- 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)
The research status of graphene reinforced metal matrix aeronautical composites was reviewed, and its preparation methods were summarized. The effect of graphene on the properties of composites and mechanisms were discussed. At present, there is still lack of the research on the high content of aligned graphene reinforced metal matrix aeronautical composites. It was pointed out some related problems that need further study, including technological parameters, microstructure, interface chemistry and high temperature physical properties, etc. The emphasis of the future research should be changed from the process of preparation method to the design of micro composite configuration.
Graphene reinforced copper composites were fabricated by a one-step chemical reduction and spark plasma sintering. The effect of graphene content on microstructure, mechanical properties and electrical conductivity properties of composites was investigated by XRD, SEM, Raman spectrometer, tensile testing machine, nanoindentation, eddy current conductivity meter, etc. The results show that graphene is uniformly distributed within copper matrix and can evidently improve the mechanical properties of copper matrix. Compared to pure copper, the yield strength, tensile strength and elastic modulus of composites is enhanced by 219.8%, 35.9% and 6.9% separately with addition of only 0.025% (mass fraction) graphene oxide. Besides, the electrical conductivity of composites remains 93.1%IACS. With the increase of graphene content, the yield strength, tensile strength and elastic modulus of composites decrease. The main reason is that graphene is not well wrapped by copper particles with the increase of graphene content and the bonding between the naked graphene and copper matrix is poor, which weakens the strengthening effect of load transfer.
A new type globular MnO2 flowers anchored graphene composites was synthesized via redox reactions among potassium permanganate/ethanol/graphene. The crystalline structure, chemical component, and microstructure of the composites were determined by XRD, TG, SEM/TEM and BET analysis. The electrochemical test demonstrates the globular MnO2 material possesses excellent specific capacitance while poor rate capability and cycling stability. By means of anchoring these globular MnO2 flowers onto graphene, the specific capacitance of graphene is significantly improved. Meanwhile, rate capability and cycling stability of the globular MnO2 material can be promoted remarkably. In 0.5mol/L K2SO4 electrolyte, the specific capacitance of the composites reaches as high as 295F·g-1 at 2mV·s-1, and maintains at 102F·g-1 even at a high scan rate of 1000mV·s-1.An outstanding capacitance retention of 96.3% is achieved for the composites after 1000 cycles at 100mV·s-1. It demonstrates the globular MnO2 flowers anchored graphene composites is a very potential electrode material for supercapacitors.
Graphene nanoplates(GNPs), as toughening phase, toughened alumina-based nanocomposites ceramic cutting tool materials were fabricated by hot-pressing technology. The dispersing experiment of the GNPs was performed. The effects of different GNPs contents on the fracture toughness, flexural strength and hardness of the as-sintered ceramic cutting tool materials were investigated. The microstructure and morphology of GNPs were also observed. The results show that polyvinyl pyrrolidone(PVP) is the optimized dispersant of GNPs. When PVP addition is the 60%(mass fraction) of GNPs, the GNPs dispersion effect is the best. When GNPs addition is 0.75%(volume fraction), the fracture toughness and flexural strength of the cutting tool material reach up to 7.1MPa·m1/2 and 663MPa, which increase by 31% and 15% compared with that without GNPs addition cutting tool material. The crimped GNPs disperse well in the matrix material. The main toughening mechanisms include GNPs rupture, GNPs pull-out and cracks defection. Comparing with no GNPs addition cutting tool material, GNPs toughened cutting tool material shows lower main cutting force, cutting temperature and rake friction coefficient, and better wear resistance.
Cellulose nanocrystal (CNC) plays a more and more important role in the process of designing and assembly of functional materials, due to its high strength and modulus, controllable structure, feasible modification, biocompatibility and biodegradability. As a kind of macromolecule system with "intelligent" behavior, the stimuli-responsively functional materials make a sensitive response when stimulated by the external environment, and show the corresponding function. With the addition of CNCs, not only the mechanical properties of CNC-based functional materials are greatly improved, but also the hydroxyl and carboxyl groups on the surface of CNCs provide a convenient way to enrich the stimulus response source of these functional materials. Herein, combining with the chemical structure of CNC, the synthesis of CNC-based stimuli-responsive functional materials was comprehensively summarized. Meanwhile, the recent developments of single or multiple stimuli-responsive functional materials based on CNCs, such as water-, thermal-, pH-, light-responsive functional materials were summarized, with the stimulate switch taken as the main line. Finally, it was pointed out that future research would focus on improving the surface-modification efficiency of CNC, and broadening multi-stimulus responsiveness of CNC-based functional materials. The preparation of CNC-based functional materials with high performances will be significant in the future research as well.
