Kovalev, I. D.Kuskov, K., VKovalev, D. YuVergunova, Yu S....
13页
查看更多>>摘要：A powder of equiatomic CoCrFeNiCu high entropy alloy (HEA) was prepared by short-term (120 min) high energy ball milling (HEBM). Our structural and chemical analysis showed that microsized particles of fcc CoCrFeNiCu with a grain size of 8 nm were obtained after 120 min of HEBM at 694/1388 rpm. The structural/phase evolution of CoCrFeNiCu HEA powder and its thermal stability were explored by high-temperature XRD at 600 degrees C, 800 degrees C and 1000 degrees C, by DSC up to 1500 degrees C, through the consolidation by SPS at 800 degrees C and 1000 degrees C, and characterized using XRD, SEM and EDX analyses. In-situ HT XRD analysis during 5.5 h of annealing showed the involvement of transient phases: the bcc phase that appeared in 1 h of annealing at 600 degrees C and disappeared at higher temperatures; and the fcc(1) phase (Cu-rich) arising in 2 h of annealing at 800 degrees C and disappearing at 1000 degrees C in 3 h of annealing. SPS consolidation at 1000 degrees C and annealing at 1000 degrees C for 5.5 h were found to result in the formation of single-phase fcc(2) CoCrFeNiCu alloy with a lean amount of Cu. The melting points for Cu-rich and Cu-depleted HEAs were found as 1118 degrees C and 1288 degrees C (Calphad calculations) and 1115 degrees C and 1365 degrees C (DSC measurements), respectively. SPS consolidation at 1000 degrees C under a pressure of 50 MPa yielded the single-phase fcc CoCrFeNiCu0.5 alloy that turned thermodynamically more favorable than the equiatomic one. Thus, we can suppose thereupon, that the equiatomic fcc phase that appears after 120 min of HEBM is metastable because of the excess of Cu atoms. During annealing in the temperature range 800-1000 degrees C, the Cu-rich fcc(1) phase precipitates from the initial single-phase alloy, while the "mother phase" transforms into the more stable Cu-depleted fcc(2) phase. The chemical compositions of Cu-depleted and Cu-rich phases for the SPS-consolidated HEA CoCrFeNiCu alloy (at 800 degrees C) were determined from TEM-EDX analyses. Optimal combination of short-term HEBM and SPS consolidation can be recommended as a facile route to fabrication of single-phase fcc equiatomic CoCrFeNiCu HEA powders and bulk materials with good structural/elemental homogeneity. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The recent electronic appliances and hybrid vehicles need a high energy density supercapacitor that can deliver a burst and a quick power supply. The high energy density supercapacitor can be obtained by de-signing proper electrode materials along with appropriate electrolytes. This review begins with different mechanisms of energy storage, giving a brief idea regarding how to design and develop different materials to achieve proper electrodes in the pursuit of high-energy density supercapacitor without compromising its stability. This review later focuses on the engineering of different electrode materials like conducting polymer, metal oxides, chalcogenides, carbides, nitrides, and MXenes. Lastly, the hybrid electrodes made up from composites between graphene and other novel materials were investigated. The hybrid electrodes have high chemical stability, long cycle life, good electronic properties, and efficient ionic transportation at the electrode-electrolyte interface, showing great potential for commercial usage. (c) 2021 Elsevier B.V. All rights reserved.
Shkodich, N. F.Kuskov, K., VKovalev, I. D.Vergunova, Yu S....
12页
查看更多>>摘要：Refractory TaTiNb, TaTiNbZr, and TaTiNbZrX (X = Mo, W) high entropy alloys were synthesized by combined use of high energy ball milling (HEBM) and spark plasma sintering (SPS). Powders of predominantly bcc TaTiNbZrX (X = Mo, W) refractory high entropy alloys (RHEAs) were successfully prepared by short-term HEBM (60 min) and then SPS-consolidated at 1373 K for 10 min. TEM analysis of the TaTiNbZrW HEA powder obtained after 60 min of HEBM revealed its nanocrystalline structure with an average grain size of up to 50 nm and predominantly uniform distribution of the elements on an atomic scale. The SPS consolidation at 13000C led to an increase in grain sizes up to 100-300 nm. Thus prepared bulk RHEA materials showed ultra-high Vickers hardness of 8.5 GPa and 13 GPa for TaTiNbZrMo and TaTiNbZrW alloys, respectively. The room-temperature compressive strength of TaTiNbZrW RHEA alloy sintered from HEBM powders attained a value of 2665 \MPa, which is 30% higher than that for the same alloy produced from nonmilled powders. Bulk samples of synthesized RHEA show a higher electrical resistivity (r) compared to the samples prepared from non-milled powder blends. Within the temperature range 298-573 K, the maximum r value for TaTiNbZrW RHEA alloy was found to vary between 132 and 143.6 Omega cm. A decrease in thermal conductivity was observed: (a) upon introduction of Zr, Mo, and W atoms to TaTiNb-based alloys due to additional phonon scattering on lattice distortions caused by different radius and mass of Zr, Mo, and W atoms and (b) for the HEBM-prepared bulk alloys because of additional phonon scattering on the surface of mechanocomposites. (c) 2021 Published by Elsevier B.V.
