Microstructure and properties of Ag–Ti_3SiC_2 contact materials prepared by pressureless sintering

Ti3SiC2-reintbrced Ag-maJxix composites are expected to serve as eleclrical contacts. In this study, the wettability of Ag on a Ti3SiC2 subslxate was measured by the sessile drop melkod. The Ag-Ti3SiC2 composites were prepared from Ag mad Ti3SiC2 powder mix- tures by pressureless sintering. The effects of compacting pressure （100-800 MPa）, sintering temperature （850-950~C）, mad soaking time （0.5-2 h） on the microslxucture mad properties of the Ag-Ti3SiC2 composites were investigated. The experimental results indicated that Ti3SiC2 paxticulates were uniformly distxibuted in flae Ag matrix, wiflaout reactions at the interthces between flae two phases. The prepared Ag-10wt%Ti3SiC2 had a relative density of 95% mad an electrical resistivity of 2.76 x 10 3 m~）＇cm when compacted at 800 MPa mad sintered at 950~C for 1 h. The incorporation of Ti3SiC2 into Ag was found to improve its hardness without substantially compromising its electrical conductivity; INs behavior was attxibuted to the combination of ceramic and metallic properties of the Ti3SiC2 reinforcement, suggesting its potential application in electrical contacts.

Porous nanostructured ZnCo2O4 derived from MOF-74:High-performance anode materials for lithium ion batteries

Nanostructured metal oxides derived from metal organic frameworks have been shown to be promising materials for application in high energy density lithium ion batteries. In this work, porous nanostructured ZnCo2O4and Co3O4were synthesized by a facile and cost-effective approach via the calcination of MOF-74 precursors and tested as anode materials for lithium ion batteries. Compared with Co3O4, the electrochemical properties of the obtained porous nanostructured ZnCo2O4exhibit higher specific capacity, more excellent cycling stability and better rate capability. It demonstrates a reversible capacity of 1243.2 m Ah/g after 80 cycles at 100 m A/g and an excellent rate performance with high average discharge specific capacities of 1586.8, 994.6, 759.6 and 509.2 m Ah/g at 200, 400, 600 and 800 m A/g, respectively.The satisfactory electrochemical performances suggest that this porous nanostructured ZnCo2O4is potentially promising for application as an efficient anode material for lithium ion batteries.

Effects of highly dispersed Ni nanoparticles on the hydrogen storage performance of MgH_(2)

MgH_(2)with a large hydrogen capacity is regarded as a promising hydrogen storage material.However,it still suffers from high thermal stability and sluggish kinetics.In this paper,highly dispersed nano-Ni has been successfully prepared by using the polyol reduction method with an average size of 2.14 nm,which significantly improves the de/rehydrogenation properties of MgH_(2).The MgH_(2)–10wt%nano-Ni sample starts releasing H_(2)at 497 K,and roughly 6.2wt%H_(2)has been liberated at 583 K.The rehydrogenation kinetics of the sample are also greatly improved,and the adsorption capacity reaches 5.3wt%H_(2)in 1000 s at 482 K and under 3 MPa hydrogen pressure.Moreover,the activation energies of de/rehydrogenation of the MgH_(2)–10wt%nano-Ni sample are reduced to(88±2)and(87±1)kJ·mol−1,respectively.In addition,the thermal stability of the MgH_(2)–10wt%nano-Ni system is reduced by 5.5 kJ per mol H_(2)from that of pristine MgH_(2).This finding indicates that nano-Ni significantly improves both the thermodynamic and kinetic performances of the de/rehydrogenation of MgH_(2),serving as a bi-functional additive of both reagent and catalyst.

Modulating Co-Co bonds average length in Co_(0.85)Se_(1-x)S_(x) to enhance conversion reaction for potassium storage

