查看更多>>摘要：? 2022 Elsevier B.V.This work prepared a new type of Ce2[Zr1-x(Al1/2Nb1/2)x]3(MoO4)9 (CZ1-x(AN)xM) (x = 0.02–0.10) microwave dielectric ceramics through the solid-phase process. CZ1-x(AN)xM ceramics exhibited low dielectric constant, ultra-low dielectric loss, and near-zero resonant frequency temperature coefficient, which is suitable for 5 G technology. The effects of (Al1/2Nb1/2)4+ replacing Zr4+ on the sintering characteristics, crystal structure, and microwave dielectric properties of Ce2Zr3(MoO4)9 (CZM) ceramics were studied systematically. In this work, CZ1-x(AN)xM could form a pure crystal structure in the whole doping range according to the X-ray diffraction pattern. The crystal cell parameters of the ceramics were confirmed by Rietveld refinement analysis. Furthermore, the surface morphology of CZ1-x(AN)xM sintered at the optimum sintering temperature was studied by scanning electron microscopy. Some internal parameters of the ceramics were calculated and analyzed by employing the P-V-L theory. The theoretical loss was acquired by employing an infrared reflection spectrometer. When x was 0.04 and the sintering temperature was 850 ℃, the best properties were achieved, including εr = 10.54, Q·f = 91,476 GHz (at 9.55 GHz), and τf = ? 8.95 ppm/℃. This work studied the relationship between lattice vibration and microwave dielectric properties and discussed the influence of ion doping on microwave dielectric properties from the perspective of chemical bonds, laying a theoretical foundation for related research.
查看更多>>摘要：? 2022 Elsevier B.V.In the present study, nitrogen-doped vertically aligned carbon nanotubes (N-VACNTs) were synthesized on carbon cloth (CC) using the floating catalyst chemical vapor deposition (FCCVD) method, and MnO2 nanosheets were grown on them using the hydrothermal method to produce an N-VACNT@MnO2 nanocomposite structure. In this structure, a synergistic effect was obtained by combining N-VACNTs, which allow high electrical conductivity and fast ion transfer. In the galvanostatic charge-discharge (GCD) measurements performed separately in a three-electrode test cell using 1 M of Na2SO4 electrolyte, the specific capacitance of the N-VACNTs was found to be 53.7 F g?1 at a current density of 0.5 A g?1, and the specific capacitance of the N-VACNT@MnO2 electrode structure was found to be 497 F g?1. In addition, after 10,000 charge-discharge cycles at a current density of 10 A g?1, the N-VACNT electrode retained 99 % of its initial specific capacitance, while the N-VACNT@MnO2 electrode exhibited outstanding cyclic stability with 76 % of its initial specific capacitance. Moreover, in the as-fabricated asymmetric supercapacitor (ASC) using N-VACNTs and N-VACNTs@MnO2, the negative and positive electrodes achieved a stable voltage window of 0–1.7 V, with a specific capacitance of 59.4 F g?1 at a current density of 1 A g?1. Additionally, this ASC showed good cycling stability retaining 84 % of its specific capacitance at the end of 10,000 cycles. Therefore, this ASC structure with an energy density of 24.7 Wh kg?1 and a power density of 15.7 kW kg?1 are promising electrode materials for energy storage.
查看更多>>摘要：? 2022 Elsevier B.V.This work investigated the influence of the grain morphology and crystallographic orientation on the mechanical anisotropy of a laser powder bed fusion produced (L-PBFed) Ti-41 Nb alloy using pre-alloyed alloy for dental implants. The microstructure of L-PBFed Ti-41Nb alloy consists of columnar grains of a high aspect ratio with a strong< 001 > preferred orientation along the building direction (BD). To evaluate the mechanical anisotropy of L-PBFed Ti-41 Nb alloy, the external loading was compressed either perpendicular or parallel to BD (i.e., horizontal and vertical samples, respectively). Compression results show that the compressive yield strength (CYS) of horizontal samples is significantly higher than that of vertical samples. At the early stage of deformation, obvious {332}< 113 > mechanical twins are preferentially detected in the nearly< 001 > orientated grains along the compression axis. The dominant reasons for the lower CYS of vertical samples can be attributed to the easier activation of {332}〈113〉 mechanical twins in the typical columnar grains with strong< 001 > crystallographic orientation. It is suggested that the anisotropy of the L-PBFed alloy can be utilized through simple position control such as adjustment of the BD and reasonable structural design.
