Claudio Shyinti KiminamiFrancisco Gil CouryDiego de Araujo Santana
11页
查看更多>>摘要：Medium/High Entropy Alloys (M/HEAs) exit over immense compositional fields, which represent a challenging opportunity for the development of alloys with optimized properties. To realize their potential, we need to be able to predict properties of interest from different compositions effectively. Precipitation strengthened alloys are of wide interest, but their yield strength modeling is not simple because many factors as precipitate type, size, fraction, and composition play important roles. The Cr_(29.7)Co_(29.7) Ni_(35.4)Al_(4.0)Ti_(1.2) (at%) alloy was designed to have a highly concentrated Cr-Co-Ni face centered cubic matrix with Ll_2 precipitates. In the present work, this alloy was aged at 850 °C for times up to 166 h and had its yield strength measured in the different aging conditions through tensile tests. A recently developed model to calculate the solid solution contribution in FCC multi-principal element alloys was coupled with classical grain-boundary strengthening and precipitation hardening models to predict the yield strength of the studied alloy. We show that the different strengthening contributions can be modeled independently with satisfactory accuracy. The results can be easily extrapolated to other alloys of the Cr-Co-Ni-Al-Ti system. An empirical relationship to estimate the room temperature lattice parameter of FCC alloys is also proposed. A promising route to explore the vast compositional space of M/HEA and design new precipitation hardening alloys with optimized mechanical properties is suggested.
查看更多>>摘要：In this work, a novel method of mechanochemistry is used to directly prepare high-performance Ni-Fe based catalysts for oxygen evolution reaction (OER) in an environmental-friendly borate electrolyte with near-neutral pH. Such a procedure is simple, effective, and time-saving. The effect of iron-based raw materials and mechanochemical reaction on OER of catalysts are investigated. It shows that iron nitrate nonahydrate is the best iron resource compared to iron hydroxide and iron oxide due to amorphous iron species in catalysts for strengthening the "Fe inductive effect" and generating active Ni species with high valence. Besides, the grinding time can control the mechanochemical reaction from mixed reaction to solid reaction in the catalyst synthesis process. When the time is 30 min, the catalyst is composed with amorphous Ni(OH)_2 and the precursors of NiFe-LDH. This catalyst only needs 413 mV overpotential to reach 1 mA cm~(-2) in 0.1 M K-Bi (pH=9.2), which is better than precious RuO_2. It is proven that the mechanochemical approach is an alternative method for synthesizing superior OER catalysts.
查看更多>>摘要：Electrically-assisted manufacturing (EAM) has been proved to be very efficient in homogenizing the alloy with heterogeneous grain distribution due to the local Joule heating effect, which completely differs from the common heat treatment. However, the interaction between pulsed current and texture evolution during deformation have been rarely investigated even though texture is critical for the plastic behaviour of anisotropic material. Here, the effect of pulsed current on texture evolution behaviour has been studied by comparing the evolution behaviours of a Ni-based superalloy under electrically-assisted and quasi-static tension. The result showed that the evolution of easy-to-deform texture into hard one was promoted by the pulsed current, but the further enhancement of the hard-to-deform texture's intensity was inhibited. This difference could be attributed to the more pronounced local Joule heating effect in the hard-to-deform grain due to larger lattice distance here, and then the softened hard-to-deform grain could rotate itself towards other orientations more easily. This is called "target effect" of pulsed current on the hard-to-deform texture in present work, which further indicates that EAM is effective in the control of homogeneous behaviour of anisotropic materials not only from the microstructure distribution but also from the mechanical property.
查看更多>>摘要：LiPSs shuttle effect and cycling decay are still considered the main bottlenecks towards the practical application of Li-S batteries as commercial batteries. In the paper, we designed hollow SrTiO_3 microspheres wrapped by reduced graphene oxide (SrTiO_3@rGO) as efficient sulfur host materials with the aim of suppressing LiPSs shuttle and improving cycling stability of Li-S batteries. The hollow SrTiO_3 microspheres wrapped by rGO, with appropriate binding energy to LiPSs, provide balancing surface adsorption and diffusion of LiPSs on nonconductive SrTiO_3 and then promote its conversion on the interface, thus inhibiting the shuttle effect and greatly minimizing the active material irreversible loss in charge/discharge process. Meanwhile, the conductive rGO tightly wrapped on the surface of SrTiO_3 offers an interconnected conductive network to support the fast electron/ion transfer. Profit from these merits, the SrTiO_3 @rGO as sulfur host manifested superior cycling stability with a meager capacity decay rate of 0.0398% per cycle after 500 cycles at 0.2 C and an ultralow decay rate of 0.024% per cycle after 600 cycles at 1 C The superior cycling stability suggested the hollow SrTiO_3 @rGO was a potential candidate for the cathode of high-performance Li-S battery.
查看更多>>摘要：The variations in local yield strength and plasticity of a Zr-based bulk metallic glass at different Active temperatures (T_f are studied. To probe the size and distribution of microscopic carriers of plasticity, spherical-tip nanoindentation and microindentation are employed. With nanoindentation, events signifying the departure from Hertzian elastic contact, which manifest as pop-ins in the load-displacement response and correspond to incipient plasticity, are recorded and analyzed. Results indicate that with increasing T_f, the incipient plastic event and the number of subsequent pop-ins increases. Using statistical analysis of the scatter in strength, the activation parameters for shear transformation zones (STZs) in all specimens are determined. By considering the linear accumulation of STZs to form a shear band, the increase in shear yield strength along with plasticity, with increasing T_f, is explained.
