- 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)
Based on the design concept of aircraft landing gear, the recent achievements in research and development on both ultra-high strength steels and ultra-high strength stainless steels (UHSSS) for the landing gear in aircraft were reviewed. The composition, microstructure and mechanical properties of typical commercial UHSSS grades that were produced and used were also summarized. It was then proposed that the future research on UHSSS with the improved combination of strength and toughness should focus on designing both composition and processes of new UHSSS grades by using the up-to-date material thermodynamic and kinetic calculations, particular attention should be paid to microstructural designing on either high density coherent or multi-type nanosized precipitation and the deliberate tailoring of retained austenite with enhanced mechanical stability for toughening; both of them could contribute to the strengthening and toughening of UHSSS. Finally, the updated hot working technology was put forward, the isothermal multi-direction forging, which could significantly improve the comprehensive mechanical properties of UHSSS.
The current research progress in the influence of static magnetic field on the microstructures of directionally solidified Ni-based superalloy at home and abroad was reviewed, and the effect of different ways, strength of static magnetic fields on the dendritic microstructure, elemental segregation, solidification defects and high temperature mechanical properties was emphatically analyzed. The potential development of static magnetic field in directional solidification of nickel-based superalloy was proposed from the control of stray crystals at variable cross-sections, the control of crystal orientation deviation, and the influence mechanism of static magnetic field on solidification properties.
The graphene oxide was prepared via one step under low-temperature with natural flake graphite as raw material. Factors affecting oxidation degree and layer spacing of graphene oxide were discussed in the process of low-temperature oxidation, such as the dosage of oxidant and oxidation time in system. The results indicate that high C-O bond and low defect structure (ID:IG=0.63) graphene oxide with the carbon and oxygen atom ratio of 1.98 can be prepared in the condition of the potassium permanganate with natural flake graphite mass ratio of 1:3, oxidation temperature of 0℃, oxidation time of 48h.This way avoids the increase of graphene oxide defects in the process of Hummers preparation due to the formation of CO2, which leads to the hexagon fracture and the absence of carbon atoms. After microwave reduction, the reduced graphene oxide with low defect is obtained, which the distance between defects(LD)is 12nm, the defect density(nD) is 2.21×1011cm-2 and the ratio of ID:IG is only 0.85 (ΓG=32.1cm-1).
Carbon nanomaterials based sensing technology has become a promising technology in the field of structural health monitoring of composites. Self-sensing composites were achieved with varied sensing elements, including carbon nanotube (CNT) coated fibers (CNTF) and reduced graphene oxide (RGO) coated fibers (RGOF), to compare their sensing performance and mechanism. Piezoresistive response of varied sensors show that RGOF has higher piezoresistive sensitivity and clearly exhibits two-stage behavior from linear to non-linear; whereas, CNTF always exhibits a smooth and orderly electrical signal before fracture occurs. This strong structure-property relationship can be explained by resin infiltration theory. For CNTF, resin molecules can penetrate its porous network structure, forming a complete CNT/resin nanocomposite structure integrated on the fiber surface. In contrast, RGOs with large lateral dimensions and surface consistency can form non-invasive network structure that impedes resin penetration. Further analysis and study show that CNTF is more suitable for long-term monitoring and mechanical state recognition, while RGOF is more practical for the early warning of structural damage.
The 600℃ high temperature titanium alloy composite with graphene oxide addition was prepared by temperature-controlled mixing method and hot isostatic pressing. Microstructure and mechanical properties of composite were studied by metallographic observation, energy spectrum analysis, phase analysis and tensile test. The results show that graphene oxides are dispersed uniformly in the 600℃ high temperature titanium alloy powder when the content of graphene oxide is 0.3%(mass fraction) and the main mode of action is physical adsorption. Compared with the alloy without graphene oxide, the microstructure of the composite with 0.3% graphene oxide is obviously refined, and the average size of equiaxed alpha phase is reduced by 36%. Meanwhile, the average room temperature tensile strength and yield strength increase by 7.8% and 10.4% respectively and Vickers hardness increases by 25.6%. The strengthening mechanisms of graphene oxide on 600℃ high temperature titanium alloy mainly include grain refinement strengthening, dislocation streng-thening and precipitation strengthening of the (TiZr)6Si3 second-phase.