查看更多>>摘要：? 2022 Elsevier B.V.Chemical solution deposition is becoming one of the most promising routes toward cost-effective production of REBa2Cu3O7?z (REBCO) based high temperature superconducting tapes. However, a comprehensive understanding of nucleation and growth for REBCO films with dopants, especially considering low sintering temperature and high reproducibility, is still far from being achieved. In this work, dilute Co was introduced into fluorine-free precursor, and comparison studies of a set of pristine and doped GdBCO films were carried out. Correlation between texture, microstructure and critical current density were established, and nucleation & growth mechanism for doped films were proposed. By comparison, Co doping enables to reduce the textured temperature about 50 ℃ because of the dramatically decreased decomposition temperature of intermediate phase BaCO3, which facilitate Ba-Cu-O liquid phase transformation and thus GdBCO epitaxial growth at lower temperatures. These results bring particular opportunities for fine tuning of the film fabrication process by incorporating dilute impurities in precursors.
查看更多>>摘要：? 2022 Elsevier B.V.The speciation and morphology of U carbide inclusions in pre- and post-melt U metal have been explored using high-resolution analytical electron microscopy (AEM). This report presents Part 2 of our study, in which aberration (Cs) corrected transmission and scanning transmission electron microscopies (S/TEM) were used to elementally and crystallographically characterize C-containing impurities and defect features in U samples for comparison with results obtained by scanning electron microscopy (SEM) in Part 1, previously published by this journal. Elemental mapping and unit cell matching of inclusions by S/TEM are consistent with phases observed by SEM, and new dislocations can be observed associating with some inclusion morphologies but not others.
查看更多>>摘要：? 2022 Elsevier B.V.Although C impurities in U have been studied for decades, fundamental questions regarding their incorporation, migration, and transformations during metal processing still exist. In two written Parts, we compare the chemical speciation, distributions, crystallography, and morphologies (e.g., size and shape) of C-containing impurities in U metal both before and after melting using high-resolution analytical electron microscopy (AEM). This first Part demonstrates the variability of carbide inclusions in U metal with respect to their chemical phases and morphologies as observed by scanning electron microscopy (SEM). A variety of inclusion types, such as the pill-shaped U monocarbide (UC), previously only hypothesized, are summarized. Additionally, delineation between hopper-shaped U carbonitride U(C,N) and dendritic U carbide inclusions is discussed in relationship to historic literature.
查看更多>>摘要：? 2022 Elsevier B.V.WC composites with 5 wt% TiC0.4 were fabricated by spark plasma sintering (SPS) at sintering temperature of 1400–1700 °C for 10 min under an external pressure of 50 MPa. It can be observed that the WC-5 wt% TiC0.4 composites mainly consisted of WC phase and non-stoichiometric (W1?x, Tix)Cn solid solution phase and the amount of WC dissolving in TiC0.4 increased with sintering temperature. The (W1?x, Tix)Cn solid solutions uniformly distributed around WC grains and formed a semi-coherency interface with WC, which restricted the growth of WC grains and enhanced mechanical properties of the WC-5 wt% TiC0.4 composites. The average grain size of WC (251.5 ± 201.6 nm) in WC-5 wt% TiC0.4 composite sintered at 1600 ℃ was considerably smaller compared to most of previously reported WC-based composites. The existence of high content of C vacancies in non-stoichiometric TiC0.4 raised remarkably the diffusion rate of W and Ti atoms in the sintering process of WC-5 wt% TiC0.4 composites in contrast with stoichiometric TiC. The WC-5 wt% TiC0.4 composite sintered at 1600 ℃ possessed the optimum properties, with the hardness of 21.9 GPa, fracture toughness of 7.6 MPa·m1/2, flexural strength of 612 MPa and compressive strength of 2.7 GPa. Moreover, it can be confirmed that the oxidation resistance of WC-5 wt% TiC0.4 composite at higher temperature outperformed that below 1218 ℃. In addition, the WC-5 wt% TiC0.4 composite sintered at 1600 ℃ showed higher high-temperature hardness, lower thermal conductivity and better resistance to oxidation than those of conventional WC-Co composites.