查看更多>>摘要：Positron beam-based Doppler broadening results on He ion-implanted FeCrCoNi show distinct changes in defect-sensitive S-parameter corresponding to the formation of helium-vacancy complexes, nucleation/ growth of helium bubbles, and finally the helium bubble rupture, with isochronal annealing. Data analyses of the positron beam-based ratio curves provide clear information on the kinetics of bubble growth and rupture. The difference data in S-parameter (AS), which corresponds to the bubble growth, displays a maximum at 1123 K, with annealing temperature. Comparing the AS value to that reported for nickel, it is concluded that FeCrCoNi has higher bubble growth resistance than nickel.
查看更多>>摘要：Designing nanostructured electrocatalysts plays an important role in improving the electro-catalytic behaviors of energy storage devices. Achieving the high specific capacitance of these devices depends on the structure of nanomaterials and their synthesis process. Herein, we report a novel system consisting of 2D layered materials and ID nanowire with desirable properties suitable for supercapacitor applications. Nickel-Cobalt layered double hydroxide (Ni-Co LDH)@Silver nanowire (Ag NWs)/graphitic carbon nitride (g-C_3N_4) nanomaterial was successfully synthesized using hydrothermal and ultra-sonication methods. The structural studies of the synthesized Ni-Co LDH based electrode materials are characterized by using different analytical techniques namely, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscopy (FE-SEM), High-resolution transmission electron microscopy (HR-TEM), Energy dispersive spectroscopy (EDAX). The electrochemical performance of Ni-Co LDH@Ag NWs/g-C_3N_4 hybrid electrode is investigated using Galvanostatic charge-discharge (GCD), cyclic and voltammetry (CV) techniques. The designed 3D nanostructured composites (Ni-Co LDH@Ag NWs/g-C_3N_4) showed high specific capacitance of 848.5 F/g at a current density at 1 A/g as good cyclic stability after 2000 cycles charge-discharge duration (93.5% at current density 5 A/g).
查看更多>>摘要：Bismuth (Bi)-doped glasses have the potential to be applied in tunable photonic devices owing to their broadband near-infrared (NIR) luminescence. However, it is still challenging to develop Bi-doped glasses with luminescence performance at desirable emission wavelength since it is hard to stabilize the specific luminescent Bi centers. In this work, a structural model describing the negatively charged local environments is proposed to stabilize the activated Bi centers by adding Ta_2O_5 and/or Al_2O_3 in Bi-doped silicate glasses. The results show that the structural model leads to great enhancement of the NIR emission, the broadening of the emission bandwidth and the blueshift of the emission peak, compared to the samples without Ta_2O_5/Al_2O_3 doping. The change in NIR emission performances could originate from the generation of active Bi~+ centers. The latter arises from oxidation of Bi° induced by the negatively charged local environments around Bi. Moreover, the intensity of the Bi NIR emission is enhanced, and this is attributed both to the suppression of phase separation by adding Ta_2O_5 and to the dispersing effect of alumina.
查看更多>>摘要：The adjustment of the antiferroelectricity of a perovskite cell and the reversibility of antiferroelectric (AFE) -ferroelectric (FE) phase transition under electric field is very important for achieving excellent energy storage properties in AFEs. In this work, obvious change of antiferroelectricity was found in novel Na(Nb_(1-x)Sb_x)O_3 lead-free ceramics fabricated via a conventional solid-state reaction method. Repeatable double P-E loops with large E_(A-F) -28 kV/mm and large E_(F.A) -10 kV/mm were obtained in the x = 0.1 ceramic with AFE P phase at room temperature, resulting in excellent energy storage properties with W_(rec) -3.4 J/cm~3, large C_D -366 A/cm~2, high P_D -26 MW/cm3 as well as fast discharge rate t_(0.9) -75 ns. The multiscale structure analysis results indicate that the increased antiferrodistortive (oxygen octahedral tilting) degree and the decreased off-centering displacements of B-site cations after the substitution of Sb for Nb make the main contributions to the achievement of stable AFE phase and reversible AFE-FE phase transition in this work. The Na(Nb_(1-x)Sb_x)O_3 ceramics with excellent energy storage properties show large potential for the next-generation pulse power capacitor applications, and the mechanism for modulating antiferroelectricity found in this work would provide guidance for designing high-performance AFEs.
查看更多>>摘要：The evolution of the crystallographic orientation and the microstructures in triangular adapters of grain continuators (GCs) with different flare angles and thicknesses prepared by a 3rd-generation single crystal (SX) superalloy were investigated under different withdrawal rates. The microstructures were observed by an optical microscope and the crystallographic orientation of the GCs was measured by electron backscatter diffraction (EBSD). The directional solidification process was simulated by a commercial simulation software ProCAST The experimental results showed that the [001] misorientation between both sides of the GCs at top cross section increased with the increasing of the flare angle, the thickness of specimens, and the withdrawal rate. These phenomena were attributed to the changing of the isotherm morphology in the mushy zones and the velocity of the solidification front. As for a low flare angle, the freckle defect formed at one side of specimens under the withdrawal rate of 1 mm/min. With the increasing of flare angle, the freckle defect cannot be found at the same position of the specimens. The formation mechanisms of freckle defect in the triangular adapters of GCs were further discussed.
NSTL
Elsevier