查看更多>>摘要：In this study, the crystal structure and phase stability of gas atomized equiatomic AlCoCrFeNi powder was investigated. This alloy is usually described as a high entropy alloy forming a solid solution phase stabilized by a high mixing entropy. However, thermodynamic calculations show that the high entropy phase is stable only at very high temperatures close to the melting point and that a mixture of several phases are the most stable state at lower temperatures. This suggest that kinetic effects may influence the phase composition of atomized powder. The unique features of X-ray diffraction, neutron diffraction as well as transmission electron microscopy were used to study the atomic structure of the atomized powder in detail. The results show that the powder crystallises in an ordered B2 (CsCl-type) structure with a preferred site occupation of Al and Fe on the (1/2 1/2 1/2) position and Co and Ni on the (0 0 0) position. During heat-treatment of the powder, the B2 phase decomposes into fcc and sigma phases and the final phase composition is highly dependent on the heating rate. The effect of heat-treatment on the atomized powder was also investigated and revealed a significant phase transformation with e.g. the formation of sigma phase preferably at the surface of the powder particles. The phase content was also dependent on the size fraction of the powder particles. Sintering of green bodies made with different heat cycles showed that the phase composition of the starting material had a significant impact on the final phase composition and microstructure of the sintered components. The results illustrate the importance of well-defined powder materials for powder consolidation, especially additive manufacturing (binder jetting) of high entropy alloys. (C) 2021 Published by Elsevier B.V. CC_BY_4.0.
查看更多>>摘要：Tin sulfide (SnS) has been regarded as one of the most attractive anode materials for lithium-ion batteries (LIBs) because of its high specific capacity. However, its large volume expansion (> 300%) and low electronic conductivity restrict its application. In this study, Sn2+ was anchored on Ti3C2 nanosheets through electrostatic attraction, and Ti3C2@SnS@C was synthesized through a hydrothermal method. The obtained Ti3C2@SnS@C exhibits excellent rate performance and cycle performance and effectively serves as an anode material for LIBs. It has a stable capacity of 563.5 mAh/g after 420 cycles at 500 mA/g, and this value is much higher than that of commercially available anode materials. Ti3C2 can also effectively inhibit the volume expansion of SnS particles. The volume expansion of Ti3C2@SnS@C electrode is only 56.8% after 420 cycles at 500 mA/g. This finding is much better than that of pure SnS@C electrode (209.3%). (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In the present work, multi-objective evolutionary (MOE) algorithm and machine learning (ML) techniques were employed to predict the age-hardening behavior of aluminum (Al) alloys in a wide range of processing conditions. For this purpose, data containing hardness, information on alloy compositions, and aging conditions (aging time and temperature) were extracted from previous works that reported the age-hardening of Al-Cu-Mg base alloys. Accordingly, 1591 cases were collected for various alloy compositions and processing conditions. Composition features (140) generated based on the alloy composition and element properties (atomic weight, electronegativity, etc.), and processing features (time and temperature) were subjected to a preprocessing using the MOE algorithm to reduce the number of features and use those which highly influence the hardness. MOEprocessed features and counterpart hardness values are then employed in the learning process using various ML algorithms, including decision tree (DT), deep learning (DL), linear general model (GM), gradient boosted trees (GBT), random forest (RF), and support vector machine (SVM). The results show that the MOE algorithm's leveraging with ML learning processes can be successfully used to refine the features and build accurate ML predictive models compared to those created using other feature selection and preprocessing methods. In addition, the learning results showed that the predictive model built using the ensemble GBT algorithm exhibits the best performance among all models built based on other ML algorithms, where a relative error of 3.5% was recorded for the GBT-based model, and it could reproduce the experimental aging behavior of Al alloy. (c) 2021 Published by Elsevier B.V.
