Effect of porosity and interface structures on thermal and mechanical properties of SiC_p/6061Al composites with high volume fraction of SiC

50 vol.% SiCp/Al composites with high thermal and mechanical properties were successfully produced by spark plasma sintering technique. The influences of sintering temperature on the thermal conductivity, coefficient of thermal expansion and bending strength of the SiCp/Al composites were carefully investigated. The results show that the SiCp/Al composites sintered at 520℃ exhibits a thermal conductivity of 189 W/(m·K), a coefficient of thermal expansion (50.200℃) of 10.03×10^-6 K^-1 and a bending strength of 649 MPa. The high thermal and mechanical properties can be ascribed to the nearly full density and the well interfacial bonding between the alloy matrix and the SiC particles. This work provides a promising pathway for producing materials to meet the needs of high performance electronic packaging.

Nanosized copper powders prepared by gel-casting method and their application in lubricating oil

Nanosized copper powders were prepared by a gel-casting method using copper nitrate, acrylamide（AM） and N, N′-methylenebisacrylamide（MBAM） as the main raw materials. The as-prepared copper powders were characterized by X-ray diffractometry and scanning electron microscopy, and then added into a 48# industrial white oil. Dispersion and wear properties of the compounded lubricating oil were tested. The results show that the copper powders prepared are of high purity, fine dispersibility with mean particle size of about 60 nm and with a narrow particle size distribution. The nanosized copper powders can be well dispersed in the lubricating oil. The addition of the copper powders obviously improves the anti-wear properties of the lubricating oil owing to their good self-repairing performance. Compared with 48# industrial white lubricating oil, the friction coefficient of GCr15 steel with the compounded oil containing 0.6% copper powders reduces by 0.07 and nearly no wear chippings are found in the scratches of the friction counter parts.

Microstructure and thermal stability of sintered pure tungsten processed by multiple direction compression

Multiple direction compression(MDC)was conducted on sintered pure tungsten(99.9%,mass fraction)with different reductions at 1423 K.The microstructure,microhardness and thermal stability of the MDC-processed samples were studied by X-ray diffraction(XRD),electron backscattered diffraction(EBSD)and differential scanning calorimetry(DSC)compared with those of the initial sintered tungsten.The results show that the dislocation density increases significantly with the reduction of MDC,ranging from 3.08×1014 m-2 for the initial sintered tungsten to 8.08×1014 m-2 for the tungsten after MDC with the reduction of 50%.The average grain size decreases from 83.8 to 14.7μm and the microhardness value increases from HV0.2 417 to HV0.2 521.The recrystallization temperature for the tungsten samples processed by MDC is approximately constant at around 1600 K.The MDC of sintered tungsten results in a decrease of grain size concurrent with an increase of uniformly distributed nucleation sites,which leads to the improvement of the thermal stability.

Structure and tribological properties of Si/a-C:H(Ag)multilayer film in stimulated body fluid

Si/a-C:H(Ag)multilayer films with different modulation periods are prepared to test their potential applications in human body.The composition,microstructure,mechanical and tribological properties in the simulated body fluid are investigated.The results show the concentration of Ag first decreases and then increases with the modulation period decreasing from 984 nm to 250 nm.Whereas the C content has an opposite variation trend.Notably,the concentration of Ag plays a more important role than the modulation period in the properties of the multilayer film.The a-C:H sublayer of the film with an appropriate Ag concentration(8.97 at.%)(modulation period of 512 nm)maintains the highest sp3/sp2 ratio,surface roughness and hardness,and excellent tribological property in the stimulated body fluid.An appropriate number of Ag atoms and size of Ag atom allow the Ag atoms to easily enter into the contact interface for load bearing and lubricating.This work proves that the Ag nanoparticles in the a-C:H sublayer plays a more important role in the tribological properties of the composite-multilayer film in stimulated body fluid condition.

Anti-oxidation characteristics of Cr-coating on surface of Ti-45Al-8.5Nb alloy by plasma surface metallurgy technique

TiAl-based alloys have received extensive attention recently due to their excellent properties. However, the weak oxidation resistance at temperatures higher than 800℃ can limit their further high-temperature structural applications.To improve the oxidation resistance of a high-Nb-content γ-TiAl alloy(Ti-45 Al-8.5 Nb, in units of at.%), a chromium(Cr)coating is prepared by using the plasma surface alloying technique, separately, at 800℃ and 1000℃. The x-ray diffraction(XRD) patterns reveal that an oxide surface layer consisting of Cr2O3, Al2O3, and TiO2 is produced on the Cr-coated Nb containing γ-TiAl substrates during the initial oxidation. However, the Cr2O3 is dominated in the oxide surface layer after being isothermally oxidized for 300 h. The oxidation kinetic curves are composed of a parabolic law stage(≤ 90 h) and a biquadratic law stage(≥ 90 h), fit by weight–gain curves. Due to diffusion in the fabrication process and oxidation process,the Cr-coated specimens have an adhesion force after being isothermally oxidized, specifically 69 N for a specimen after oxidation for 300 h. These results demonstrate that the Cr coating enhances the oxidation resistance and adhesion of a Ti-45 Al-8.5 Nb alloy, which may provide a new feasible scheme for designing oxidation protection layers.

