- Ei，ESCI收录期刊
- 中国科学引文数据库(CSCD)核心期刊
- 中文核心期刊
- 文摘与引文数据库(Scopus)
- 剑桥科学文摘(CSA)
Graphite anode slurry of lithium-ion flow battery was prepared by the method of ball milling. The morphology, conductivity, specific capacity and cycle performance of graphite anode slurry were studied. Results show that the addition of conductive carbon material can improve the suspension stability of the electrode slurry; the ball milling process can not only improve the suspension stability but also reduce the resistivity of the mixed powders of graphite and conductive carbon materials, the ball milling effect is satisfactory when the mass ratio of the balls and the solid particles is 5:1, but too high ratio of the milling ball and the solid materials can destroy the layer structure of the graphite and affect the stability of the slurry. Increasing the fraction of the graphite and conductive carbon materials can form stable electrical network structure in the slurry and improve the reversible capacity; at the premise of keeping the flowability of the electrode slurry, the reversible specific capacity can be more than 40mAh/g. The capacity loss of graphite anode slurry mainly occurs in the first charging-discharging process, as the increase of the cycles, the capacity loss rate decreases, the capacity goes stable after 5 cycles.
Micro layer of GO was obtained by micro adjustment and control. LiFePO4/graphene composite cathode materials were synthesized using a spray drying followed by high temperature reduction modification method, to improve conductivity of LiFePO4 with excellent conductivity of graphene. The structure, morphology and electrochemical performance of the composite materials were characterized by XRD, FTIR, SEM, TEM and electrochemical measurement technologies. The three-dimensional conductive network was constructed by graphene composite in material particles, which can improve the charge transfer rate of the interface of electrolyte/electrode materials and the electrochemical performance of LiFePO4. The results show that the discharge specific capacity of LiFePO4 without graphene is only 155mAh/g, while the discharge specific capacity of LiFePO4/graphene is 164mAh/g at 0.1C.The discharge specific capacity of LiFePO4/graphene is 140, 119mAh/g at 1, 2C, respectively.
In order to prepare highly efficient and environmentally friendly photocatalysts, polyvinyl alcohol nanofibers coated with Al-doped ZnO precursor (AZO) were prepared via electrospinning and hydrothermal synthesis. Furthermore, AZO hollow nanofibers were successfully fabricated after calcination at high temperature. The morphology, structure and properties of the samples were characterized by scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectrometer, thermogravimetric analyzer and UV spectrophotometer. The results show that AZO hollow nanofibers have good photocatalytic degradation of dye.
The polyborosilazane aerogels were prepared by hydrosilylation reaction using polyborosilazane as raw material with divinylbenzeneas crosslinking agent, and then dried by CO2 supercritical drying. Infrared spectroscopy, scanning electron microscopy, specific surface area and aperture analyzer, contact angle measurement were used to characterize the formation, microstructure and hydrophobic property of polyborosilazane aerogels. The results show that the polyborosilazane aerogels are prepared by hydrosilylation reaction using polyborosilazane with divinylbenzene; the specific surface areas of the resultant aerogels with three-dimensional network structure are in the range of 307-458cm2/g, which is a mesoporous material with superhydrophobic property. The pore volume is in the range of 1.20-2.17cm3/g and pore size is in the range of 2.0-100nm, and when the volume fraction of the starting solvent is 85%, the hydrophobic performance of polyborosilazane aerogels is the best, the water contact angle is 151.5°.
The pure Nb powder, Si powder or Nb5Si3 powder were used as raw materials and three kinds of Nb-16Si binary alloys were fabricated by laser melting deposition (LMD) via the method of powder preplaced and coaxial powder feeding, respectively. The microstructure and micro-hardness of these alloys were investigated with SEM, EDS and XRD, etc. The results show that these Nb-16Si alloys prepared by LMD consist of NbSS and Nb3Si phases. The microstructure of these alloys is influenced by the feeding method and chemical state of the raw powder strongly. The Nb-16Si alloy fabricated by powder preplaced method with the pure element powder as raw materials is composed of dendritic primary NbSS with the size of 1-5μm and NbSS/Nb3Si eutectic structure and the Vickers micro-hardness of the alloy is about 773HV. Using the method of dual-channel coaxial powder feeding can make the microstructure of the Nb-16Si alloy finer and more homogeneous. The primary NbSS in this alloy is uniformly distributed with nearly equiaxed shape, the average size is only 2μm and its micro-hardness is increased to 817HV. The microstructure of the Nb-16Si alloy prepared by dual-channel coaxial powder feeding method with pure Nb and Nb5Si3 as raw powder exhibits pseudoeutectic structure, the micro-hardness reaches 907HV.
