查看更多>>摘要：? 2022 Elsevier B.V.High pressure torsion of alternating foils of elemental Al and Ni is used for the production of highly deformed and highly reactive nanostructured Al/Ni multilayers. A continuous grain refinement of the microstructure from the center to the edge of the as-processed disc from approximately 25 μm down to 20 nm is observed. Using a combination of laboratory and synchrotron techniques the formation of a few Al3Ni nanocrystallites inside Al layers is confirmed in the as-processed multilayered material at high shear strain. Thermodynamic calculations at room temperature of heats of mixing and enthalpy values of phase formation for Al3Ni agree with the experimental observations. Post-processing annealing was performed using in situ TEM and calorimetry. The first phase that forms during the solid state multilayer combustion is confirmed to be Al3Ni followed by Al3Ni2, NiAl and Al2Ni3. High-temperature chip-calorimetry revealed that the onset of reaction is characterized by an activation energy of 1.4 eV (135 kJ/mol-at) and a total heat of reaction of ? 39.0 kJ/mol-at. The latter confirms the self-propagating high-temperature synthesis mechanism of reaction of the as-processed multilayered material.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, the effect of temperature on the morphology, crystal structure, chemical composition, roughness, wettability, Vickers microhardness, and corrosion resistance of thermally oxidized Ti-15Zr-xMo (x = 0, 5, 10, and 15 wt%) samples were evaluated. Thermal oxidation treatments were performed in air, at temperatures between 773 K and 1173 K, for 21.6 ks. Oxide layers were composed preferentially by Ti, with traces of Zr, in TiO2 and ZrO2. The temperature and bulk chemical composition influenced the phase composition, showing formation of different fractions of TiO2 (anatase and rutile) together small amounts of tetragonal and monoclinic ZrO2. The morphology showed the presence of a smooth inner layer with some oxide precipitates in the outer layer, with thickness ranging from 1 μm to more than 100 μm. Roughness and contact angle values changed according to the growth of precipitates in the oxide layers. Vickers microhardness exhibited a sharp increase with the growth of the oxide layers, remaining higher than that for bulk samples. The results indicated that a favorable combination of surface properties could be achieved when optimizing the thermal oxidation treatment, which could assist in broadening the biomedical applications of the Ti-15Zr-Mo based alloys.Ti-15Zr-15Mo alloy thermally oxidized at 973 K exhibited enhanced corrosion resistance, and emerged as the best candidate for use as orthopedical implants.
查看更多>>摘要：? 2022 Elsevier B.V.Lithium-oxygen batteries (LOBs) are emerging as one of the most powerful candidates for the next-generation green energy-storage devices due to their high theoretical energy density. However, the high polarization and poor cycling stability have hampered their practical applications that heavily depend on the dual-functional cathodes with abundant highly active sites to promote the mass/electron transfer for efficient oxygen reduction and evolution. Herein, a space-confined pyrolysis strategy is proposed by coating a Co-based metal-organic framework composite precursor (ZIF-8 @ZIF-67) with an inorganic SiO2 layer, which efficiently inhibits the precursor loss and nanostructure collapse during the high-temperature carbonization and yields a high-performance carbon nanotube-wrapped Co3O4 electrocatalyst. Thereinto, the Co within the precursor can act as the self-catalyst for the growth of abundant carbon nanotubes, which not only generates more catalytic sites but also improves the electronic conductivity. Systematic investigations reveal that the resultant Co3O4 wrapped with carbon nanotubes (Co3O4/CNTs) possesses significantly improved bifunctional oxygen reduction and evolution activity when compared with the Co3O4 counterpart derived from the traditional direct pyrolysis, which is benefited from the large content of active sites and strong mass/electron transfer capabilities to allow the exceptional rate performance and cycling stability of LOBs. The space-confined pyrolysis strategy described herein may help to exploit the highly efficient electrocatalysts.