With the increase in environmental awareness, reducing the use of petroleum-based materials has become a social consensus, so the researchers have been greatly interested in the bio-based furan derivatives which have a great potential for the applications in bio-based coatings, self-healing coatings and photocurable coatings because of their unique properties. However, there is no mature study in our country. Based on this, the application in bio-based coatings, self-repair coatings and other coatings was summarized in this paper, and then the recent research achievements of furan derivatives in organic coatings at home and abroad were introduced and analyzed, and the difficulties in the large-scale application of furan derivatives were pointed out as follows:the high production cost. Finally, other applications of furan derivatives were analysed and prospected, for example, utilizing furan methyl glycidyl ether as reactive diluent of epoxy coatings to replace commercial petroleum-based reactive diluent and non-covalent modifying graphene using the delocalized π bond of furan ring for preparing graphene/organic coatings composites.
The porous Co3O4 hollow nanospheres were synthesized via hard template method by a carbon spheres templated strategy. The morphology and structure of materials were studied by SEM, XRD, FTIR, BET and XPS. The structure and gas sensing properties of Co3O4 hollow nanospheres were controlled by changing the concentration of precursor and aging time. The results show that the Co3O4 hollow nanospheres with diameter of 500nm composed by 40nm Co3O4 nanoparticles can be synthesized with 0.1mol/L precursor and aging for 48h. The surface of nanospheres is porous structure. The synthesized Co3O4 hollow nanospheres sensor have good gas response to 100×10-6-0.5×10-6 NH3 at room temperature. The gas sensitivity to 100×10-6 NH3 reaches 155.8% and the response time is 1.3s. The limit level of this gas sensor to NH3 is 0.5×10-6.
Superhydrophobic surfaces with excellent hydrophobic properties were prepared by chemical redox process. The surface wettability and morphology were characterized and analyzed by contact angle measurement and scanning electron microscopy(SEM). The contact angle of the superhydrophobic surface is as high as 163.31°, and the sliding angle is less than 5°. The effect of different reaction time on surface morphology and wettability was investigated, the performance of the static water droplets and the dynamic anti-icing performance of the superhydrophobic surface was explored by using a self-made icing testing system, and the experimental results were analyzed by combining the one dimensional heat transfer theory and classical nucleation theory. The results show that the surface hydrophobicity is the best when the reaction is 80min. The delay icing time of static water droplets on superhydrophobic surface is about 5 times than the normal sample, icing temperature is also low 3.3℃. There is no accumulated water and ice from start to end on superhydrophobic surface when water droplets impacting the cold surface. The as-prepared superhydrophobic surfaces show excellent static and dynamic anti-icing performance.
The Ni0.5Zn0.5Fe2O4 nano absorbing materials were prepared by two-step method(coprecipitation method combined with sol-gel method), and the microwave absorption influence of the calcination temperature of the precursor in sol-gel method were explored. Moreover, the microstructure and electromagnetic properties of the as-prepared samples were characterized by the X-ray diffraction (XRD), atomic force microscope (AFM), vector network analysis (VNA). Consequently, XRD analysis indicates that the pure Ni0.5Zn0.5Fe2O4 nanoparticles can be obtained while the temperature is higher than 650℃. The AFM results show that the microstructure size of the samples tends to be smaller and more uniform while the temperature is increased. Besides, the VNA results indicate the Ni0.5Zn0.5Fe2O4 exhibits best electromagnetic properties within 2-12.4GHz at the calcination the temperature is 650℃, and the as-prepared samples possess excellent microwave absorption performance. The qualified absorption bandwidth reaches 4.9GHz, and the maximum reflection loss reaches -24.94dB.
A barium ferrite microwave absorbing coating based on metamaterial structure was designed. The influence of metamaterial structure on the absorbing properties of this coating was analyzed, and the absorbing mechanism of coating was studied and discussed. Through simulation, it is found that the absorbing properties of barium ferrite have been greatly enhanced with metamaterial structure. The optimum value of the coating thickness(2.5mm) and sheet resistance(70Ω/□) are unique, meanwhile, the widest absorbing bandwidth of the coating is achieved. There exist two absorption peaks and the reflection loss can reach -10dB within the frequency range of 8-18GHz. The results show that the absorbing properties of barium ferrite are improved immensely with metamaterial structure design.
In order to ensure the full melting of the thermoplastic composites (TPC) prepreg in the process of automated fiber placement (AFP) and offer the potential to realize the in-situ consolidation for TPC, it is necessary to control the temperature of the prepreg in AFP. Aiming at the processing speed will be changed within the larger scope, an infrared heating technology with fast response rate and efficient was proposed. Based on the analysis of the heat transfer process between the infrared heat source and the layers, the control equation of dynamic temperature was put forward and the matching relationship between the radiation intensity and laying speed was established. Based on the AFP platform, the infrared heating system which adopts the feedforward control method was constructed and the corresponding control strategy was formulated according to the dynamic thermostatic control equation to realize the heating temperature of prepreg controlled accurately. The experiment results show that the infrared heating thermostatic control system can meet the requirement of dynamic thermostatic control in the condition of variable speed and the compressive strength and the interlaminar shear strength for AFP component are closed to the moulded component.