The grain orientation and the interface character distribution were investigated for γ precipitation from the supersaturated α during aging at 1323K in duplex stainless steel by using EBSD technique and misorientation analysis based on Rodrigues-Frank (R-F) space. The results show that sharp texture and the grain boundary character distribution featured by a high population of low angle grain boundary (LAB) and a small number of twin boundaries (TBs) are produced in the γ precipitated from cold-rolled supersaturated coarse α with pre-strain of ε=2. The precipitated γ grains approximately possess K-S, N-W and Bain orientation relationship with the α matrix equally. For the unstrained α matrix of the same orientation, nearly random texture and the grain boundary character predominated by TBs are introduced in the γ precipitation after aging. Most of γ have K-S relation with the α matrix. However, twining in γ leads to the deviation from typical K-S orientation relationship. And also, one-fourth of phase boundaries along γ grains containing twins are found to obey a new orientation relationship of 35°/〈110〉 with α matrix.
The superfine fiber of thermoplastic polyimide(LPI), whose average diameter ranges from 0.36μm to 1.47μm, was prepared through electrospinning with DMAc as solvent. It lays a good foundation for the mass preparation of LPI non-woven. The influence of electrospinning process conditions, including LPI concentration, flow rate and voltage, on morphology of LPI fiber was investigated systematically. The results show that the average diameter increases and the fibers diameter distribution turns wider with the LPI concentration increasing from 22%(mass fraction, same as below) to 30%. Meanwhile, when the concentration is rather lower, some cambiform fibers can be observed. As the concentration increases, the cambiform fiber disappears. While the concentration increases continually, the fibers are adhered to be flakiness. The change of the spinning voltage makes little difference on the average diameter of fibers; the average diameter of fibers increases with the increase of the flow rate of LPI solution; when the flow rate is more than 1.5mL/h, the fibers start to be adhered, the cambiform fibers appear while the flow rate is over 1.8mL/h. Through optimizing the process, the LPI fibers with average diameter of 1.18μm were prepared under 30℃ with the conditions of 28% concentration, 15kV voltage, 1.2mL/h flow rate and the 25cm receiving distance.
Based on the analysis on temperature and stress distributions, as well as fatigue crack propagation in cutting tools, a model for designing compositional distribution and microstructure with graded characteristics was proposed. The addition of ductile phase and the introduction of the graded structure are beneficial to slow down the fatigue crack propagation rate and improve tool life.Al2O3-(W, Ti)C-TiN-Mo-Ni nano-composite tool material with graded structures was fabricated via two stage hot pressing sintering process, and the microstructure and mechanical properties were studied. The results show that the surface hardness, fracture toughness of inner layer and bending strength of the cermet with sintered gradient structure reach 19.258GPa, 10.015MPa·m1/2 and 1017.475MPa, respectively.The performance requirements to cutting tools were met. The dimple cleavage and torn edge of the binding phase in the fracture surfaces can be beneficial to the improvement of the fracture toughness and bending strength, so the resistance to fatigue crack propagation of tools is improved.