查看更多>>摘要：? 2022 Elsevier B.V.Submicron-sized single crystal Li1.2Mn0.54Ni0.13Co0.13O2 was prepared to enhance the structural stability and lithium ion migration rate of Li-rich cathode materials. The preparation process of single crystal particles was beneficial for materials with good layered structures and low cation mixing degrees. Due to the single crystal morphology of the materials, the particles remained intact without cracks after cycling, which reduced side reactions between the cathode material and electrolyte, thus preventing the structural phase transformation. The preparation of submicron-sized single crystal particles provides a new strategy to improve the electrochemical properties of Li-rich cathode materials.
查看更多>>摘要：? 2022 Elsevier B.V.We report on an efficient and practical conducting mode built up by ternary conductive networks for boosting the rate performance of LiFePO4 (LFP) cathodes in lithium-ion batteries (LIBs). The influence on the electrical conductivity, rate capability and continuous ion channels of the resulting electrode are investigated. Carbon nanotubes (CNTs) with long-range electronic conduction are ultimately individually dispersed (mono-dispersed) into an electrode slurry, which connects the short-range conductive regions formed by graphene sheets. Importantly, CNTs provide more open channels for electron and ion transportation, than the blocking function of graphene sheets. Local graphene regions are herein bridged by mono-dispersed long CNTs to construct an efficient conductive network, enabling the composite to have improved fast electron/ion open channels. An efficient and practical conducting mode of “plane-to-line-to-point” is demonstrated to construct both short-/long-range electronic conduction and more open ion channels, while further contributing to conductive points all over the surface area of the LiFePO4 cathode.
查看更多>>摘要：? 2022 Elsevier B.V.In this paper, the tensile behavior and deformation mechanism of two typical bimodal microstructures in Ti6242S alloy were investigated through the in-situ scanning electron microscope (SEM) test and electron backscatter diffraction (EBSD). The results showed that the two microstructures presented different mechanical properties due to the different microscopic slip and fracture behaviors. In the homogeneous microstructure (with homogeneous crystallographic orientation), most of the slip traces were restricted within the grains because the slip transmissions between neighboring grains were blocked. The slip deformation was relatively homogeneous. Therefore, the fracture mechanism was micro-void accumulation fracture. In the inhomogeneous microstructure (with many microtextured regions), there existed many long slip traces directly passing through the microtextured region (the region of α phase with similar crystallographic orientation), the slip behavior was closely related to the same basal slip. The blocked slip aroused a high stress concentration in microtextured region, which was easy to induce the formation of microcrack, and then the microcrack propagated along the slip band. This can be attributed to the fact that slip transmission behavior was closely related not only to the alignment between slip planes and slip directions in two neighboring slip systems, but also to their Schmidt factors (SFs). Thus, the fracture mechanism was the coexistence of micro-void accumulation facture and cleavage fracture.
查看更多>>摘要：? 2022 Elsevier B.V.In present study we developed an effective way to obtain amorphous/nanocrystalline Si in high-capacity Si-based composites for improving their cycle stability as lithium-ion anodes. Amorphous/nanostructured Si@SiOx-Cu3Si composites were synthesized via solid-state reactions using mechanical milling with bulk Si and CuO as starting materials. The microstructural characterization of Si@SiOx-Cu3Si composites demonstrated the phase transformation during the synthesis process of mechanical milling. The ratio and fine-scale distribution of amorphous Si in Si@SiOx-Cu3Si composites were quantitatively analyzed by confocal μ-Raman spectroscopy. The electrochemical properties indicated that Si@SiOx-Cu3Si composites exhibited enhanced cyclability due to containing a highly disordered amorphous Si. Calculated in a full-cell stack model, the lithium-ion cell using Si@SiOx-Cu3Si anodes could provide higher energy density over commercial graphite.