The cyclic torsion was carried out on the extruded AZ31 magnesium alloy rods at room temperature by using a computer controlled torsion testing machine. The texture of initial extruded magnesium alloy rods was measured by the XRD technique, which displays a typical basal texture. The mechanical properties during deformation were measured, and the microstructure and texture feature after torsion were analyzed by the EBSD. Meanwhile, the effect of cyclic torsion on mechanical properties of magnesium alloy rods was also investigated. The results show that the symmetrical stress-strain hysteresis curves are obtained during the cyclic torsion of magnesium alloy rods, revealing that sliding is the dominant deformation mode during former torsions, moreover, the stress peak values of the hysteresis curves present an increasing first and then decreasing trend with the increase of cycle period, which is dominated by work hardening and internal micro-crack propagation. The stress peak forms at the 4th cycle under conditions of 60ånd 90°maximum torsion angles, respectively. Amounts of extension twinning bands formed within grains after torsion of magnesium alloy rods, c-axis of grains is rotated to the axial direction of bars caused by the activation of twinning. Mechanical properties of twisted magnesium alloy rods tested by computer controlled universal testing machine show that the compression yielding strength of magnesium alloy bars is increased by the cyclic torsion, the value of which is increased from about 100MPa before torsion to about 200MPa after torsion at most.
The hot deformation behavior of Cr-Mo-B mechanical engineering steel was conducted at deformation temperature of 850-1150℃ and strain rates of 0.1-10s-1. The artificial neural network(ANN) model was developed based on the true stress-strain curves, where the input parameters were deformation temperature, strain rate, strain, and flow stress was the output parameter. The results show that the ANN model is accurate in predicting the flow stress, and the root mean square error is 1.3858. Based on the dynamic material model (DMM), the processing maps of the studied alloy at true strains of 0.5 and 0.7 are constructed to recognize optimum hot deformation regions:the optimum region for the strain of 0.5 is at deformation temperature of 1050-1150℃ and strain rate of 0.1-0.4s-1 with a peak power dissipation factor of about 37.20%, and the optimum region for the strain of 0.7 is at deformation temperature of 1000-1150℃ and strain rate of 0.1-0.6s-1 with a peak power dissipation factor of about 35.80%.
In order to improve the high-temperature (HT) microstructural stability of 310S-type austenitic stainless steels (ASSs), the effects of minor-alloying elements (Nb, Ti, Zr, and W) on the precipitation behaviors and mechanical properties of 310S ASSs were systematically investigated. The designed alloy ingots were hot-rolled at 1423K, solid-solutioned at 1423K for 0.5h, stabilized at 1173K for 0.5h, and then aged at 973K for different hours. The microstructure and precipitated phases at different heat-treatment states were characterized by XRD, OM, SEM-EDS and TEM, respectively. It is found that the addition of Ti or Zr can refine the matrix grains remarkably, but Ti can deteriorate the HT microstructure stability of alloy sharply, i.e., a large amount of coarse Cr23C6 and σ particles are precipitated both on GBs and in the matrix after long-term aging. In addition, the impurity of Si should be controlled strictly for the inhibition of G-Ni16Si7Zr6 phase precipitation in Zr-containing ASSs. Mo accelerates the phase transformation of Cr23C6 to (during aging, while W plays an active contribution to the HT microstructure stability. The designed Fe-25Cr-22Ni-0.73Mo-0.35Nb-0.046C (mass fraction/%) alloy exhibits excellent mechanical properties (σYS=237MPa, σUTS=545MPa, δ=39%) due to its higher microstructural stability at 973K, which is expected to be applied as fuel claddings.
The binding energies, electronic structures and mechanical properties of M doped in α-Fe(N) system were investigated by using first principle calculations, where M represents Ti, V, Cr, Mn, Co, and Ni. The results show that Ti and V occupy preferentially the corner of α-Fe(N) unit cell, Cr and Mn occupy preferentially the body-centered position of the cell, the structure is the most stable when Co and Ni are not adjacent to the N atom. The doped elements Ti and V strengthen the stability of α-Fe(N); Cr, Mn and Ni have an opposite effect; Co does not affect the stability. The metallic and ionic bonds coexist in the doped systems. The bonding orbitals are created by the interaction of M3d, Fe4s3p3d and N2p. Compared with the pure α-Fe system, the material rigidity is stronger for doped systems. The calculation results show that the elastic modulus E, shear modulus G and bulk modulus B of α-Fe(N)-V are the maximum. It reveals that doped V can significantly improve the overall mechanical properties of steel and it is the most effective nitrogen fixing element. It is consistent with the experimental results of high nitrogen steel smelting.
