Effects of Additives on the Microstructure and Tribology Performance of Ta-12W Alloy Micro-Arc Oxidation Coating

Oxide ceramic coatings were fabricated on tantalum alloys by micro-arc oxidation (MAO) to improve their hardness and tribological properties. The MAO coatings were manufactured in a mixed silicatephosphate electrolyte containing NaF and/or EDTA (ethylene diamine tetraacetic acid). The surface morphology,cross-sectional view, chemical composition, hardness, and wear performance of the coatings were analysed. As revealed by the scanning electron microscopy, silica-rich nodules appear on the MAO coating obtained in the silicate-phosphate electrolyte, but the formation of nodules is inhibited with NaF and/or EDTA in the electrolyte.Also, they reduce the roughness and improve the compactness of the coatings, which are composed of Ta_(2)O_(5),(Ta, O), and TaO. A thick and hard coating is obtained in the NaF-containing electrolyte, and the tribology performance is effectively improved. With additives, the nodule structure is detached from the coating surface and dissolved in the electrolyte. By using NaF as an electrolyte additive, the abrasion performance of the MAO coating is enhanced by decreasing the nodule structure, increasing the size of micropores, and improving the coating hardness.

High-Energy Lithium-Ion Batteries:Recent Progress and a Promising Future in Applications

It is of great significance to develop clean and new energy sources with high-efficient energy storage technologies,due to the excessive use of fossil energy that has caused severe environmental damage.There is great interest in exploring advanced rechargeable lithium batteries with desirable energy and power capabilities for applications in portable electronics,smart grids,and electric vehicles.In practice,high-capacity and low-cost electrode materials play an important role in sustaining the progresses in lithium-ion batteries.This review aims at giving an account of recent advances on the emerging high-capacity electrode materials and summarizing key barriers and corresponding strategies for the practical viability of these electrode materials.Effective approaches to enhance energy density of lithium-ion batteries are to increase the capacity of electrode materials and the output operation voltage.On account of major bottlenecks of the power lithium-ion battery,authors come up with the concept of integrated battery systems,which will be a promising future for high-energy lithium-ion batteries to improve energy density and alleviate anxiety of electric vehicles.

Corrosion resistance and mechanisms of smart micro-arc oxidation/epoxy resin coatings on AZ31 Mg alloy: Strategic positioning of nanocontainers

Smart micro-arc oxidation(MAO)/epoxy resin(EP) composite coatings were formed on AZ31 magnesium(Mg) alloy. Mesoporous silica nanocontainers(MSN) encapsulated with sodium benzoate(SB) corrosion inhibitors were strategically incorporated in the MAO micropores and in the top EP layer. The influence of the strategic positioning of the nanocontainers on the corrosion protective performance of coating was investigated. The experimental results and analysis indicated that the superior corrosion resistance of the hybrid coating is ascribed to the protection mechanisms of the nanocontainers. This involves two phenomena:(1) the presence of the nanocontainers in the MAO micropores decreased the distance between MSN@SB and the substrate, demonstrating a low admittance value(^5.18 × 10^(-8)Ω^(-1)), and thus exhibiting significant corrosion inhibition and self-healing function;and(2) the addition of nanocontainers in the top EP layer densified the coating via sealing of the inherent defects, and hence the coating maintained higher resistance even after 90 days of immersion(1.13 × 10^(10)Ω cm^(2)).However, the possibility of corrosion inhibitors located away from the substrate transport to the substrate is reduced, reducing its effective utilization rate. This work demonstrates the importance of the positioning of nanocontainers in the coating for enhanced corrosion resistance,and thereby providing a novel perspective for the design of smart protective coatings through regulating the distribution of nanocontainers in the coatings.

Cross-satellite calibration of high-energy electron fluxes measured by FengYun-4A based on Arase observations

We use the High-energy Electron Experiments(HEP)instrument onboard Arase(ERG)to conduct an energy-dependent cross-satellite calibration of electron fluxes measured by the High Energy Particle Detector(HEPD)onboard FengYun-4A(FY-4A)spanning from April 1,2017,to September 30,2019.By tracing the two-dimensional magnetic positions(L,magnetic local time[MLT])of FY-4A at each time,we compare the datasets of the conjugate electron fluxes over the range of 245–894 keV in 6 energy channels for the satellite pair within different sets of L×MLT.The variations in the electron fluxes observed by FY-4A generally agree with the Arase measurements,and the percentages of the ratios of electron flux conjunctions within a factor of 2 are larger than 50%.Compared with Arase,FY-4A systematically overestimates electron fluxes at all 6 energy channels,with the corresponding calibration factors ranging from 0.67 to 0.81.After the cross-satellite calibration,the electron flux conjunctions between FY-4A and Arase show better agreement,with much smaller normalized root mean square errors.Our results provide a valuable reference for the application of FY-4A high-energy electron datasets to in-depth investigations of the Earth’s radiation belt electron dynamics.