查看更多>>摘要：? 2022 The AuthorsDue to the small mass and anomalously large neutron scattering cross-section of proton (about 80 barns compared to a few barns for other nuclei), inelastic neutron scattering is considered as one of the most effective tools in studying optical vibrations of hydrogen atoms in metal hydrides. The current review is focused on the binary hydrides of 3d- and 4d-metals of groups VI–VIII, which were produced at high hydrogen pressures of several gigapascals in relatively large quantities of hundreds of mg, quenched to low temperature and studied by INS ex situ at ambient pressure with high statistical accuracy. One of the unusual effects revealed by INS is a strong increase in the strength of the metal-hydrogen interactions with decreasing atomic number of the d-metal accompanied by an increase in the Me-H distance. Based on the available experimental results, the spectra g(E) of the phonon density of states and temperature dependencies CV(T) of the heat capacity at constant volume at T up to 1000 K have been derived in this paper and presented both in the figures and in digital form. This provides the reference data for the theoretical investigations of the crystal structures and compositions of new practically important hydrides giving the opportunity to validate calculation methods by comparing the calculated g(E) and CV(T) with the accurate experimental dependencies for the binary hydrides. Recent INS studies showed [R.A. Klein et al., J. Alloy. Compd. 894 (2022) 162381] that the fingerprints of anomalously short H-H separations of 1.6 ? violating the “2 ? rule” can be easily and unambiguously identified in the complex INS spectra of quaternary hydrides (La,Ce)NiInH1+x. This makes neutron spectroscopy an attractive means for obtaining valuable data in the search for novel hydrides with a record high hydrogen capacity.
查看更多>>摘要：? 2022 Elsevier B.V.By observing the microstructure, testing the rotating bending fatigue property and analyzing the microscopic deformation characteristics, the effects of heat treatment on grain boundary carbides and rotating bending fatigue property of the K417G nickel-based superalloy were studied. The results show that the rotating bending fatigue property of the alloy is improved by adjusting the precipitation characteristics of grain boundary carbides through the appropriate heat treatment. After aging at different temperatures (850 °C, 900 °C and 950 °C) for 16 h, the previous Zr-rich carboborides at grain boundaries in the as-cast alloy were transformed into M23C6 carbides rich in Cr and Mo. With the increase of aging temperature, the grain boundary carbides gradually changed from continuous chains to dispersed spherical and ellipsoidal grains. The average spacing size of the grain boundary carbides gradually increased from 0.57 μm to 0.74 μm, and the distribution of carbides along the grain boundaries became more and more dispersed and uniform. In the alloys aged at 850 °C and 900 °C, severe dislocation pile-up and stress concentration around the continuous carbide chains at grain boundaries promoted the initiation and propagation of microcracks, resulting in low rotational bending fatigue property. When the alloy was aged at 950 °C, the dispersed grain boundary carbides could not only effectively hinder the grain boundary sliding, but also significantly reduce the dislocation pile-up and stress concentration around the carbides, thereby the rotating bending fatigue property of the K417G superalloy was improved.
查看更多>>摘要：? 2022 Elsevier B.V.ZnFe2O4/graphite composites were synthesized by a high temperature ball milling method. Magnetic properties, electromagnetic response, and microwave absorption properties of the ZnFe2O4/graphite composites with different graphite were investigated by a vibrating sample magnetometer and a vector network analyzer in the 2–18 GHz frequency range. The minimum reflection loss of ZnFe2O4 reached ? 19.72 dB at 13.04 GHz at the absorbent layer thickness of 2 mm, and the effective absorption bandwidth (RL<?10 dB) is 3.52 GHz covering a frequency range from 11.44 to 14.96 GHz. The composite with 10 wt% graphite (ZFO/C10) showed excellent electromagnetic impedance matching performance. The minimum reflection loss of ZFO/C10 composite reached ? 29.85 dB at 17.52 GHz at the absorbent layer thickness of 1.3 mm, and the effective absorption bandwidth (RL<?10 dB) reached 4 GHz covering a frequency range from 13.12 to 17.12 GHz at a thin thickness of 1.5 mm. Compared to the ZnFe2O4, the ZnFe2O4/graphite composites exhibited better microwave absorbing performance and wider effective absorption bandwidth. A possible microwave absorption mechanism for the ZnFe2O4/graphite composites was proposed.
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