In order to further explore the mechanism during electron beam welding, electron beam welding was carried out on a 10mm 2219 aluminum alloy. A three-dimensional electron beam welding model in which volume of fluid (VOF) was combined with dynamic heat source was established using numerical software Fluent to simulate the coupling between keyhole and molten pool. The process and formation of vortex in molten pool were analyzed, the interaction between electron beam and keyhole was also identified and discussed. The results show that the molten pool is divided into three parts through the analysis of liquid metals. The liquid metal in zone Ⅰ maintains the stability of the volume of the molten pool. The surface of the molten pool is enlarged by vortex in zone Ⅱ. Vortex in zone Ⅲ plays an important role in causing the keyhole to collapse. The coupling analysis of electron beam and keyhole wall shows that the electron beam is not uniformly distributed on the keyhole wall, which results in a certain hysteresis at the bottom of keyhole.
The friction stir additive manufacturing (FSAM) experiment was conducted with 2mm thick sheets of 2195-T8 Al-Li alloy by using five tools with various shapes. The influence of stir tool shape and additive process on the formation, the interface defects and the hardness distribution of friction stir additive manufactured build was mainly investigated by metallographic observation and hardness testing. The results show that there is no obvious mixing of the materials across the interface of the builds manufactured by the cylindrical pin and the conical pin with three flats. However, the TrivexTM pin and the pin with three concave arc grooves are good for mixing of the materials across the interface and reducing hooking defects. Dense and defect free metallurgical connection occurs at the interface on the advancing side of the nugget zone. However, the materials across the interface on the retreating side are not sufficiently mixed, hence the hooking defect on the retreating side is easy to extend into the nugget zone, and the weak-bonding defect is originated from the hooking defect on the retreating side. For the four-layer build, except for the top layer, the welding method that the welding directions of two adjacent layers are opposite can make the hooking defects on both sides of the other layers bend to the outside of the nugget zone and improve the weak-bonding defects. The hooking defect on the retreating side of the top layer extends into the nugget zone. There is an obvious softening phenomenon in the nugget zone of the builds. The distributions of the hardness of the nugget zones of the builds manufactured by different welding processes are uniform, which shows that the build with uniform properties can be obtained by friction stir additive manufacturing. Compared with the single pass welding method, the back and forth double passes welding method further softens the material of the nugget zone of the one-layer build. For the four-layer build, the closer the layer is to the top, the higher the average hardness of the nugget zone is.
The porous TiO2 powders were prepared by sol-gel method using titanium tetrachloride as titanium source, P123 as template agent and cyanamide as stabilizer agent, respectively. The porous TiN powders were synthesized via reduction and nitridation of the porous TiO2 powders at 900℃ in NH3. The phase composition and microstructure of the porous TiN powders were characterized by the XRD, SEM, BET, TEM and SAXD. The electrochemistry performance of the porous TiN powders was evaluated through the cyclic voltammetry, AC impedance and constant current charge-discharge techniques. The results show that the porous powders have approximate spherical particles with cubic TiN phase. Compared to the porous TiN powders without P123 adding, the mesopores with pore diameter range of 10-50nm increased in the porous TiN powders with P123 adding. There are also some pores with size range of 2-3nm. Meanwhile the porous TiN powders with P123 adding exhibit more ordered mesopores. This porous structure can improve the electrochemistry performance of the TiN powders. As a result, for the porous TiN powders without P123 adding, the specific capacitance is 81F·g-1. The internal resistance R1 is 1.1Ω, and the ion diffusion impedance W1 is 2.5Ω. For the porous TiN powders with P123 adding, the specific capacitance is increased to 95F·g-1, the R1 and W1 value are decreased to 0.9Ω and 0.06Ω, respectively.
The β-Li3PS4 solid electrolyte with high ionic conductivity and low activation energy was prepared by wet chemical method and stepwise heated to remove tetrahydrofuran molecules from the precipitate. The morphology, structure and phase composition of the products at different treatment stages were studied by means of simultaneous thermal analysis, X-ray diffraction, scanning electron microscopy, Raman spectroscopy, N2 adsorption/desorption and AC impedance spectroscopy, and the electrochemical performance of β-Li3PS4 solid electrolyte were analyzed. The results show that the specific surface area of the nanoporous β-Li3PS4 solid electrolyte prepared by this method is 28.3m2·g-1 and its average pore diameter is about 23nm. Electrochemical characterization shows that the ionic conductivity of the electrolyte at 20℃ is 1.84×10-4 S·cm-1, the activation energy is 0.343eV, and the electronic conductivity is 1.3×10-8S·cm-1. In addition, the electrolyte has excellent electrochemical stability and good compatibility with the lithium anode.