To improve flame retardant properties of polypropylene, the brominated epoxy resin (BEO) and nano-Sb2O3 were added into polypropylene by using a high energy ball milling technique. Flame retardant properties of polypropylene composites were evaluated by UL94 vertical combustion tests and limit oxygen index (LOI). The surface morphology of combustion products of composites was characterized by scanning electron microscopy(SEM) and the flame-retardant mechanism of flame retardant additives acting on the polymer matrix was studied by using thermo gravimetric analysis(TGA) and Fourier transform infrared (FT-IR) spectroscopy. The results show that the reaction between modified nano-Sb2O3 and BEO can prolong residence of the halogens in the combustion area, resulting in more hydroxyl and hydrogen radicals are replaced by the bromine radicals. When the content of modified nano-Sb2O3 is 7% (mass fraction, the same below) and that of BEO is 21%, the nano-Sb2O3/BEO/PP composite has excellent flame retardant performance with 28.6% of LOI value and V-0 of UL94 grade of vertical combustion.
Hexa (imidazolyl) cyclotriphosphazene (HImCP) was synthesized by nucleophilic substitution reaction of hexachlorocyclotriphosphazene with imidazole. The chemical structure was characterized by FT-IR, 1H-NMR, and 31P-NMR. Then the as-prepared HImCP was utilized as curing catalyst for curing of diglycidylether of bisphenol A(E51)with methylhexahydrophthalic anhydride(MHHPA). Its influence on the storage stability at room temperature and curing activity at high temperature of E51/MHHPA system was studied by gelatum time and non-isothermal DSC analysis. The mechanical performance, glass-transition temperature(Tg), and thermostability of the obtained epoxy thermosets were also investigated. The results show that HImCP is a good latent curing catalyst contrast with unmodified imidazole. When the epoxy resin curing system contains 1% (mass fraction) of HImCP, it exhibits improved storage stability at room temperature as compared to that containing imidazole, as well as satisfied curing activity at high temperature. In addition, the obtained thermoset has higher tensile strength, Tg and thermostability than that resulted from imidazole.
By means of the electrochemical workstation, scanning electron microscope, energy spectrometer and so on, the polarization curves and galvanic corrosion parameters of the front surface (FS) specimen and side surface (SS) specimen of CF8611/AC531 composite and the 7B04-T74 aluminum alloy in the electrolyte of 3.5% (mass fraction, the same below) NaCl or 3.5%NaCl+12.5% Cu2SO4 were measured, meanwhile the microstructure were observed. Based on the electrochemistry theory, steady corrosion field and parametric scanning technology, a dynamic model for galvanic corrosion under the wear status of composite was established. The results show that the performance of this composite is stable, but there are some carbon fibre exposed defects on the original surface. The defects are often located at the overlap area of carbon fibre bundles. There are 4.3 defects per square millimetre and the average area of each defect is 0.0184mm2; the cathodic reaction rate is closely related to the area of the defects and consequently its surface is divided into the active and the inert cathode region; in the galvanic corrosion the main corrosion form of the aluminum alloy is pitting and no failure is found in the composite. The galvanic corrosion model established here is valid and available. There is a positive linear correlation between the total galvanic current Ig and the defect area S; the galvanic effect of FS and SS on the aluminum alloy is the same when SFS:SSS is about 5.53:1.
The Al0.1CoCrFeNi high-entropy alloy (HEA) was melted by vacuum magnetic levitation, and quasi-static tensile experiments were performed by using an INSTRON mechanical testing system. The crystal structure, surface morphology, composition, microstructure, hardness, and creep behavior of the samples before and after the experiment were analyzed by X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, and nanoidentation. Results reveal that after tensile deformation, the alloy has an excellent strength-ductility combination, a significant strain-hardening effect, and an improved creep resistance. The fracture mode of sample is the typical microvoid accumulation fracture; there are a lot of microbands (the band width is about 200-300nm) inside the grains. The excellent strain-hardening ability is believed to be originated from the microband-induced plasticity effect during tensile loading.
The Mo-Cu nano-powders were synthesized by a microwave-assisted aqueous solution strategy and subsequent low-temperature hydrogen reduction process. The sintering densification behavior of Mo-Cu composite powders and the sintering properties of the composite compacts were investigated. Results show that the sintering temperature is a critical factor in the densification process of Mo-Cu composites. The shrinkage rate, density and hardness of sintered composites increase as the temperature rises. However, too high sintering temperature causes significant loss of copper phase and abnormal grain growth, resulting in decrease in density, hardness, electrical conductivity and thermal conductivity. By optimizing all the performance indicators, high performance Mo-25%Cu composites with homogeneous microstructure accompanied with good physical and mechanical properties can be obtained by sintering for 2h at 1100℃, for the actual chemical composition is highly close to the designed chemical composition. The density, hardness, bending strength, electrical conductivity and thermal conductivity are 9.79g/cm3, 229.1HV, 837.76MPa, 24.97×106S·m-1 and 176.57W·m-1·K-1, respectively.
