacitor displays a high energy density of 30 Wh kg~(-1) at a power density of 731.8 W kg~(-1) and superior cycling stability. The results prove that the strategy of hydrothermal+electrodeposition is a very effective method for the preparation of energy storage and conversion materials with unique core-shell morphology.
查看更多>>摘要：Luminescence thermometry (LT) is a remote technique of temperature monitoring, which shows immense potential and has become very popular among researchers in recent years. LT can be realized by several different measurement methods, but one of the most recently proposed and least studied relies on a single-band ratiometric (SBR) approach. In the SBR approach, the temperature readout is achieved from a single emission band being photoinduced by two different excitation conditions, i.e. ground (GSA) and excitated (ESA) state absorption. However, the intensity of emission resulting from ESA excitation is dependent on many factors such as host material properties, type and concentration of optically active dopant ions, surface effects, and others, so an in-depth understanding of photophysical processes is essential for the intentional development of novel highly sensitive luminescent thermometer operating on the SBR principle. In these studies, the impact of host and interionic interactions occurring through cross-relaxation on the thermometric properties of a single-band ratiometric thermometer based on nanosized NaYF_4 and NaGdF_4 fluorides doped with Eu~(3+) ions are investigated and discussed. The maximum relative temperature sensitivity was equal S_R= 16.9%/K at 163 K for the NaGdF_4:50%Eu~(3+) nanocrystals and was close to 1%/K over the entire higher temperature range analyzed.
查看更多>>摘要：In this study, 15-5 precipitation hardening (PH) martensitic steel powder was successfully deposited on U75V eutectoid pearlitic steel to form structurally graded material (SGM) using directed energy deposition (DED) technology. Microstructure evolution mechanism and mechanical properties of U75V/15-5PH SGM were investigated systematically. Results show that the microstructural transition zone (MTZ) is formed above the fusion line due to the dilution effect of eutectoid pearlitic steel. The phase composition of MTZ consists of martensite, retained austenite, and carbides, which is distinct from that of directed energy deposited 15-5PH steel. MTZ possesses the highest microhardness owing to the solid solution strengthening and second phases strengthening of carbon elements provided by eutectoid pearlitic substrate. Special intrinsic thermal cycles of DED lead to the formation of heat affected zone (HAZ) below the fusion line, in which the spheroidization phenomenon of lamellar cementite occurs. The spheroidization degree of lamellar cementite in HAZ is exacerbated with increasing distance from the fusion line. Compared with wrought U75V substrate, the lower tensile strength of SGM is mainly attributed to the weak phase boundaries strengthening of granular pearlite at the bottom of HAZ.
查看更多>>摘要：Exploring comwposite nanomaterials with novel and stable nanostructures is of great importance for high performance supercapacitors (SCs). Herein, the nanosheet-like XMoO_4 (X=Ni, Co) were uniformly grown on the carbon submicrofibers (CMFs) by a facile hydrothermal route. The NiMoO_4 @CMFs exhibits higher specific capacitance of 1485.53 F g~(-1) and better cycling stability with 87.6% retention after 3000 cycles at 1 A g~(-1) than that of CoMoO_4 @CMFs (1407.1 F g~(-1) 80.6% retention after 3000 cycles at 1 A g~(-1)). To further improve the electrochemical performance of NiMoO_4 @CMFs, the hollow porous carbon submicrofibers (HPCMFs) were designed and used as a substrate for NiMoO_4. Benefiting from the hollow porous structure, the HPCMFs can provide large specific surface area for electrolyte permeating and supply more ion channels in the charge-discharge process. Therefore, the NiMoO_4 HPCMFs exhibits a high specific capacitance of 1600.0 F g~(-1) at 1 A g~(-1) and good cycling stability of 90.7% retention after 3000 cycles. The all-solid stated symmetric supercapacitors (ASSCs) were directly assembled by using NiMoO_4 @HPCMFs as electrode without any additives, which shows good flexibility and a high energy density of 55.33 Wh kg~(-1) at a power density of 999.89 W kg~(-1). Moreover, five series ASSCs can light 'DHU' logo, indicating potential application prospect in wearable electronics.
