查看更多>>摘要：The liquid-solid phase transitions and solidified microstructures of highly undercooled Fe-Zr eutectic melts were investigated by the drop tube technique. The quantitative relationships among droplet diameter (D), undercooling (ΔT) and cooling rate (R_c) were calculated for three types of eutectic alloys (Fe-9.8 at. % Zr, Fe-6 at. % Zr and Fe-16 at. % Zr alloys). Furthermore, the evolutions of solidified microstructure with droplet diameter were studied. The results show that the eutectic microstructure for Fe-9.8 at. % Zr droplet transforms from regularly lamellar shape to anomalous shape as the diameter reduces. The α-Fe dendrite in Fe-6 at. % Zr droplet transforms from coarse dendrite to refined dendrite with the decrease of droplet diameter, while the Fe_2Zr dendrite in Fe-16 at. % Zr droplet transforms from faceted dendrite to non-faceted grain. Besides, a remarkable solid solubility extension was found in both the α-Fe dendrites of Fe-6 at. % Zr alloy and the Fe_2Zr dendrites of Fe-16 at. % Zr alloy. The solid solubility of the a-Fe dendrite increases from 3 at. % to 5.6 at. % when the droplet diameter reduces from 1069 to 212 um, while it decreases from 31 to 22 at. % in the Fe_2Zr dendrite as the diameter reduces from 991 to 228 um. The microstructural morphology and solid solubility are directly related to the nano-hardness and Young's elastic modulus of alloys. The nano-mechanical properties of the eutectic gradually increase with the refinement of the layers, and gradually decrease as the irregularity of the anomalous eutectic increases. With the reduction of droplet diameter, the nano-hardness rises and Young's elastic modulus continuously diminishes for the a-Fe dendrite due to the increase in the solute content of Zr, while these two mechanical properties gradually decrease for the Fe_2Zr dendrite because of the reduction in the solute content of Zr.
查看更多>>摘要：Transition metal sulfides exhibit great potential in the application of sodium ion battery anode materials because of their unique properties and high theoretical capacity. Nevertheless, their inferior rate and cycling performances impede the commercialization process. Pseudocapacitance is a significant sodium ion storage behavior to enhance reaction kinetics, which is beneficial to the improvement of electrochemical performances. Herein, an anode material possessing heterojunction structure has been constructed through decorating SnS_2 nanoparticles on the surface of MoS_2@rGO (SnS_2@MoS_2@rGO), displaying a high reversible capacity of 237 mAh g~(-1) at 3.2 A g~(-1) and 167 mAh g~(-1) at 6.4 A g~(-1) after 140 cycles. The good electrochemical performances of SnS_2@MoS_2@rGO electrode can be ascribed to the enlarged surface areas and fast sodium ion transport channel resulting from the heterojunction structure. In addition, the sodium ion full cell consists of SnS_2@MoS_2@rGO anode and Na_3V_2(PO_4)_3@C cathode can even exhibit ideal specific capacity (33 mAh g~(-1) at 20 C (1 C = 117 mA g~(-1))), showing potential application prospects.
查看更多>>摘要：The microstructure changes and mechanical properties of dual-phase U-2 Nb alloy subjected to shot peening treatment (SPT) were investigated. SPT induced severe plastic deformation in the U-2 Nb alloy surface, and a gradient nanostructure was formed on the surface with the grain size ranging from nanocrystallization structure to coarse grains from the surface to the matrix. The results showed that both the α phase with an orthorhombic crystal structure and the y phase with a body-centered cubic structure in the surface layer of the U-2 Nb alloy were refined to nanocrystals with an average nanocrystallization structure size of 63 nm. Due to the concentration of stress at the α/γ interface and grain size effect, the refinement of the α phase matrix occurred before y phase. Furthermore, dislocation slipping caused by deformation, rather than deformation twinning, played a key role in the grain refinement of U-2 Nb alloy. Microhardness and tensile tests showed that both surface microhardness and tensile strength were improved after SPT.
查看更多>>摘要：Nonlinear-optical (NLO) metal aluminium phosphate crystal materials with deep-ultraviolet (DUV) transparent ability remain greatly unexplored. Herein, mixed alkali/alkaline-earth metal aluminium phosphate DUV NLO crystal Na_2Ca_(17)Al_2(PO_4)_(14) was successfully synthesized through the high-temperature molten technology. Na_2Ca_(17)Al_2(PO_4)_(14) features a 3D Ca-cluster-constructed framework by the stacking of Ca_6O_(36) and (Ca/Na)_3O_(19) clusters, which is filled by isolated A1(PO_4)_6 clusters and isolated PO_4 tetrahedra. Na_2Ca_(17)Al_2(PO_4)_(14) exhibits a short UV absorption edge below 190 nm, phase-matching behavior with strong NLO effect of 0.9 × KDP, high thermal stability. First-principles calculations indicate that the optical properties of Na_2Ca_(17)Al_2(PO_4)_(14) derive primarily from the Ca-O groups, rather than Al-O and P-O traditional groups. The work may further promote the exploration of new DUV NLO aluminium phosphate crystal materials.
查看更多>>摘要：We prepared a novel three dimensional (3-D) 3d-4f MOF (named as CeCu-MOF; C_(10)H_(10)CeCu_2N_4O_(12)) which exhibits triclinic symmetry P-1 space group, and applied it to the study of electrode materials in organic system and aqueous solution system respectively. In order to overcome the shortcomings of poor electrical conductivity of MOF, we prepared several plant-charcoal materials with discarded grapefruit peel by different carbonization methods. The best electrochemical performance is selected for detailed study. In this paper, different amounts of plant-charcoal and MOF were used as electrode materials for supercapacitors and lithium-ion batteries, and their electrochemical properties were investigated. The results showed that the addition of plant-charcoal did help to improve the electrochemical performance compared with the single-phase MOF.