查看更多>>摘要：? 2022 Elsevier B.V.The hot compressive deformation behavior of Co-free Fe2.5Ni2.5CrAl multi-principal element alloys (MPEAs) was investigated in the temperature and strain rate ranges of 800–1100°C and 0.001 s?1 and 1 s?1, respectively. Microstructural observations were carried out by optical microscopy (OM) and electron backscatter diffraction (EBSD). A constitutive model based flow-stress analysis was carried out, the activation energy (Q) was obtained as 315.9 kJ/mol at steady state. The strain rate sensitivity (m), the power dissipation (η), and instability parameter (ξ) were utilized to construct the processing maps. Power-law breakdown and unstable flow occurred at the high strain rates at which strain hardening was pronounced. The optimal condition for successful hot working was determined to be at strain rates in the range of 10?2–10?3 s?1 and a temperature range of 850 ~ 1020°C. FEM simulations revealed the strain and stress distribution during hot deformation and predicted instabilities during hot forming. The main deformation mechanism was dislocation climb with a stress exponent n > 5. The Q value for plastic flow in the power-law creep regime was calculated considering the effect of lattice diffusion of atoms and was in accordance with the measured Q value. Thus, our study revealed the hot working characteristics and the optimum processing parameters for successful hot working of Fe2.5Ni2.5CrAl MPEAs.
查看更多>>摘要：? 2022 Elsevier B.V.Cu alloys with high strength, high electrical conductivity (EC) and good softening resistance (SR) are urgently needed in many fields. A Cu-1.06 wt% Fe-0.44 wt% Ti alloy was designed concerning the calculation of phase diagrams. It was expected that the Fe2Ti phases could precipitate to obtain high performance. The designed alloy was prepared and it obtained the most excellent properties of 211 HV hardness, 542 MPa tensile strength, 9.8% uniform elongation, 79% IACS EC and 575 °C softening temperature after solid solution, cold rolling (90% reduction of thickness) and aging at 450 °C for 24 h. The Fe2Ti phases indeed precipitated in the Cu matrix, which proved the alloy design idea. The precipitation kinetics, interaction between recrystallization and precipitation, and the effects of precipitation on strength, EC and SR were discussed. It was concluded that the precipitation driving force of the Fe2Ti phase itself in Cu was weak, and the cold rolling could significantly promote the precipitation. The precipitation of Fe2Ti slowed down the recrystallization to a certain extent. The high strength and high EC were mainly due to the precipitation strengthening and purification effects of the Fe2Ti precipitation on the Cu matrix. Besides, the good SR was mainly due to the low diffusion rate of Fe in Cu and the weak precipitation driving force of Fe2Ti.
查看更多>>摘要：? 2022 Elsevier B.V.A recently developed sulfide solid electrolyte in lithium solid-state batteries has a low critical current density, which can cause battery failure. Therefore, the metal oxide substitution in the Li-argyrodite structure was considered as a strategy to enhance the interface stability. In this work, the interface stability of the Li-argyrodites was improved using metal and oxygen substitution in the P- and S-sites of the Li6PS5Cl structure; furthermore, their structural and electrochemical performances were evaluated. For this study, the MoO2 substituted argyrodite (0 ≤ x ≤ 0.2) was synthesized using a high-energy ball-milling process. Structural analysis revealed that impurity phases occurred when x was over 0.05; this indicated the solubility limit of the metal oxide substitution. The ionic conductivity analysis demonstrated that Li6PS5Cl-MoO2-0.05 electrolyte maintained an ionic conductivity of 4.16 mS cm?1. Additionally, the Li6PS5Cl-MoO2-0.05 composition exhibited a higher critical current density (0.55 mA cm?2) than that of Li6PS5Cl (0.20 mA cm?2). It should be further noted that the electrochemical performances were examined against lithium as a reference.
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