Cryoballoon pulmonary vein isolation and left atrial appendage occlusion prior to atrial septal defect closure: A case report

BACKGROUND In patients who suffer from both atrial fibrillation(AF)and atrial septal defect(ASD),cryoballoon pulmonary vein isolation(PVI),sequential left atrial appendage(LAA)occlusion and ASD closure could be a strategy for effective prevention of stroke and right heart failure.CASE SUMMARY A 65-year-old man was admitted to our institution due to recurrent episodes of palpitations and shortness of breath for 2 years,which had been worsening over the last 48 h.He had a history of AF,ASD,coronary heart disease with stent implantation and diabetes.Physical and laboratory examinations showed no abnormalities.The score of CHA2DS2VASc was 3,and HAS-BLED was 1.Echocardiography revealed a 25-mm secundum ASD.Pulmonary vein(PV)and LAA anatomy were assessed by cardiac computed tomography.PV mapping with 10-pole Lasso catheter was performed following ablation of all four PVs with complete PVI.Following the cryoballoon PVI,the patient underwent LAA occlusion under transesophageal echocardiographic monitoring.Lastly,a 34-mm JIYI ASD occlude device was implanted.A follow-up transesophageal echocardiography at 3 mo showed proper position of both devices and neither thrombi nor leakage was found.CONCLUSION Sequential cryoballoon PVI and LAA occlusion prior to ASD closure can be performed safely in AF patients with ASD.

Microstructures and properties of Cu/Ag(Invar) composites fabricated by powder metallurgy

The Ag(Invar)composite powder prepared by ball milling was used to fabricate the Cu/Ag(Invar)composites.Microstructures and properties of the composites were studied after sintering and thermo-mechanical treatment.The results indicatethat during ball milling,micro-forging weld and work-hardening fracture result in that the average particle size of the Ag(Invar)powder increases rapidly at first,and then decreases sharply,finally tends to be constant.Compared with the Cu/Invar ones,thesinterability of the composites is greatly improved,resulting in that the pores in them are smaller in amount and size.After thethermo-mechanical treatment,the Cu/Ag(Invar)composites are nearly fully dense with the optimum phase composition and elementdistribution.More importantly,Cu and the Invar alloy in the composites distribute continuously in a three-dimensional(3D)networkstructure.Cu/Invar interface diffusion is effectively inhibited by the Ag barrier layer,leading to a great improvement of themechanical and thermal properties of the Cu/Ag(Invar)composites.

Train probe for beam diagnostics of the SC200 superconducting cyclotron

The SC200 proton therapy system commissioned by the Hefei CAS Ion Medical and Technical Devices Co.,Ltd.(HFCIM;Hefei,China)and the Joint Institute for Nuclear Research(JINR;Dubna,Russia)has made significant progress.A main radial beam diagnostic system(MRBDS)equipped with a new type of train probe was developed to satisfy the requirements of beam diagnosis.In this paper,the detailed design of the mechanical structure and electronics system of the MRBDS is presented.The electronics system,which includes hardware and software components,was tested and calibrated.The results show that measurement errors can be significantly reduced by the designed calibration procedures.The repeatability of the mechanical structure was also verified,and the experimental results indicate that the unidirectional repeatability of the positioning is better than 0.3 mm.Finally,the MRBDS was used to measure the phase lag of the particles in the beam,and the results showed a high degree of agreement with theoretical calculations,which proved the applicability and high efficiency of the MRBDS.

Chloride Assisted Growth of Aluminum Nitride Nanobelts and Their Enhanced Dielectric Responses

Aluminum nitride （AlN） nanobelts were successfully synthesized in high yield through a chloride assisted vapor-solid process. X-ray diffraction, transmission electron microscopy, and selected area electronic diffraction demonstrate that the as-prepared nanobelts are pure, structurally uniform and single crystalline, and can be indexed to hexagonal wurtzite structure. The micro observations show that there exist no defects in the obtained nanobelts. The growth direction of the nanobelts is along [0001]. The frequency spectra of the relative dielectric constant and of the dielectric loss were measured in the frequency range of 50 Hz to 5 MHz. Analysis of these spectra indicates that the interface in samples has great influence on the dielectric behavior of samples. As compared with AlN micropowders, AlN nanobelts have much higher relative dielectric constant, especially at low frequencies at room temperature.