Improved Corrosion Behavior of Biodegradable Mg-4Zn-1Mn Alloy Modified by Sr/F co-doped CaP Micro-arc Oxidation Coatings

The Sr/F co-doped CaP(Sr/F-CaP)coatings were prepared by micro-arc oxidation(MAO)under different voltages to modify the microstructure and corrosion behavior of Mg-4Zn-1Mn alloy.The surface and interface characteristics investigated using scanning electron microscopy(SEM)and energy dispersive X-ray spectrometer(EDS)showed that the MAO coatings displayed uneven crater-like holes and tiny cracks under lower voltage,while they exhibited relatively homogeneous crater-like holes without cracks under higher voltage.The thickness of MAO coatings increased with increasing voltage.The corrosion behavior of Mg-4Zn-1Mn alloy was improved by the MAO coatings.The MAO coatings prepared under 450 V and 500 V voltages possessed the best corrosion resistance with regard to the electrochemical corrosion tests and immersion corrosion tests,respectively.The MAO coatings fabricated under 450-500 V could provide a better corrosion protection effect for the substrate.

Surface modification of biomedical magnesium alloy wires by micro-arc oxidation

Magnesium alloy wires were processed by micro-arc oxidation （MAO） in a modified silicate-phosphate composite electrolyte containing hydroxyapatite （HA） nanopowders and NaOH. Effects of NaOH content in the composite electrolyte on the microstructure and properties of the MAO ceramic coatings on magnesium alloy wires were studied. It is found that the arc voltage of magnesium alloy wires in the micro-arc oxidation process is significantly reduced while the oxidation rate is accelerated. Addition of 2 g/L NaOH in the composite electrolyte is a better choice for improving corrosion resistance of magnesium alloy wires. During early simulated body fluids （SBF） immersion, the micro-arc oxidized magnesium alloy wires undergo a slow and stable degradation. After soaking for 28 d, the protective ceramic coating still shows no damage but significant degradation is observed for magnesium alloy wires after immersion for more than 60 d.

Microstructure and mechanical properties of ceramic coatings formed on 6063 aluminium alloy by micro-arc oxidation

The microstructure and mechanical properties of ceramic coatings formed on 6063 aluminium alloy obtained in silicate-,borate- and aluminate-based electrolyte without and with nanoadditive Al2O3 and TiO2 by micro-arc oxidation（MAO） were studied by scanning electron microscopy（SEM）,energy-dispersive X-ray spectroscopy（EDS）,X-ray diffraction（XRD）,microhardness and friction-abrasion tests,respectively.SEM results show that coatings with nanoadditive have less porosities than those without nanoadditive.XRD results reveal that nanoadditive-containing coatings contain more oxides compared with nanoadditive-free coatings in all cases,which are consistent with the EDS analysis.Mechanical properties tests show that nanoadditive Al2O3-containing coatings have higher microhardness values compared with the other coatings obtained in silicate-,borate- and aluminate-based electrolyte.On the other hand,nanoadditive has a positive effect on improving the wearing-resistance of MAO coatings in all cases.Furthermore,the borate-MAO coatings present an inferior anti-wearing property compared with the silicate- and aluminate-MAO coatings for both the nanoadditive-free and nanoadditive-containing coatings.

Effects of high-energy ball milling oxide-doped and varistor ceramic powder on ZnO varistor

ZnO varistor ceramics doped with Bi2O3, Sb2O3, CO2O3, Cr2O3, and MnO2 were prepared separately by two high-energy ball milling processes： oxide-doped and varistor ceramic powder. A comparison in the electrical and microstructural properties of the samples obtained by both methods was made. The best results on these characteristics were achieved through the high-energy ball milling varistor ceramic powder route, obtaining a nonlinear coefficient of 57 and a breakdown field of 617 V/mm at a sintering temperature of 1000 ℃ for 3 h. The samples synthesized by this technique show not only high density value, 95% of the theoretical density, but also a homogeneous microstructure, which compete with those obtained by the high-energy ball milling oxide-doped powder route. With the advantage that the high-energy ball milling varistor ceramic powder route can refine grain, increase the driving force of sintering, accelerate the sintering process, and reduce the sintering temperature.