查看更多>>摘要：To balance the core loss and permeability of soft magnetic composites (SMCs), a Co-Ba composite ferrite insulation layer was employed to clad the surface of reduced iron powder by sol-gel method. The successful preparation of the honeycomb-like Co-Ba composite ferrite coating layer was verified by scanning electron microscopy (SEM), the composition of the coating was determined by X-ray diffraction (XRD), and the magnetic properties were tested with a B-H curve analyzer. BSEM images of the polished cross-section and core loss separation results confirmed that an excessively high annealing temperature causes the composite ferrite insulation layer to fail. A high effective permeability of up to 121 at 300 kHz and low core loss (P-cv) of 129 kW/m(3) at 100 kHz and 0.02 T were obtained in prepared samples at the optimized annealing temperature of 500 degrees C. Subsequently, simulation analysis based on the Clausius-Maxwell formula model was used to confirm the feasibility of the enhancement on effective permeability in Fe@Co-Ba composite ferrite theoretically. The agreement between simulation and experimental results further indicated that a good balance between the core loss and permeability of Fe-based SMCs was achieved by Co-Ba composite ferrite cladding. (C) 2021 Elsevier B.V. All rights reserved.
Park, TaesungJavadinejad, Hamid RezaKim, Young-KukChang, Hye Jung...
17页
查看更多>>摘要：(Y-La-Ce-Nd-Gd)(2)O3+beta high-entropy rare earth oxides (HE-REOs) were synthesized using both mechanochemical (ball milling) and chemical (sol-gel) methods. Energy-dispersive X-ray spectroscopy revealed that the compositional uniformity of the as-synthesized powders was the highest in the sol-gel process, followed by that in wet milling and dry milling. The sol-gel process was advantageous because it yielded oxide powders with the best compositional uniformity and required a lower annealing temperature to obtain a single phase compared to the ball-milled powders. However, following heat treatment at 1600 degrees C, similar chemical uniformity and physical properties of the oxides were obtained regardless of the synthesis method. The formation of single-phase Ia3 structures was confirmed by X-ray diffraction and Rietveld refinement analyses. A detailed transmission electron microscopy analysis revealed that a Fm3m structure formed at low temperatures. The thermodynamic parameters of high-entropy alloys, high-entropy transition metal oxides, and HE-REOs were calculated and compared. This analysis confirmed that the HE-REOs synthesized in the present study had very high phase stability. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The slow kinetics of oxygen evolution reaction (OER) severely restricts the application of water splitting. In this paper, a free-standing serrated Ni-WO3 electrode for OER was synthesized by a simple in-situ etching method using (NH4)(2)SO4 as etchant. The effect of etchant on structures of Ni-WO3 were studied carefully, indicating that the NH4+ and SO42-have a synergistic effect on the unique structure. The serrated Ni-WO3-3 (where 3 is the mass of (NH4)(2)SO4) dramatically enhance OER performance, an over-potential of only 265 mV at 10 mA cm(-2) as compared with that 365 mV of serrated-free Ni-WO3. Interestingly, the structure and composition of the serrated Ni-WO3 electrode undergoes a self-reconstruction process during OER, the finally catalyst is interconnected by low crystallinity nickel oxy-hydroxide nanoparticles. This work mainly explores the influence of etching agent type, usage and reaction time on the morphology and properties of materials, and the reconstruction phenomenon in OER pre-catalyst was confirmed. (C) 2021 Published by Elsevier B.V.
Hariyadi, ArifSuwarno, SuwarnoDenys, Roman, Vvon Colbe, Jose Bellosta...
11页
查看更多>>摘要：Hydrides of the AB(2) Laves type alloys (A=Zr, Ti; B = transition metal - Fe, Co, Ni, Mn, Cr, V) have been extensively studied as materials for the storage of gaseous hydrogen. They contain up to 4 H atoms/formula unit AB(2), thus achieving reversible H storage capacities in the range between 1.5 and 2.0 wt% H and offering high rates of hydrogen charge and discharge, thus making them suitable for designing efficient hydrogen stores operating at ambient conditions. In the present study, we performed an experimental study and modeling of the thermodynamics and the kinetics of interaction in the AB(2)-hydrogen system. The experimental data was collected by studying a model alloy with a composition Ti0.15Zr0.85La0.03Ni1.126Mn0.657V0.113Fe0.113. Hydrogen absorption and desorption were studied in a volumetric Sieverts type apparatus at isothermal conditions using a single-step change/discharge and stepwise methods. The results obtained from the model simulation show that the reaction follows the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, with the value of exponent n = 1-1.25 for absorption and 1 for desorption. This indicates that the rate-limiting hydrogen absorption and desorption steps are jointly governed by hydrogen diffusion and grain boundary nucleation of alpha-solid solution and beta-hydride. The activation energies for both hydrogen absorption and desorption decrease along with increasing hydrogen content in the hydride. (C) 2021 The Authors. Published by Elsevier B.V.
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