Integration of urchin-like MnCo_(2)O_(4)@C core–shell nanowire arrays within porous copper current collector for superior performance Li-ion battery anodes

Spinel MnCo_(2)O_(4) is a promising energy storage candidate as anode materials in lithium-ion batteries owing to synergistic effects of two intrinsic solid-state redox couples.However,low conductivity,poor rate capacity and rapid capacity fading have seriously impaired its practical applications.To overcome the inferiorities,urchin-like MnCo_(2)O_(4)@C core–shell nanowire arrays have been fabricated directly within a porous copper current collector via a facile hydrothermal method followed by a chemical vapor deposition carbonization process.In a typical nanowire,the core is composed of interconnected MnCo_(2)O_(4)nanoparticles and the shell shows as a thin amorphous carbon layer.The integrated MnCo_(2)O_(4)@C/Cu structure could act as working anodes without using additives or polymer binders.While MnCo_(2)O_(4)@C/Cu possesses slightly longer Li-ion insertion/desertion pathway than that of MnCo_(2)O_(4)/Cu,the carbon shell could effectively prevent the pulverization of MnCo_(2)O_(4) and lower down charge transfer resistance and actively participate in Li-ion cycles.The rearrangement of carbon atoms during lithiation/delithiation cycling could inhibit the formation of passive solid electrolyte interphase films.As a result,the MnCo_(2)O_(4)@C/Cu electrode presents superior rate capacity(600 mAh·g^(−1) at 1 A·g^(−1)) and better stability(797 mAh·g^(−1) after 200 cycles at 100 mA·g^(−1)).The excellent reversible Li ion storage capacity,cycling stability and rate capacity endow MnCo_(2)O_(4)@C/Cu great potential as stable and high output integrated anode materials in Li-ion batteries.

Tailoring strength and ductility of high-entropy CrMnFeCoNi alloy by adding Al

High-entropy alloys with high strength and acceptable ductility at both room and elevated temperatures for high-temperature structural applications are desired. In this paper, CrMnFeCoNi alloy with outstanding ductility but low strength was selected as baseline alloy to study the formation of hard phase to strengthen this ductile alloy by adding Al into it. The results indicate that there is a phase structure transition from fcc to bcc when adding enough Al into CrMnFeCoNi. The yield strength and hardness increase with the content of Al increasing, due to the formation of hard bcc phase in the ductile CrMnFeCoNi alloy.The CrMnFeCoNiAl alloy with a bcc structure shows a high yield strength and adequate ductility at elevated temperatures. At 400 and 500℃, the yield strength and ductility of CrMnFeCoNiAl alloy are 975.59 MPa and6.39%and 989.48 MPa and 9.15%, respectively. An example of tailoring the strength and ductility of high-entropy alloy is demonstrated in this paper.

One-pot synthesis of nickel-cobalt hydroxyfluorides nanowires with ultrahigh energy density for an asymmetric supercapacitor

A novel and unique nickel-cobalt hydroxyfluorides(NiCo-HF)nanowires material is fabricated by one-pot solvothermal synthesis method for asymmetric supercapacitor.The synthesis mechanism and factors that influence the formation of the Ni Co-HF nanowires have been further discussed.The as-prepared NiCo-HF electrode exhibits a high specific capacitance of 3,372.6 F g^(à1),and the capacitance retention of 94.3%can be achieved at a high current density of 20 A g^(à1)after 10,000 cycles.The outstanding electrochemical performance of the electrode can be attributed to the synergistic effect of the nanowires morphology and complicated redox process of active material.Furthermore,an asymmetric supercapacitor assembled with Ni Co-HF nanowires as positive electrode and activated carbon as the negative electrode shows an ultrahigh energy density of 83.6 Wh kg^(à1)at a power density of 379.4 W kg^(à1)and an excellent cycling stability with 86.3%capacitance retention after 10,000 cycles,indicating that this novel material has great promise for potential application in energy storage device.