Effects of nano-additive TiO_2 on performance of micro-arc oxidation coatings formed on 6063 aluminum alloy

Ceramic coatings were fabricated on aluminum doped with different concentrations of TiO2 nano-additive. alloy substrates by micro-arc oxidation （MAO） in silicate electrolytes Effects of nano-additive concentration on the structural and mechanical properties of the MAO coatings were analyzed. The results revealed that some nano-particle were incorporated into the resulting coating during the MAO process, while there was a reasonable concentration for the TiO2 nano-additive. With increasing the nano-additive concentration to 3.2 g/L, the adhesion value increased, while mean friction coefficient and mass loss decreased. A further increase of nano-additive deteriorated the adhesion and mean friction coefficient values, which was consistent with the micro-hardness tests.

Corrosion behavior of micro-arc oxidation coating on AZ91D magnesium alloy in NaCl solutions with different concentrations

Ceramic oxide coatings were prepared on AZ91D magnesium alloys in alkaline silicate solution using micro-arc oxidation（MAO） technique.The corrosion behavior of MAO coating on AZ91D magnesium alloys in NaCl solutions with different concentrations（0.1%,0.5%,1.0%,3.5% and 5.0% in mass fraction） was evaluated by electrochemical measurements and immersion tests.The results showed that the corrosion rate of the MAO coated AZ91D increased with increasing chloride ion concentration.The main form of corrosion failure was localized corrosion for the MAO coated AZ91D immersed in higher concentration NaCl solutions（1.0%,3.5% and 5.0%）,while it was general corrosion in dilute NaCl solutions（0.1% and 0.5%）.Two different stages of the failure process of the MAO coated AZ91D could be identified：1） occurrence of the metastable pits and 2） growth of the pits.Different equivalent circuits were also proposed based on the results of electrochemical impedance spectroscopy（EIS） for the MAO coated AZ91D immersed in different concentrations of NaCl solutions for 120 h.

Optimization of dual electrolyte and characteristic of micro-arc oxidation coating fabricated on ZK60 Mg alloy

Micro-arc oxidation （MAO） process was carried out in a dual electrolyte system of NaAlO 2 and Na 3 PO 4 to develop compact, smooth and corrosion-resistant coatings on ZK60 Mg alloy by single factor experiments. The microstructural characteristics of coatings were investigated by X-ray diffractometry （XRD） and scanning electron microscopy （SEM） coupled with energy dispersive X-ray spectroscopy （EDS）. Test of mass loss was conducted at a 3.5% NaCl solution to assess the resistance to corrosion. The effect of every element in the dual electrolyte system on voltage—time responses during MAO process and the coating characteristic were also analyzed and discussed systematically via single factor experiments. The results reveal that the main components of NaAlO 2 and Na 3 PO 4 as well as additives of NaOH, NaB4O7 and C6H5Na3O7 demonstrate different effects on MAO process and coating characteristics. By means of single factor experiments, an optimized dual electrolyte system was developed, containing 17.5 g/L NaAlO 2, 5.0 g/LNa3 PO4, 5.0 g/L NaOH, 3.0 g/L NaB4O7 and 4.2g/LC6H5Na3O7 .

Preparation and characterization of ZrO_2/TiO_2 composite photocatalytic film by micro-arc oxidation

ZrO2/TiO2 composite photocatalytic film was produced on the pure titanium substrate using in-situ Zr（OH）4 colloidal particle by the micro-arc oxidation technique and characterized by scanning electron microscope （SEM）, energy dispersive X-ray （EDX）, X-ray diffraction （XRD） and ultraviolet-visible （UV-Vis） spectrophotometer. The composite film shows a lamellar and porous structure which consists of anatase, futile and ZrO2 phases. The optical absorption edge of film is shifted to longer wavelength when ZrO2 is introduced to TiO2. Furthermore, the photocatalytic reaction rate constants of degradation of rhodamine B solution with ZrO2/TiO2 composite film and pure TiO2 film under ultraviolet irradiation are measured as 0.0442 and 0.0186 h 1, respectively.