While alloying transition metal chalcogenides(TMCs)with other chalcogen elements can effectively improve their conductivity and electrochemical properties,the optimal alloying content is still uncertain.In this study,we study the influence of dopant concentration on the chemical bonds in TMC and reveal the associated stepwise conversion reaction mechanism for potassium ion storage.According to density function theory calculations,appropriate S-doping in Co0.85Se(Co_(0.85)Se_(1-x)S_(x))can reduce the average length of Co-Co bonds because of the electronegativity variation,which is thermodynamically favourable to the phase transition reactions.The optimal Se/S ratio(x=0.12)for the conductivity has been obtained from experimental results.When assembled as an anode in potassium-ion batteries(PIBs),the sample with optimized Se/S ratio exhibits extraordinary electrochemical performance.The rate performance(229.2 mA h g^(-1)at 10 A g^(-1))is superior to the state-of-the-art results.When assembled with Prussian blue(PB)as a cathode,the pouch cell exhibits excellent performance,demonstrating its great potential for applications.Moreover,the stepwise K+storage mechanism caused by the coexistence of S and Se is revealed by in-situ X-ray diffraction and ex-situ transmission electron microscopy techniques.Hence,this work not only provides an effective strategy to enhance the electrochemical performance of transition metal chalcogenides but also reveals the underlying mechanism for the construction of advanced electrode materials.

Effect of rare earth on the microstructure and mechanical properties of as-cast Cu-30Ni alloy

Cu-30Ni-xRE （x = 0-0.213） alloys were prepared by a metal mould casting method. The effect of RE on the microstructure and mechanical properties of the alloys was investigated using optical microscope, scanning electronic microscope with energy-dispersive spectrometer, X-ray diffraction, and mechanical test. The results show that RE has obvious effect on refining dendrite structure and grain size, as well as on purifying the melting of Cu-30Ni alloy. With the increase of RE content, the ultimate tensile strength, yield strength, and elongation increase at first and then decrease after adding RE more than 0.095 wt.%. Cu-30Ni-0.095RE alloy possesses preferable mechanical properties, i.e., the ultimate tensile strength, yield strength, and elongation are 308 MPa, 125 MPa, and 51.2%, respectively. The microstructure and mechanical properties are worsened with increasing RE content more than 0.095 wt.%. The improvement of mechanical properties of Cu-30Ni-0.095RE alloy is attributed to RE refining microstructure and purifying the matrix.

Effect of rare earths on corrosion resistance of Cu-30Ni alloys in simulated seawater

Cu-30Ni-xRE(x=0–0.213 wt.%) alloy was prepared by adding rare earths(RE) in melted Cu-30Ni alloy using metal mould casting method.The effects of RE on corrosion resistance of the alloy in simulated seawater were investigated using optical microscope,scanning electronic microscope with energy-dispersive spectrometer and electrochemical measurement system.The results showed that the corrosion resistance of Cu-30Ni alloy was greatly improved by adding proper amount of RE,whereas excess addition of RE worsened ...

Effects of La addition on the microstructure and tensile properties of Al-Si-Cu-Mg casting alloys

The effects of La addition on the microstructure and tensile properties of B-refmed and Sr-modified A1-1 1Si-1.5Cu-0.3Mg cast- ing alloys were investigated. With a trace addition of La （0.05wt%-0. lwt%）, the mutual poisoning effect between B and Sr can be neutral- ized by the formation of LaB6 rather than SrB6. By employing a La/B weight ratio of 2：1, uniform microstructures, which are characterized by well refined ct-A1 grains and adequately modified eutectic Si particles as well as the incorporation of precipitated strengthening intermetal- lics, are obtained and lead to appreciable tensile properties with an ultimate tensile strength of 270 MPa and elongation of 5.8%.

Preparation and properties of thermal insulation coatings with a sodium stearate-modified shell powder as a filler

Waste shell stacking with odor and toxicity is a serious hazard to our living environment. To make effective use of the natural resources, the shell powder was applied as a filler of outdoor thermal insulation coatings. Sodium stearate(SS) was used to modify the properties of shell powder to reduce its agglomeration and to increase its compatibility with the emulsion. The oil absorption rate and the spectrum reflectance of the shell powder show that the optimized content of SS as a modifier is 1.5wt%. The total spectrum reflectance of the coating made with the shell powder that is modified at this optimum SS content is 9.33% higher than that without any modification. At the optimum SS content of 1.5wt%, the thermal insulation of the coatings is improved by 1.0℃ for the cement mortar board and 1.6℃ for the steel plate, respectively. The scouring resistance of the coating with the 1.5wt% SS-modified shell powder is three times that of the coating without modification.