Li2MnSiO4 cathode material for lithium ion batteries was successfully synthesized using a high pressure hydrothermal method.The influences of pressure, reaction temperature and precursor concentration on the preparation of Li2MnSiO4 were carefully studied. The structure, morphology and electrochemical properties of the samples were characterized and analyzed using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electrochemical test. The results show that well crystallized Li2MnSiO4 with high-purity material can be synthesized at high pressure. Moreover, higher precursor concentration is conducive to the formation of nanoscale particles of Li2MnSiO4. Electrochemical performance tests show that carbon-coated Li2MnSiO4/C composite has higher specific capacity than that of Li2MnSiO4.An initial specific discharge capacity of 178.6mAh·g-1 can be achieved for the Li2MnSiO4/C cathode material at 0.1C (the current density is 33.3mA·g-1) and a capacity retention of 97.1mAh·g-1 after 50 cycles is 54.4%. At the same time, Li2MnSiO4/C also shows smaller charge transfer resistance and higher lithium ion diffusion coefficient than that of Li2MnSiO4.
In order to improve the safety and reduce interface impedance of lithium-ion batteries, the star-shaped polyhedral POSS-poly(methyl methacrylate) (POSS-(PMMA46)8), which has both excellent heat resistance and good compatibility with the polymer material, was selected as a modifier to modify the separator of commercial polypropylene (PP) by the method of impregnation. The micromorphology of the composite separator was studied by scanning electron microscope (SEM). The mechanical property of the separator was measured by a tensile tester. The thermal stability of the separator was studied at a high temperature. The wettability of the separator was tested by a contact angle tester. The AC impedance was used to obtain the bulk impedance of the composite separator and then its ionic conductivity was studied. The electrochemical stability of the separator was measured by linear sweep voltammetry (LSV). The results show that when the mass fraction of POSS-(PMMA46)8 is 40%, the pore distribution of the composite membrane is homogeneous, and the wettability is the best. The tensile strength is 5.34 times that of the original film, and the thermo-stability is ideal at 160℃/1h. The conductivity of the composite membrane is 1.35×10-3 S/cm. The interface resistance between the composite separator and the electrode is reduced from 743Ω to 152Ω, and which is 79.5% higher than that of the original film; for Li/Separator/LiFePO4 cell, the charge-discharge cycling stability is better and the battery capacity at low magnification is comparable to commercial PP separator.
Advances in multi-electron transfer materials and architectured electrodes are two important strategies for innovations in electrochemicalenergy storage. The attainment of both by interfacial electrodeposition of freestanding PPy-PEDOT copolymer films was reported. The composition of the copolymer was verified by FTIR and XPS spectra.The dispersion and microstructure of PPy and PEDOT were studied by EDX mapping and SEM. The capacitive performances of the copolymer films were studied by electrochemical measurements. The results show the copolymer film is composed of PPy and PEDOT with homogeneous distribution in a certain proportion.The SEM images show the film exhibits heterogeneous microstructure and has an open porous 3D network microstructure. Electrochemical characterization shows that the copolymer film is an excellent supercapacitor electrode material with high specific capacitance, good power capability and cycle performance. The multi-electron transfer nature of the copolymer, the copolymerization synergistic effects and the unique microstructure are responsible for the improved charge-discharge performances.
The periodic structure coating maintenance process based on the selective surface was proposed. The coating of oxidized Fe and carbonyl iron particles (CIPs) was obtained by the corrosion method. The morphology of particles after corrosion was characterized by the scanning electron microscopy (SEM). The permittivity and permeability of the absorber adding the hybrid particles were tested in 8-18GHz, and the oxidized coating parameter could be calculated using the effective medium rule. Effects of the corrosion process and the maintenance process were analysed. The results show that as the CIPs oxidized in the coating surface, the coating's absorbing property was weakened as the oxidization thickness is increased, and the increment value of reflection loss (RL) is about 2dB. When the coating thickness is set as 0.8mm, the maintenance performance is unsuitable. However, if the coating thickness is increased to 1mm and the oxidization thickness is 0.1mm, the maintenance performance is improved, then the absorbing band can be widened in 10-18GHz and the RL decrement is about 2dB correspondingly.