查看更多>>摘要：In this work, a novel CoMn_2O_4@CoMn_2S_4 core-shell nanocluster@nanosheet was successfully grown onto Ni foam via a hydrothermal reaction, which omitted the addition of a binder and conductive additive and the need for a complicated electrode preparation process. CoMn_2S_4 nanosheets as "shells" were found to be uniformly distributed on the surface of CoMn_2O_4 nanoclusters as "cores" to form a typical core-shell structure. These structures possess a high specific surface area and abundant active sites, which not only shorten the transmission path for electrons and ions, but also prevent collapse of the structure, thus improving its cycling stability. The specific capacity of CoMn_2O_4@CoMn_2S_4 is 1542.0 C g~(-1) at a current density of 1 A g~(-1) which is 3.1 times higher than that obtained for CoMn_2O_4. Moreover, CoMn_2O_4@CoMn_2S_4 shows excellent electrochemical cycling performance, and the specific capacity retention rate for CoMn_2O_4@CoMn_2S_4reaches 95.81% after 5000 cycles at a current density of 20 A g~(-1). The specific energy of the CoMn_2O_4@CoMn_2S_4 reaches 44.30 Wh kg~(-1) at a specific power of 774.98 W kg~(-1). Therefore, the CoMn_2O_4@CoMn_2S_4//AC device shows excellent practical application capability.
查看更多>>摘要：Fabricating Ti_3C_2T_x Mxene based composite with good control of size, morphology and facet for the high-efficiency photocatalytic application is of great potential and highly challenging. In this work, Ti_3C_2-TiO_2 composite are prepared by a simple two-phase assembling method from the Ti_3C_2 Mxene dispersion modified with tetraethyl hydroxyl ammonium (TEHA) and rhombic-shaped TiO_2 nanoparticles with exposed {101} facets. The Ti_3C_2 Mxene acts as a good support to anchor TiO_2 nanoparticles of 15 nm with good facet control. A significantly enhanced photocatalytic hydrogen evolution activity is acquired by the Ti_3C_2-TiO_2 composites. The highest H_2 production rate of 390.92 μmol h~(-1) is gained by the Ti_3C_2-TiO_2 composites with the Ti_3C_2 weight percentage of 6.7%, which is 2.1 times that of pristine TiO_2. The excellent photocatalytic activity can be attributed to the extended light absorption, the boost charge separation efficiency and exposed {101} facets in the TiO_2 nanoparticles. This work provides a new strategy to prepare high quality MXene Ti_3C_2-TiO_2 hybrids with good photocatalytic properties, which could be widely applied to produce other MXene-based composites with excellent properties.
查看更多>>摘要：Poor tribocorrosion resistance of Ti and its alloys remains as a concern for load-bearing biomedical implants. Despite being an effective method to improve tribocorrosion resistance, titanium matrix composites (TMCs) have yet to be used in this type of applications. In-situ TiB (titanium boride) and TiC (titanium carbide) reinforcement phases have been considered as one of the best options to produce TMCs once these phases present high compatibility and strong interfacial bonding with Ti. Although the effect of these phases on the mechanical properties of Ti has been thoroughly researched in the last years, their effect on corrosion, tribocorrosion and biocompatibility of Ti is yet to be fully understood. In this work, in-situ Ti-TiB-TiC_x composites obtained by reactive hot pressing showed identical corrosion response compared to the unreinforced Ti but displayed improved tribocorrosion behaviour. Under 0.5 N load, composites presented as average a reduction of 51% in wear volume loss and under 10 N the reduction was up to 93%. Early biological tests showed promising results, as composites were biocompatible and induced osteoblasts spreading and possibly proliferation most probably due to composite chemistry and surface hardness.
查看更多>>摘要：We study the effect of laser shock peening (LSP) without protective coating on the surface mechanical property of NiTi alloy. The Vickers microhardness and wear resistance are measured to determine the mechanical property of NiTi samples treated with different LSP parameters (3 J with 10 ns and 5 J with 20 ns). From the electron backscatter diffraction (EBSD) analysis, it can be found that the laser shock peening does not induce obvious grain refinement in the surface region of NiTi alloy. Both compressive and tensile residual stress in the top layer are determined using the hole drilling method. The results show that the LSP treatment without a protective coating increases the roughness and enhances the surface mechanical properties of NiTi alloy.
查看更多>>摘要：Rotary swaging (RS), as a widely used industrial method for severe plastic deformation (SPD), is a near net forming process which uses high-speed pulse hammer of multi-hammer to process solid shaft parts or hollow variable cross-section forgings. Initially RS is mainly used to manufacture difficult-to-deform metals with poor plasticity (such as W and Mg alloys, etc.). Recently, because RS process can enable large hydrostatic stresses and facilitate the accumulation of large strain, it is also allowing for high-throughput mass production of different metals with enhanced mechanical properties. This paper first introduces the RS working principle and unique characteristics, then systematically summarized the microstructural characteristics (grain size, texture, etc.), mechanical properties (such as strength, ductility, etc.), physical and chemical properties of various ultrafine grained metals prepared by RS, finally compares the advantages and disadvantages of swaging with other deformation methods, and looks forward to the future development and application fields of rotary swaging.
NSTL
Elsevier