查看更多>>摘要：The hot deformation behaviour of Al-Sil2CulMgl alloy foam, Al-Sil2CulMgl alloy-single-wall carbon nanotubes (SWNTs), Al-Sil2CulMgl-cenospheres, and Al-Sil2CulMgl-cenosphere-SWNTs hybrid foams (HFs) were investigated at different test temperatures (25-400 °C) and strain rates (10~(-3)-1 s~(-1)) conditions. It is observed that the energy absorption capacity of all the foams decreased with an increased test temperature (TT) whereas it increased with an increase in strain rate. The hybrid foam in which the cenosphere and SWNTs were added together exhibited the highest plateau stress and energy absorption amongst all investigated foams. The strain rate sensitivity and activation energy for each kind of foam was calculated as a function of temperature and strain rate. The activation energy data tells that the deformation mechanism is dominated by vacancy and dislocation diffusion at TT< 200 °C regardless of the type of foam, strain rate and relative density. On the other hand, the deformation mechanism is dominated by dynamic recovery and recrystallization when the TT increase beyond 200 °C (TT > 200 °C). This study further demonstrates the synergistic effect of cenosphere and SWNTs on enhancing the plateau stress and energy absorption of HFs.
查看更多>>摘要：Additive manufacturing has been vastly applied to fabricate various structures of nickel-titanium (NiTi) shape memory alloys due to its flexibility to create complex structures with minimal defects. However, the microstructure heterogeneity and secondary phase formation are two main problems that impede the further application of NiTi alloys. Although post-heat treatment is usually adopted to improve or manipulate NiTi alloy properties, it cannot realize the spatial control of thermal and/or mechanical properties of NiTi alloys. To overcome the limitations of uniform post-heat treatment, this study proposes an in-situ heat treatment strategy that is integrated into the directed energy deposition of NiTi alloys. The proposed method will potentially lead to new manufacturing capabilities to achieve location-dependent performance or property manipulation. The influences of in-situ heat treatment on the thermal and mechanical properties of printed NiTi structures were investigated. The investigations were carried out in terms of thermal cycling, microstructure evolution, and mechanical properties by 3D finite element simulations and experimental characterizations. A low-power laser beam was adopted to localize the in-situ heat treatment only to the current printed layer, facilitating a reverse peritectic reaction and a transient high solution treatment successively. The proposed in-situ heat treatment on the specimen results in a more obvious phase transformation peak in the differential scanning calorimetry curves, about 50-70% volume reduction for the Ti_2Ni phase, and approximately 35 HV reduction on microhardness.
查看更多>>摘要：The key to synthesis highly efficient MoS_2 based electrocatalyst for hydrogen evolution reaction (HER) is to construct a reasonable composite system structure to improve the stability, reduce the aggregation and improve the intrinsic poor conductivity. In this paper, M0S_2 composite of erbium-based metal-organic framework (noted as Er-MOF/MoS_2) were synthesized by hydrothermal method. The morphology and structure of the synthesized samples were characterized by powder X-ray diffraction (XRD), field emission electron microscopy (FESEM), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), and the electrocatalytic performances were tested by linear sweep voltammograms (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), i-t. On the basis of the experiment, Er-MOF/M0S_2 shows improved conductivity and more exposed active sites, exhibiting excellent HER activity in acidic media, with only 234 mV overpotential to achieve 10 mA cm~(-2), and a Tafel slope of 54.3 mV dec~(-1). This strategy of porous structure of MoS_2 composite rare earth metal organic framework materials provides a novel and effective solution for preparing high performance MoS_2 based electrocatalyst.
查看更多>>摘要：As-explosive welded clad plates usually show poor ductility due to heavily deformed microstructures developed after explosive welding (EXW). In this study, the feasibility of improving mechanical properties of an EXWed Mg-6Al-1Zn-lCa (AZX611)/AI-0.6Mg-0.6Si-0.1Fe (A6005C) (all in wt%) clad plate has been explored by subsequent hot-rolling. Increasing the thickness reduction per pass from 10% to 28% or decreasing the rolling temperature from 430 °C to 250 °C is shown to enhance tensile properties. The joint sheet rolled at 250 °C with a thickness reduction per pass of 28% shows a large fracture elongation of 15%, which is significantly higher than that of the as-EXWed clad plate, 1.2%. Microstructure characterization by means of scanning electron microscope, electron backscatter diffraction and transmission electron microscope reveals that the substantial improvement in ductility is intimately related to a significant reduction of the accumulated strain in AZX611 and A6005C alloy sheets and an elimination of the interface delamination formed during EXW. A certain degree of anisotropic mechanical properties is observed in all sheets regardless of rolling conditions, which can be ascribed to the mechanical anisotropy originated from the AZX611 and A6005C alloy sheets.
NSTL
Elsevier