The study involves in-situ synthesis of CrFeAlTi composite coating using laser micro-melting processing. The coating was successfully prepared by laser irradiating CrFeAlTi coating prepared by flame spraying on the China low activation martensitic (CLAM) steel substrate, and then Al2O3-TiO2 composite ceramic coating was synthesized by in-situ reaction on the surface of flame sprayed coating. The coating morphology, microstructure, phase composition, micro-hardness, dry sliding wear properties and corrosion resistance in liquid PbBi alloy were analyzed by stereomicroscope, scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), micro-sclerometer, vertical universal friction wear testing machine and static PbBi corrosion test device, respectively. The test results show that the surface of Al2O3-TiO2 composite ceramic coating is smooth, and the microstructure of coating is both homogeneous and dense without defects such as crack, dimple and porosity, etc., a good metallurgical bonding between the composite ceramic coating and the substrate, and the interface is obvious. The phases of the coating surface are mainly composed of Al2O3, TiO2, (Al.948Cr.052)2O3, Fe2TiO5 and FeCr, etc. The coating shows a high average micro-hardness of approximately 1864.2HV0.2, which is about three times higher than that of the CLAM steel substrate, and presents gradient distribution with stable transition from the coating surface to the substrate. Comparing with the substrate, the coating presents excellent wear resistance. The wear mass loss of the coating is just one sixth of that of the substrate. Meanwhile, the coating exhibits the best corrosion resistance in the liquid PbBi.
The lower surface of bamboo leaves was adopted as a hydrophobic surface master. Regarding the characteristics of electroforming for hydrophobic surfaces, a wet-out treatment and a cathode horizontal-rotation were adopted to improve the replication quality of micro-nano hierarchical structures. The results show that the wet-out treatment can effectively improve the nickel ion deposition in the micro-nano cavities. The cathode horizontal-rotation is proved to be helpful for the better macro-and micro-qualities of electroformed nickel mold inserts. Electroforming technology with the wet-out treatment and the cathode horizontal-rotation can significantly improve the replication quality of micro-nano hierarchical structures of bamboo leaf surfaces, and can be used to successfully fabricate the hydrophobic nickel mold inserts with high quality for further molding.
Mo-Si-B coating was prepared on Nb-Si alloys to improve the high-temperature oxidation. The influence of the halide activators (NaF and AlF3) on Si-B co-depositing to obtain Mo-Si-B coating on Nb-Si alloys was analyzed by thermochemical calculations. The results show that NaF proves to be more suitable than AlF3 to co-deposit Si and B. Then Mo-Si-B can be coated on Nb-Si based alloys using detonation gun spraying of Mo followed by Si and B co-deposition. The fabricated coatings consist of outer MoSi2 layer with fine boride phase and inner unreacted Mo layer. The mass gain of the Mo-Si-B coating is 1.52mg/cm2 after oxidation at 1250℃ for 100h. The good oxidation resistance results in a protective borosilicate scale formed on the coating.
To reveal the mechanical properties of thermal spray coating on different scales, flame spray NiCrBSi coating with average thickness 750μm was prepared on 45 carbon steel substrate, the mechanical properties, elastic-plasticity and indentation deformation of coating surface and cross-section were studied by nanoindentation. Results indicate that scale-dependent behaviors of coating mechanical properties were observed as a function of indentation depth for either the coating surface or the cross-section. The nano hardness, modulus and elastic-plasticity of coating decrease with the increasing indentation depth. The coating surface exhibits higher elasticity than the coating cross-section, the ratio of elastic work to the total indentation work, ηIT, of coating surface is 52% at the depth of 500nm, while that of coating cross-section is 40%; moreover, the coating cross-section possesses higher hardness and modulus than the coating surface; the corresponding values of the coating crosssection are 28% and 33% at the depth of 2000nm, higher than those of the coating surface, respectively. The indentation marks show ideal plastic deformation, pile-up and sink-in, and cracks. The difference of ηIT values between coating surface and cross-section decreases with the increasing indentation depth. It reaches about 35% at the depth of 2500nm from the both coating directions. For the coating splat structure, hardness and elastic modulus are the same in different directions, besides, with the increasing indentation depth, larger volume is involved in the indentation. The influence of the surrounding splats (especially the pores, cracks or grain/splat boundaries) on the measured coating properties is enhanced gradually, leading to differences in the appearance between different coating directions, as well as the decrease of coating hardness, elastic modulus.