Solidification microstructure of M2 high speed steel by different casting technologies

The present work investigated the solidification microstructure of AISI M2 high speed steel manufactured by different casting technologies, namely iron mould casting and continuous casting. The results revealed that the as-cast structure of the steel was composed of the iron matrix and the M2C eutectic carbide networks, which were greatly refined in the ingot made by continuous casting process, compared with that by the iron mould casting process. M2C eutectic carbides presented variation in their morphologies and growth characteristics in the ingots by both casting methods. In the ingot by iron mould casting, they have a plate-like morphology and grow anisotropically. However, in the ingot made by continuous casting, the carbides evolved into the fiber-like shape that exhibited little characteristics of anisotropic growth. It was noticed that the fiber-like M2C was much easier to decompose and spheroidize after heated, as a result, the carbides refined remarkably, compared with the case of plate-like carbides in the iron mould casting ingot.

Effect of TiO2 pigment gradation on the properties of thermal insulation coatings

This study was designed to evaluate the thermal performance and mechanical properties of coatings with different gradations of TiO2 pigments. The solar reflectance, cooling performance, wash resistance, and film adhesion strength of the coatings were investigated. The influence of TiO2 powder gradation on the final properties of the coatings was studed. The solar reflectance and the thermal insulation were observed to increase with increasing content of nanosized TiO2. The mechanical properties of the coatings, such as their wash resistance and film adhesion strength, were observed to increase with increased incorporation of nanosized TiO2. Such improvements in the properties of the coatings were attributed to the greater specific surface area and lower thermal conductivity of nanosized TiO2 particles compared to normal TiO2 particles.

Effects of helium implantation on mechanical properties of (Al_(0.31)Cr_(0.20)Fe_(0.14)Ni_(0.35)) O high entropy oxide films

It is widely accepted that helium(He) bubbles can prevent dislocations from moving and causing hardening and embrittlement of the material. However, He can affect the mechanical properties of materials in various ways. In this work,ultrafine nanocrystal high entropy oxide(HEO) films with He implantation are prepared by using a radio frequency(RF)reactive magnetron sputtering system to investigate the effects of He bubbles located at grain boundary on the mechanical properties of the films. The mechanical properties of the HEO films are investigated systematically via nanoindentation measurements. The results indicate that the grain boundary cavities induced by He implantation can degrade the hardness,the elastic modulus, and the creep resistance of the HEO films. The mechanical properties of the HEO films are sensitive to the interaction between the He bubbles and the dominating defects.

Structural transitions of 4:1 methanol–ethanol mixture and silicone oil under high pressure

A 4:1(volume ratio)methanol–ethanol(ME)mixture and silicone oil are two of the most widely used liquid pressure-transmitting media(PTM)in high-pressure studies.Their hydrostatic limits have been extensively studied using various methods;however,the evolution of the atomic structures associated with their emerging nonhydrostaticity remains unclear.Here,we monitor their structures as functions of pressure up to∼30 GPa at room temperature using in situ high-pressure synchrotron x-ray diffraction(XRD),optical micro-Raman spectroscopy,and ruby fluorescence spectroscopy in a diamond anvil cell.No crystallization is observed for either PTM.The pressure dependence of the principal diffraction peak position and width indicates the existence of a glass transition in the 4:1MEmixture at∼12 GPa and in the silicone oil at∼3 GPa,beyond which a pressure gradient emerges and grows quickly with pressure.There may be another liquid-to-liquid transition in the 4:1 ME mixture at∼5 GPa and two more glass-to-glass transitions in the silicone oil at∼10 GPa and∼16 GPa.By contrast,Raman signals only show peak weakening and broadening for typical structural disordering,and Raman spectroscopy seems to be less sensitive than XRD in catching these structural transitions related to hydrostaticity variations in both PTM.These results uncover rich pressure-induced transitions in the two PTM and clarify their effects on hydrostaticity with direct structural evidence.The high-pressure XRD and Raman data on the two PTM obtained in this work could also be helpful in distinguishing between signals from samples and those from PTM in future high-pressure experiments.

Effects of geometrical characteristics on defect distributions in alloy components produced by selective laser melting

Selective laser melting(SLM)has been applied to manufacture various alloy components with excellent properties,but its further application is restricted by the intrinsic defects.In this work,the internal defect distributions in samples of three alloys(316L stainless steel,AlSi10Mg and Inconel 718)were investigated respectively,considering the effects of geometrical characteristics of the samples.The defects in the 316L stainless steel sample tend to be formed densely in the central part with large wall thickness,indicating a strong sensitivity to heat accumulation.Contrarily,the Inconel 718 sample shows a higher relative density with homogeneous defect distribution,indicating better formability for the SLM process.For the AlSi10Mg sample,the defect density keeps increasing as the deposition goes on.Typically,the defect density located at sample edges shows an abnormally high level comparing with the inner part,especially in the top sections of AlSi10Mg and Inconel 718 samples.The results are helpful for the geometrical design,the adjustment of building orientation and the further optimization of process parameters in the SLM process.