Preparation and osteoinduction of active micro-arc oxidation films on Ti-3Zr-2Sn-3Mo-25Nb alloy

A layer of porous film containing Ca and P was prepared by the micro-arc oxidation method on the surface of a novel near β biomedical Ti-3Zr-2Sn-3Mo-25Nb alloy, and then NH2- active group was introduced to the films by activation treatment. The phase composition, surface micro-topography and elemental characteristics of the micro-arc oxidation films were investigated with XRD, SEM, EDS and XPS, and the osteoinduction of the micro-arc oxidation films was tested using the simulated body fluid immersion, the in-vitro osteoblast cultivation test and animal experiment. The results show that the oxide layer is a kind of porous ceramic intermixture and contains Ca and P. The films in the simulated body fluid can induce apatite formation, resulting in excellent bioactivity. The cell test discovers that osteoblasts can grow well on the surface of micro-arc oxidation films. And the Ti-3Zr-2Sn-3Mo-25Nb biomedical alloy coated with active porous calcium-phosphate films shows better osteoinduction in vivo.

Structure and corrosion resistance of modified micro-arc oxidation coating on AZ31B magnesium alloy

A hydrophobic surface was fabricated on a micro-arc oxidation (MAO) treated AZ31 Mg alloys via surface modification with myristic acid. The effects of modification time on the wettability of the coatings were investigated using the contact angle measuring device. The surface morphologies and structure of the coatings were evaluated using SEM, XRD and FT-IR. The corrosion resistance was investigated by potentiodynamic polarization curves and long-term immersion test. The results showed that the water contact angle (CA) increases gradually with modification time from 0 to 5 h, the highest CA reaches 138° after being modified for 5 h, and the number and size of the micro pores are decreased. The modification method hardly alters crystalline structure of the MAO coating, but improves the corrosion resistance based on the much positive potential and low current density. Moreover, the corrosion resistance and hydrophobicity can be enhanced with increasing the alkyl chain. The wetting and spreading for the alkylcarboxylate with low surface energy become easier on the micro-porous surface, and alkylcarboxylate monolayer will be formed through bidentate bonding, which changes the surface micropores to a sealing or semi-sealing structure and makes the MAO coating dense and hydrophobic. All the results demonstrate that the modification process improves the corrosion protection ability of the MAO coating on AZ31B Mg alloy.

Preparation and performance of coating on rare-earth compounds-immersed magnesium alloy by micro-arc oxidation

A composite ceramic coating containing Y2O3-ZrO2-MgO（YSZ-MgO） was prepared on AZ91D magnesium alloy,which was immersed in Y（NO3）3 aqueous solution as pretreatment,by micro-arc oxidation（MAO） process.The morphology,elemental and phase compositions,corrosion behavior and thermal stability of the coatings were studied by SEM,EDX,XRD,electrochemical corrosion test,high temperature oxidation and thermal shock test.The results show that the coating mainly consists of ZrO2,Y2O3,MgO,Mg2SiO4,and MgF2.Among these compounds,Y2O3 accounts for 26.7% of（Y2O3 ＋ ZrO2）.The thickness of YSZ-MgO coating is smaller than that of ZrO2-MgO coating,but its compactness and surface roughness are better than those of ZrO2-MgO coating.YSZ-MgO coating has a good corrosion resistance,and its corrosion rate in 5% NaCl aqueous solution is lower than that of ZrO2-MgO and only about 8.5% of that of AZ91D magnesium alloy.After oxidation at 410 °C,the mass gain of AZ91D magnesium alloy presents a linear increase with the oxidation time.The YSZ-MgO coating and ZrO2-MgO coating can remarkably decrease the oxidation mass gain.The oxidation mass gain of YSZ-MgO coating is lower than that of ZrO2-MgO coating,especially during a long oxidation period.The thermal shock resistance of YSZ-MgO coating is superior to ZrO2-MgO coating.

Preparation and wear properties of TiB_2/Al-30Si composites via in-situ melt reactions under high-energy ultrasonic field

TiB2/Al-30Si composites were fabricated via in-situ melt reaction under high-energy ultrasonic field. The microstructure and wear properties of the composite were investigated by XRD, SEM and dry sliding testing. The results indicate that TiB2 reinforcement particles are uniformly distributed in the aluminum matrix under high-energy ultrasonic field. The morphology of the TiB2 particles is in circle-shape or quadrangle-shape, and the size of the particles is 0.1-1.5μm. The primary silicon particles are in quadrangle-shape and the average size of them is about 10μm. Hardness values of the Al-30Si matrix alloy and the TiB2/Al-30Si composites considerably increase as the high energy ultrasonic power increases. In particular, the maximum hardness value of the in-situ composites is about 1.3 times as high as that of the matrix alloy when the ultrasonic power is 1.2 kW, reaching 412 MPa. Meanwhile, the wear resistance of the in-situ TiB2/Al-30Si composites prepared under high-energy ultrasonic field is obviously improved and is insensitive to the applied loads of the dry sliding testing.