Micro-arc oxidation (MAO) ceramic coatings were prepared on Ti2AlNb alloy in silicate/phosphate electrolytes with different concentrations of Na2WO4. The influence of Na2WO4 on the coating growth process, coating structure and composition was analyzed by SEM, XRD and XPS. The tribological behavior of MAO coatings was evaluated by the ball-disc wear test. The results show that the growth rate of MAO coating in electrolyte without Na2WO4 is only 0.08μm/min, meanwhile, the coating is loose and rough, and "networks" connecting with big pores exist on the coating surface.The main phase compositions of this coating are rutile TiO2, anatase TiO2, Al2O3, and Nb2O5. The addition of Na2WO4 in the electrolyte shortens the time before sparking of Ti2AlNb alloy, increases the growth rate of the coating, improves the uniformity of coating and meanwhile, a small amount of WO3 is introduced in the coating. Besides, MAO coatings formed in the participation of Na2WO4 have better wear resistance. Severe abrasive wear occurs when the test is made on Ti2AlNb alloy with Si3N4, the friction coefficient reaches 0.5-0.7. Both the friction coefficient and wear rate decrease obviously when Ti2AlNb is treated by MAO. The friction coefficient and wear rate of MAO coating prepared in the electrolyte with 4g/L Na2WO4 are 0.24 and 6.2×10-4mm3/(N·m), respectively. Only "fish scales" caused by fatigue wear appears on the coating surface.
The aluminized 45 and H13 steel were prepared via hot-dipped aluminizing and subsequently high-temperature diffusion treatment. The phase, morphology and composition of aluminized coating were characterized by XRD, SEM and EDS methods. Comparative study was performed on unlubricated sliding wear behavior of plating under different substrates on a pin-on-disc wear tester, and the wear mechanism was explored. The results show that the coating is composed of ductile phases FeAl and Fe3Al. Kikendall porosity parallel to the surface exists around the interface of the two phases; because of the carbide particles agglomeration, the bond between the coating and H13 steel is apparently inferior to that in the case of 45 steel; the aluminized 45 steel possesses an excellent wear resistance under 50-200N at 400℃, whereas mild-to-severe wear transition occurs when the temperature increases to 600℃. The wear rate of the aluminized H13 steel reaches the lowest at 400℃, then slightly increases at 600℃. The wear mechanisms of Fe-Al coating are mainly predominated by oxidative mild wear, whereas the extrusion wear prevails in the process for aluminized 45 steel at 600℃.
Orthogonal test was carried out with ball-on-disc friction and wear tester in dry, deionized water, and simulated rain water under three loads (5, 10, 15N), respectively. The behavior of two materials at different loads under different environment was compared, the friction and wear properties of the alloys under the simulated service situation was explored. The composition of the samples was examined by X-ray diffraction (XRD). The contour of wear scars was detected by a three-dimensional surface profiler based on scanning white light interferometry. Optical electron microscope is used to observe the structure. The morphology of the worn surfaces were observed by scanning electron microscopy (SEM) and the wear mechanism was analyzed. Results show that due to the increase of Al, the body-centered cubic phase (bcc) substitutes the face-centered cubic (fcc) which attributed to the high hardness of Al1.3CrCuFeNi2 leading to good wear property. In dry condition, the wear mechanism are oxidation, adhesion, plastic deformation, and mild abrasive wear while in liquid, the abrasive is dominated along with oxidation and slight adhesive behavior.
The stress corrosion cracking (SCC) behavior and mechanism of M152 and 17-4PH high-strength steels in high Cl- environment were studied through neutral salt spray test and slow strain rate tensile (SSRT) test. The result shows that M152 and 17-4PH steels exhibit a certain sensitivity to SCC in Cl- environment, elongations of them both decrease with the increasing time of early neutral salt spray test, and the SCC sensitivity gradually increases. Comparing the fracture morphology with lateral crack through SEM, it can be found that the fracture mechanism of M152 and 17-4PH high-strength steels converts ductile fracture to brittle fracture as the extension of neutral salt spray test time. The synergistic effect of anodic dissolution (AD) and hydrogen embrittlement (HE) result in the occurrence of SCC in high Cl- environment, and Cl- can promote the AD process. Due to the obvious effect of HE, 17-4PH steel has higher SCC sensitivity than M152 steel with the same time of early neutral salt spray test. 17-4PH high-strength steel is more prone to SCC than M152 in high Cl- environment.