Entropy versus enthalpy in hexagonal-close-packed highentropy alloys

The addition of hexagonal-close-packed(hcp)non-rare-earth elements Zr,Ti and Co,to the 10-component hep rare-earth-based high-entropy alloys(HEAs)with a composition of ScYLaNdGdTbDyHoErLuX(X=Zr,Co and Ti)was investigated.The enthalpy of mixing between elements was found to have a significant effect on the formation of phases.The addition of Co combines with elements that had a strong chemical affinity to form intermetallic compounds by the effect of enthalpy.Ti was added with all elements with poor chemical affinity and exhibited rejection to form a phase alone.These were the two terminal manifestations of the role of enthalpy over entropy.Part of Zr was soluble in the matrix under the action of entropy,while the other part had a greater affinity for Sc than the other elements to form a precipitate under the action of enthalpy.This was the result of the local balance between the effect of enthalpy and entropy.The solid solution of the elements had different degrees of strengthening effect,among which Zr had the most excellent strengthening effect from 185 to 355 MPa,so the solid solution strengthening model and precipitation strengthening model were proposed to predict the strength of the alloy with the addition of Zr effectively.

Effects of different alloying elements M(M=Fe,Ni,Mn,Si,Mo,Cu,Y)on Cr_(2)0_(3)with Cl:a first-principles study

Using the first-principles methods,the effects of different alloying elements M(M=Fe,Ni,Mn,Si,Mo,Cu,Y)on Cr_(2)0_(3)with Cl adsorption are studied.The results show that the layer distance of all doped models has been widened to different degrees with Cl adsorption.When Mo or Y is doped into the passive film,the difference of layer distance is reduced to a certain extent.The interaction between alloying elements and Cl is studied by calculating the adsorption height,bond population and electron density difference.The results show that Mo and Y can inhibit Cl erosion and improve the corrosion resistance of passive film.Furthermore,we investigate the CrMoFe and CrMoY co-doped system with Cl adsorption.The calculations point out that when Mo and Y are doped together in the passive film,the corrosion resistance of the system is more prominent than that of CrMo,CrY and CrMoFe co-doping systems.

Direct chemical vapor deposition growth of graphene on Ni particles using solid carbon sources

Graphene has attained a considerable amount of popularity as an attractive ultra-thin reinforcement for nickel(Ni)matrix composites in recent years.However,its excellent reinforcement efficiency is suffered from the agglomeration of graphene nanosheets in manufacturing process and the poor bonding strength of graphene with Ni matrix.To overcome these two problems,one of the efficient strategies is to in-situ grow graphene reinforcements on Ni particles for powder metallurgy.This work aims to synthesize uniform graphene@Ni composite particles by using polymethyl methacrylate(PMMA)as the solid sources for chemical vapor deposition(CVD)process.The results demonstrate that few-layer or multilayer graphene with different morphologies can be grown on the particles by controlling the PMMA content and annealed temperature,respectively.The optimum condition for the formation of high-quality few-layer graphene is 1.0 mg·ml^(-1) PMMA and 900℃.A competition mechanism rises from the growth kinetic,and the spatial confinement effect has led to the formation of graphene with different microstructures and morphologies.

Microstructure evolutions of the W-TiC composite conducted by dual-effects from thermal shock and He-ion irradiation

Considering that tungsten(W)materials served as the plasma-facing material in the fusion reactor would be exposed to edge-localized modes(ELMs)-like thermal shock loading accompanied with He-ion irradiation,the W-TiC composite produced with a wet-chemical method was conducted by the dual effects from the laser beam thermal shock first and He-ion irradia-tion later in this work.The microstructure changes of the W-TiC composite before and after two tests were characterized by scanning electron microscopy or transmission electron microscopy.After the laser beam thermal shock test,there was an obvious interface on the exposed surface of the W-TiC composite.Several main cracks and melting areas could be found nearby the interface and center,respectively.Furthermore,a mixture of tungsten oxide and TiC was easy to aggregate and form into circle areas surrounding the melting area.The thermal shock tested that W-TiC composite was then subjected to the He-ion irradiation.The typical features of fuzz structures could be detected on the surface of the W-TiC composite apart from the center of the melting area.Notably,several nano-sized He bubbles deeply distributed at grain boundaries in the melting area,owing to the grain boundary functioning as the free path for He diffusion.

Preface to the special issue:applications of tungsten materials

Tungsten(W)and its alloys/compounds possesses several proprietary features,which are applied widely in the fields of defense and military,aerospace,electronic industry,radiation shield,machining,photoelectricity,catalytic and energy,etc.Topics in this special issue contain six contributions with two review papers and four research articles,covering plasma facing materials(PFMs)of W materials in fusion engineering,hardmetals of tungsten carbide(WC)-based composites in machining and electrochromic functional materials of tungsten oxide(WO3)in smart materials.