Solution combustion synthesis of high-entropy metal spinel oxide as oxygen evolution reaction catalyst

High-entropy metal spinel oxide(HEO)is proved to be a promising oxygen evolution reaction(OER)catalyst with high catalytic performance and stability.A short routine synthesis process based on solution combustion synthesis was proposed to prepare(Co_(0.25)Ni_(0.25)Mn_(0.25)Zn_(0.25))Fe_(2)O_(4)spinel HEO in this work.During the process,the products were rapidly synthesized and melted due to the high-temperature reaction,and then quickly crystallized on the surface of nickel foam to form a nano-structure coating.With the aid of nano-scale spinel structure,the overpotential of non-activation HEO electrode reaches 276 mV at the current density of 10 mA·cm^(-2),and after 100 h i-t test,it can be further reduced to 230 mV,which proves the high activity of OER catalysis.The promotion of OER catalytic performance can be attributed to the surface reconstruction caused by the selective element leaching and the boost of oxygen vacancy,leading to the formation of nano-scale flocculation around spinel core after the long-term OER process.This work indicates a special casting process for functional materials and explores the application of rapid crystallization.

Giant anisotropy of magnetic damping and significant in-plane uniaxial magnetic anisotropy in amorphous Co40Fe40B20 films on GaAs(001)

Tuning magnetic damping constant in dedicated spintronic devices has important scientific and technological implications. Here we report on anisotropic damping in various compositional amorphous CoFeB films grown on GaAs(001) substrates. Measured by a vector network analyzer-ferromagnetic resonance (VNA-FMR) equipment, a giant magnetic damping anisotropy of 385%, i.e., the damping constant increases by about four times, is observed in a 10-nm-thick Co40Fe40B20 film when its magnetization rotates from easy axis to hard axis, accompanied by a large and pure in-plane uniaxial magnetic anisotropy (UMA) with its anisotropic field of about 450 Oe. The distinct damping anisotropy is mainly resulted from anisotropic two-magnon-scattering induced by the interface between the ferromagnetic layer and the substrate, which also generates a significant UMA in the film plane.

Role of heat treatment in the improvement of mechanical properties of a high-quality Al-11Si-1.5Cu-0.3Mg casting alloy

The purpose of this study is to prepare a high-quality Al-11Si-1.5Cu-0.3Mg casting alloy with a good combination of strength and ductility. The microstructures of as-cast alloy were tailored by employing combined additives of Al-3wt.%B refi ner, Al-10 wt.%Sr modifi er and trace addition of La element. By using OM and SEM, the characteristics of the morphologies of eutectic Si particles and the fracture surfaces of the alloys after solution treatment and aging treatment were measured. The mechanical properties of the alloys after single-step or twostep solution treatment were investigated by tensile testing, and the quality of casting samples were evaluated by quality index, Q. The results indicate that the alloy with substantially modifi ed microstructures displays an improvement in mechanical properties of 270 MPa in ultimate tensile strength and 6% in elongation. After an optimized two-step solution treatment of 490℃/4h + 505℃/4h, the ultimate tensile strength and elongation can reach 346 MPa and 10%, respectively. Under the aging condition, the elongation maintains a relative high value of 5% together with the strength of about 400 MPa, which is the outstanding combination of strength and ductility.

Fabrication and properties of silver-based composites reinforced with carbon-coated Ti_(3)AlC_(2)