The 1Cr5Mo heat-resistant steel welded joint was annealed with CO2 laser, the effect of temperature on hot-stretching properties of the samples before and after laser annealing was analyzed by using stretching tests. The grain changes, rupture modes and fracture morphologies before and after laser annealing were observed by SEM, and the status of residual stress on the surface of welded joints was measured by using X-ray stress analyzer. The results show that the yield strength, tensile strength and elongation rate of the samples after laser annealing at 200℃ increase by 32.5%, 22.5% and 4.6% than those of the original samples, respectively, while after laser annealing at 300℃, they only increase by 6.6%, 6.5% and 7.5%, respectively; the tensile fracture of the samples before and after laser annealing is tough fracture, but the dimple size of the samples after laser annealing is bigger than that of the original samples, with the increase of temperature, the dimple size increases further; the grain refinement and residual compressive stress generated on the surface of the samples after laser annealing are the main factors of hot-stretching properties improvement.
The influence of loading direction and weld reinforcement on fatigue performance of TC2 titanium alloy TIG weld seam was investigated via fatigue experiments and SEM fracture observation. The results show that the fatigue life of retaining weld reinforcement specimens is lower than that of removing one in the same weld direction. The fatigue life of oblique weld specimens is higher than that of straight one with the same weld reinforcement treatment. The initiation of removing weld reinforcement specimens' fatigue crack sources is in the hole defect, but the weld reinforcement specimen initiate at the weld toes. During the early stage of fatigue crack propagation, the cracks all grow inside the weld seam metal with obvious fatigue striation. And the fatigue cracks of oblique weld specimens pass through the weld seam into the base with a typical toughness fatigue striation during the last stage of fatigue crack propagation. The dimple of straight weld specimens is little and shallow in the final fracture zone. The oblique weld specimens broke in the base metal area, and the dimple is dense.
Room Temperature vibration fatigue S-N curves of single crystal superalloy DD6 with[001] orientation was investigated and room temperature vibration fatigue limit was obtained. The fracture mechanism was studied by OM, SEM and EBSD. The results show that based on S-N method, vibration fatigue limit of DD6 single crystal superalloy with [001] orientation is estimated to be around 337.5MPa. Vibration fatigue fracture presents single or several {111} octahedral slip planes. SEM observations show that fracture has two regions:fatigue source region and the fatigue crack propagation regions, the fatigue cracks initiate at the surface or internal defect of the cross-section with the maximum stress, and exhibits a single source feature, fatigue crack propagation region exhibits quasi-cleavage fracture, no typical fatigue striation feature. Crystal plane slip along {111} is the main deformation mechanism of RT vibration fatigue fracture of single crystal superalloy DD6, quasi-cleavage propagation plane in fracture and quasi-cleavage patterns in microstructure are the main features of RT vibration fatigue fracture of single crystal superalloy DD6.
The influence of different shapes of centre notches on the tensile mechanical behavior of composite laminates was investigated by tension tests of composite laminates with circular notch and oblong notch. The strain concentration and failure process of notched specimens around the notch were analyzed intuitively with the strain distribution rule obtained during the tension test. A progressive damage model based on continuous stiffness degradation criterion was also developed to investigate the damage propagation processes of notched composite laminates. The results indicate that the proposed progressive damage model can accurately describe the tensile failure of notched specimens; and the strain concentration factor induced by oblong notch is more remarkable compared to that induced by circular notch, but the strain gradient around the oblong notch is larger; while the damage processes of the two types of notched specimens are quite different, the tensile strengths of both notched specimens are close.
A novel technology called pulsated orifice ejection method(POEM) and used for preparing mono-sized and high-precision spherical micro particles was introduced in this article. The working principle of the technique was illustrated and it was in two modes:low-melting point diaphragm mode and high-melting point rod mode, depending on the different melting points of materials. The particles prepared by POEM have the advantages of mono-sized, uniform and controllable particle size, high sphericity, and consistent thermal history. By introducing the application of particles prepared by this method, showing the huge application prospects of this technology in electronic packaging, bioengineering, micro-fabrication, rapid solidification analysis of metal droplets, additive manufacturing and so on.With the development of POEM, this technology is predicted to have wider prospects due to its unique characteristics.
|
Founded in 1956 (monthly) ISSN 1001-4381 CN 11-1800/TB Sponsored by AECC Beijing Institute of Aeronautical Materials |