The stabilities of microstructures and hardness of P92 steel samples austenitized at 1060℃ for 1h followed by air cooling (AC)/slow cooling (SC) and tempered at 760℃ for 2h and then aged at 650℃ for 1000h/3000h were studied by SEM-SE/BSE, EDS and multiphase separation technology (MPST). The results show that the microstructures of P92 steel aged samples consist of martensite and precipitations (M23C6 and Laves phase). The cooling modes after austenitization have an obvious effect on microstructures and hardness of the samples aged at 650℃. Compared with the AC samples, the total volume fraction of the precipitations/Vickers hardness of the SC sample is higher/lower and the volume fraction of the Laves/M23C6 phase is remarkably higher/lower. Moreover, the Laves phase particles of SC sample is much more coarsened. The hardness of the SC sample decreases after ageing treatment at 650℃ for 1000h/3000h, while that of the AC sample is not obviously varied. In addition, the stabilities of microstructure and hardness of P92 steel aged at 650℃ are related to the stability of the austenite which in return affects the stability of the martensite transformed during cooling. Therefore, the P92 pipes cooled from austenitization should dissipate heat as soon as possible in the manufacturing scene.
Microstructure and fracture morphologies of as-deposited TC4 samples fabricated by rapid manufacture of electron beam selective melting (EBSM) were observed and analyzed by a digital microscope and a scanning electron microscope respectively. The influence of different build geometries and load directions on the fracture properties was studied. The results indicate that fracture properties of vertical samples are influenced by columnar crystals and characterized by its anisotropy. The fracture toughness (KIC) in the deposition direction of vertical samples is 94.94MPa·m1/2, which is greater than that in the electron beam scanning direction (85.33MPa·m1/2), and the elongation (δ) of 3% is very low; α morphology has some influence on the fracture properties. The elongation (δ) and fracture toughness (KIC) in horizontal samples with lamellar α colony are greater than that in vertical samples with crossed acicular α, and the maximum is 14.5% and 101.45MPa·m1/2, while the ultimate tensile strength (σb) and the yield strength (σ0.2) are lower; furthermore, the fracture of EBSM-TC4 samples consists of different sizes of dimples and circuitous tearing ridges. So the fracture method is characterized by ductile dimple-based intergranular fracture and the circuitous degree of tearing ridges as well as size and depth of dimples on the fracture morphologies of horizontal samples are greater than that in vertical samples.
The distribution of in-plane shear modulus and strength of 2D-C/SiC composites, and its B-basis value of strength were studied by testing thirty Iosipescu specimens under shear load. The distribution and parameters about in-plane shear properties of 2D-C/SiC composites were determined by the method that liner regression combined with hypothesis testing, and the statistics results obtained by two different empirical failure probabilities were compared. The mechanism of the dispersibility of the in-plane shear strength was demonstrated by the micro-CT(μ-CT)photographs and SEM(scanning electron microscope) photographs through observation on the narrowest net cross-section. Finally, the Weibull B-basis value of the strength was calculated based on the distribution law. The results show that the strength and modulus of 2D-C/SiC composites both follow weibull, normal and lognormal distribution, and the prediction has good agreement with test data. The distribution of the mechanical properties is not affected by two empirical failure probabilities. The dispersibility of the strength is connected with the density of the narrowest net cross-section and the interface debonding length. Finally, its B-basis value of strength is 80.41MPa.
Considering the residual stress, residual strain and residual strain energy, the influence of shot peening on the J-integral parameters of semi-elliptic surface crack front was quantitatively calculated and analyzed. The shot peening process was simulated, the fatigue crack was generated by changing the constraint condition and far field load was applied to calculate the J-integral and crack propagation rate. The effect of semi-elliptic surface cracks with different depth and different shot velocities on fracture parameters was analyzed. The results show that when shot velocity is a certain value, the reduction of the J-integral value after shot peening decreases with the increase of the crack depth compared with that without shot peening, which indicates that shot peening is more beneficial to suppress the fatigue crack propagation. When the crack depth is 0.3mm, the J-integral value of the deepest point of the crack front reduces from 4.25N/mm to 2.99N/mm, and the reduction is about 30.1%.The J-integral value decreases with the increase of shot velocity when crack depth is a certain value, therefore, increasing shot velocity is more beneficial to retard the fatigue crack propagation.
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