Ti_(3)AlC_(2)-reinforced Ag-based composites,which are used as sliding current collectors,electrical contacts,and electrode materials,exhibit remarkable performances.However,the interfacial reactions between Ag and Ti_(3)AlC_(2) significantly degrade the electrical and thermal properties of these composites.To diminish these interfacial reactions,we fabricated carbon-coated Ti_(3)AlC_(2) particles(C@Ti_(3)AlC_(2))as reinforcement and prepared Ag–10wt%C@Ti_(3)AlC_(2) composites with carbon-layer thicknesses ranging from 50–200 nm.Compared with the uncoated Ag–Ti_(3)AlC_(2) composite,Ag–C@Ti_(3)AlC_(2) was found to have a better distribution of Ti_(3)AlC_(2) particles.With increases in the carbon-layer thickness,the Vickers hardness value and relative density of Ag–C@Ti_(3)AlC_(2) gradually decreases.With a carbon-layer thickness of 150 nm,we obtained the lowest resistivity of Ag–C@Ti_(3)AlC_(2) of 29.4135.5×10^(−9)Ω·m,which is half that of Ag–Ti_(3)AlC_(2)(66.7×10^(−9)Ω·m).The thermal conductivity of Ag–C@Ti_(3)AlC_(2) reached a maximum value of 135.5 W·m^(−1)·K^(−1) with a 200-nm carbon coating(~1.8 times that of Ag–Ti_(3)AlC_(2)).These results indicate that the carbon-coating method is a feasible strategy for improving the performance of Ag–C@Ti_(3)AlC_(2) composites.

Microstructure and Corrosion Resistance of a Novel AlNiLa Lightweight Medium Entropy Amorphous Alloy Composites

A new type of lightweight AlNiLa medium entropy amorphous alloy composite ribbons(labled as MEAAC ribbons)were prepared by vacuum arc melting technology and high-speed single roller meltspinning method.The microstructure and thermal stability of MEAAC ribbons were examined using X-ray diffraction,differential scanning calorimeter,and scanning electron microscope.Meanwhile,the hardness and surface roughness of these ribbons were measured by Vickers microhardness tester and atomic force microscope.The potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS)were applied to investigate the corrosion behavior of these MEAAC ribbons in simulated seawater(3.5wt%NaCl corrosive solution)at room temperature.The results demonstrate that AlNiLa MEAAC ribbons in the as-received state are mainly composed of amorphous phase and intermetallic compounds.The hardness values of all melt-spun ribbons are above 310 HV_(0.1).With the increase of Al content,the linear polarization resistances of four various AlNiLa MEAAC ribbons are negligibly different numerically.It is also found that Al_(45)Ni_(27.5)La_(27.5) MEAAC ribbons have the most positive corrosion potential and the smallest corrosion current density at the same time;hence it may be a kind of potential material for metal surface protection in harsh ocean environment.

Microstructure transformation of deformed AZ91D during isothermal holding

In order to understand the thermodynamic properties of deformed AZ91D alloy during isothermal holding, the microstructure characteristics and transformation were investigated. The results present that deformation mainly concentrates on the edge of the chips and billets, especially at the interface of α/β. Microstructure transformation mechanism of deformed AZ91D during holding mainly includes recrystallization, spheroidization and Ostwald ripening. The mechanism was then thermodynamically analyzed. During the heating and isothermal holding process, recrystallization driven by residual energy within the deformed AZ91D alloy, spheroidization and Ostwald ripening induced by the reduction of interfacial energy, will inevitably and continuously occur with the extension of heating and holding.

Thermally insulating and fire-retardant bio-mimic structural composites with a negative Poisson's ratio for battery protection

Battery safety has attracted considerable attention worldwide due to the rapid development of wearable electronics and the steady increase in the production and use of electric vehicles.As battery failures are often associated with mechanical-thermal coupled behaviors,protective shielding materials with excellent mechanical robustness and flame-retardant properties are highly desired to mitigate thermal runaway.However,most of the thermal insulating materials are not strong enough to protect batteries from mechanical abuse,which is one of the most critical scenarios with catastrophic consequences.Here,inspired by wood,we have developed an effective approach to engineer a hierarchical nanocomposite via self-assembly of calcium silicate hydrate and polyvinyl alcohol polymer chains(referred as CSH wood).The versatile protective material CSH wood demonstrates an unprecedented combination of light weight(0.018 g cm-3),high stiffness(204 MPa in the axial direction),negative Poisson's ratio(-0.15),remarkable toughness(6.67×105 J m-3),superior thermal insulation(0.0204 W m-1 K-1 in the radial direction),and excellent fire retardancy(UL94-V0).When applied as a protective cover or a protective layer within battery packages,the tough CSH wood can resist high-impact load and block heat diffusion to block or delay the spread of fire,therefore significantly reducing the risk of property damage or bodily injuries caused by battery explosions.This work provides new pathways for fabricating advanced thermal insulating materials with large scalability and demonstrates great potential for the protection of electronic devices.