Accelerated intermetallic phase amorphization in a Mg-based high-entropy alloy powder

We describe a novel mechanism for the synthesis of a stable high-entropy alloy powder from an otherwise immiscible Mg-Ti rich metallic mixture by employing high-energy mechanical milling.The presented methodology expedites the synthesis of amorphous alloy powder by strategically injecting entropic disorder through the inclusion of multi-principal elements in the alloy composition.Predictions from first principles and materials theory corroborate the results from microscopic characterizations that reveal a transition of the amorphous phase from a precursor intermetallic structure.This transformation,characterized by the emergence of antisite disorder,lattice expansion,and the presence of nanograin boundaries,signifies a departure from the precursor intermetallic structure.Additionally,this phase transformation is accelerated by the presence of multiple principal elements that induce severe lattice distortion and a higher configurational entropy.The atomic size mismatch of the dissimilar elements present in the alloy produces a stable amorphous phase that resists reverting to an ordered lattice even on annealing.

A compact X-band backward traveling-wave accelerating structure

Very high-energy electrons(VHEEs)are potential candidates for FLASH radiotherapy for deep-seated tumors.We proposed a compact VHEE facility based on an X-band high-gradient high-power technique.In this study,we investigated and realized the first X-band backward traveling-wave(BTW)accelerating structure as the buncher for a VHEE facility.A method for calculating the parameters of single cell from the field distribution was introduced to simplify the design of the BTW structure.Time-domain circuit equations were applied to calculate the transient beam parameters of the buncher in the unsteady state.A prototype of the BTW structure with a thermionic cathode-diode electron gun was designed,fabricated,and tested at high power at the Tsinghua X-band high-power test stand.The structure successfully operated with 5-MW microwave pulses from the pulse compressor and outputted electron bunches with an energy of 8 MeV and a pulsed current of 108 mA.

Strategies to achieve effective nitrogen activation

Ammonia serves as a crucial chemical raw material and hydrogen energy carrier.Aqueous electrocatalytic nitrogen reduction reaction(NRR),powered by renewable energy,has attracted tremendous interest during the past few years.Although some achievements have been revealed in aqueous NRR,significant challenges have also been identified.The activity and selectivity are fundamentally limited by nitrogen activation and competitive hydrogen evolution.This review focuses on the hurdles of nitrogen activation and delves into complementary strategies,including materials design and system optimization(reactor,electrolyte,and mediator).Then,it introduces advanced interdisciplinary technologies that have recently emerged for nitrogen activation using high-energy physics such as plasma and triboelectrification.With a better understanding of the corresponding reaction mechanisms in the coming years,these technologies have the potential to be extended in further applications.This review provides further insight into the reaction mechanisms of selectivity and stability of different reaction systems.We then recommend a rigorous and detailed protocol for investigating NRR performance and also highlight several potential research directions in this exciting field,coupling with advanced interdisciplinary applications,in situ/operando characterizations,and theoretical calculations.

Bimodal-grained Ti fabricated by high-energy ball milling and spark plasma sintering

Bimodal-grained Ti containing coarse and fine grains was fabricated by high-energy ball milling and spark plasma sintering (SPS). The microstructure and mechanical properties of the compacts sintered by Ti powders ball-milled for different time were studied. Experimental results indicated that when the ball-milling time increased, the microstructure of sintered Ti was firstly changed from coarse-grained to bimodal-grained structure, subsequently transformed to a homogeneous fine-grained structure. Compared with coarse-grained Ti and fine-grained Ti, bimodal-grained Ti exhibited balanced strength and ductility. The sample sintered from Ti powders ball-milled for 10 h consisting of 65.3% (volume fraction) fine-grained region (average grain size 1 μm) and 34.7% coarse-grained region (grain size > 5 μm) exhibited a compress strength of 1028 MPa as well as a plastic strain to failure of 22%.