The TiO2/g-C3N4 composites were prepared by the hydrothermal method with cetyltrimethyl ammonium bromide (CTAB). The influence of CTAB on the structural properties and spectral properties of the composites was studied. The samples were characterized by XRD, TEM, N2 adsorption-desorption, FT-IR, UV-Vis DRS and PL, meanwhile, the samples were used to degrade unsymmetrical dimethyl hydrazine (UDMH) wastewater under visible light. The results show that the crystal structure of TiO2/g-C3N4 composites assisted by CTAB is intact, with smaller particle size of nanoparticles and uniformly distributed on g-C3N4 sheets. The specific surface area of the composites increases and the mesoporous is more abundant, the adsorption ledge of the composites is expanded to 450nm, the recombination rate of hole-electron reduces obviously. Photocatalytic results show that the UDMH degradation efficiency of TiO2/g-C3N4 (CTAB) reaches 83.2% in 120min, which is improved by 13.7% than that of the no CTAB-assisted composites.
Tourmaline/ZnO composite material was prepared by one-step hydrothermal method. The structure, morphology and optical properties of the samples were characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence spectroscopy and UV-Vis DRS. Under visible light irradiation, the photocatalytic performance of tourmaline/ZnO composite was studied using acid fuchsin as a degradation product. The kinetic model was used to simulate the degradation process of acid fuchsin. The results show that the addition of tourmaline does not affect the morphology of ZnO petals, but has a great influence on its photocatalytic properties. With the increase of the content of tourmaline, the photocatalytic performance first increases and then decreases. When the content of tourmaline is 5%(mass fraction), the recombination probability of photogenerated electron-hole decreases, the forbidden band width decreases, the concentration of hydroxyl radical (·OH) increases and the photocatalytic efficiency reaches the maximum 96.62%, ZnO and tourmaline/ZnO catalytic degra-dation of composites follows a first-order kinetic model.
Mode Ⅱ interlaminar fracture toughness is an indispensable mechanical performance parameter for damage tolerance design of composite structure. The domestic T300 composite end notched flexure (ENF) specimens with five different delamination interfaces were tested for mode Ⅱ delamination form, mode Ⅱ interlaminar fracture toughness GⅡc, NPC corresponding to the delamination initiated at the film insert and the mode Ⅱ interlaminar fracture toughness GⅡc, PC of the delamination growing from the pre-cracking were obtained. For five delamination interfaces, the values of GⅡc, NPC are higher than that of GⅡc, PC. For GⅡc, NPC values, GⅡc, NPC of the 0°/0° interface is the highest, GⅡc, NPC of the 0°/90° interface are the lowest. For GⅡc, PC values, GⅡc, PC of the 0°/45° interface is the highest, GⅡc, PC of the 0°/90° interface is the lowest. In addition, VCCT was used to simulate the mode Ⅱ delamination process, from which the strain release energy distribution at the delamination front during propagation along different interfaces was obtained. The effect of the delamination interface on the mode Ⅱ fracture toughness was investigated combined with the experimental results.
In order to quantitatively characterize the ability of PVD(physical vapor deposition) film sensors to detect cracks in metallic structures, the process parameters applied to LY12-CZ aluminium alloys were first optimized using orthogonal tests, and coin shape, 1mm concentric dual ring shape, 0.5mm concentric tricyclic shape PVD film sensors were prepared on three groups of specimen with central hole using these parameters. Subsequently, the on-line monitoring experiment of fatigue cracks was carried out under laboratory conditions, the potential output signals of the PVD film sensors and microscope observations were compared and analysed. Finally, the probability of detection curves of all kinds of PVD thin-film sensors and PVD film sensor in different shapes were plotted separately using the improved crack size separation method and binomial distribution detection model. PVD thin-film sensors have 93.56% detection probability for cracks with length greater than 0.99mm at 95% confidence level. Compared to coin-shaped thin-film sensors, concentric ring shape film sensors are more sensitive to cracks smaller than 0.5mm, and the sensors with finer channel width have the higher probability of detection on small size cracks.
|
Founded in 1956 (monthly) ISSN 1001-4381 CN 11-1800/TB Sponsored by AECC Beijing Institute of Aeronautical Materials |
