- 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)
Buckypaper/polymer composites can take more advantages of the superior properties of carbon nanotubes (CNTs) and possess enhanced properties than traditional CNT/polymer composites, for the aggregation of CNTs is low and the CNT content is high. However, due to the dense structures of Buckypaper, the traditional infiltration technique cannot meet the requirements for fabricating high quality Buckypaper/polymer composites. A pressurized infiltration technique was developed to enhance the infiltration efficiency and quality. The epoxy solution was pressurized infiltrated through the Buckypaper, resulting in a well infused Buckypaper. The micro-structure characterization indicates that the surface and fracture structures of the Buckypaper/polymer composites are even and uniform. What's more, Buckypaper/epoxy composites fabricated by the pressurized infiltration technique possess much higher mechanical properties than that fabricated by the solution soaking technique.
The microstructure of carbon/carbon(C/C) composites with different matrix carbon was studied by polarized light microscopy (PLM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and XRD techniques respectively. PLM results indicate that the different matrix carbon exhibits different optical reactivity, and the average optical reactivity is gradually enhanced from normal pitch carbon, smooth laminar of pyrocarbon, rough laminar of pyrocarbon to mesophase pitch carbon; SEM results show that the normal pitch carbon is mainly of grapy structure, the pyrocarbon exhibits like-crinkle lamellar structure, while the mesophase pitch carbon exhibits lamellar banded structure with different shapes. Under HRTEM, the lattice fringes of the mesophase pitch carbon are arranged regularly, is a long range ordered crystal structure, and the preferred orientation is high. The degree of the graphite and the interlayer spacing of the material B (mesophase pitch-based C/C composites) are better than that of the material D (pyrocarbon-based C/C composites).
High intensity ultrasonic processing is a good way to fabricate nano-composite. In order to study the dispersion process of nano-whiskers under high intensity ultrasonic, numerical and physical simulations of nano-whiskers' dispersion under high intensity ultrasonic were carried out by using glycerol as fluid medium. The numerical simulation results show that ultrasonic forces the fluid to flow along the center line-bottom-wall-center line route and flow velocity is the maximum near the probe tip edge. Besides, the flow velocity increases with the increase of ultrasonic power. The physical simulation results are in good agreement with the numerical simulation results. In addition, cavitation as well as convection is found in the glycerol during the ultrasonic processing; the nano-whiskers are dispersed well in the glycerol under ultrasonic, and the time for fully dispersion decreases with the increase of ultrasonic power.
The 3-D needled C/C preforms with different densities deposited by chemical vapor infiltration (CVI) method were used to fabricate C/C-SiC composites by gaseous silicon infiltration (GSI). The porosity and CVI C thickness of the preforms were studied, and the effects of preform density on the mechanical and thermal properties of C/C-SiC composites were analyzed. The results show that with the increase of preform density, the preform porosity decreases and the CVI C thickness increases from several hundred nanometers to several microns. For the C/C-SiC composites, as the preform density increases, the residual C content increases while the density and residual Si content decreases. The SiC content first keeps at a high level of about 40% (volume fraction), which then quickly reduces. Meanwhile, the mechanical properties increase to the highest values when the preform density is 1.085g/cm3, with the flexure strength up to 308.31MP and fracture toughness up to 11.36MPa·m1/2, which then decrease as the preform density further increases. The thermal conductivity and CTE of the composites, however, decrease with the increase of preform density. It is found that when the preform porosity is too high, sufficient infiltration channels lead to more residual Si, and thinner CVI C thickness results in the severe corrosion of the reinforcing fibers by Si and lower mechanical properties. When the preform porosity is relatively low, the contents of Si and SiC quickly reduce since the infiltration channels are rapidly blocked, resulting in the formation of large closed pores and not high mechanical properties.
Using the Mn-Nb-B low carbon bainite high strength steel with the reducing production technology as the research target, the deformation behavior and phase transformation behavior were studied by the thermal simulation testing machine. Combining with the characteristics of the medium and heavy plate production line, the controlled rolling and controlled cooling technology based on ultra-fast cooling were designed to produce low cost high strength construction machinery steel with superior comprehensive mechanical properties. The strengthening mechanisms such as grain refinement strengthening, precipitation strengthening are effective to produce the Mn-Nb-B low carbon bainite high strength steel. The yield strength and tensile strength of the product reach to 678MPa and 756 MPa respectively, the elongation A50 is 33% and the impact energy at-20℃is 261J. The microstructure of the steel is composed of granular bainite, acicular ferrite and lath bainite. A large number of fine, point, granular M/A constituents and dislocation structures dispersively distributed inside the matrix, and also tiny and dispersed (Nb, Ti) (C, N) precipitates are observed by transmission electron microscopy.
The shell mold-HIP forming process of TC4 pre-alloyed powder was investigated. The shrinkage of the molding part was revealed, and the microstructure and tensile property of the alloy as well as the interface between the alloy and mold were analyzed. Results show that the molding part with complete shape and a relative density of 98% is achieved by mold-HIP forming process. During densification, there is a small amount of shrinkage along the length and width of the molding part, while it is much larger along the depth, which reaches 30% in the centre; the process results in fine uniform basketweave microstructure, with a minority of equiaxed α grains surrounding the lamellar; the plasticity of the shell mold-HIP alloy is more than 1.5 times as much the casting alloy; the ultimate tensile strength of the shell mold-HIP alloy is up to and even higher than the level of the forged alloy. There is no obvious interface reaction between the TC4 alloy and shell mold during the HIP process, while a loose layer of about 10μm is formed on the alloy surface of the part.
A type of low-carbon reduced activation ferritic/martensitic (RAFM) steel is designed.The microstructure and mechanical properties of tested steels prepared by different technologies were investigated by means of scanning electron microscope, transmission electron microscope and tensile test. The chemical composition of precipitations of tested steels are inspected by energy dispersive spectroscopy (EDS), meanwhile the law of precipitation phase of low carbon low activation FM steel was studied by thermodynamic calculations. The results show that the best mechanical properties are obtained by tempering at 750℃for 1h after quenched from heating at 980℃for 1h.The low carbon RAFM steel meeting performance standards can be produced. The precipitations are composed of M23C6 and MX.M23C6 carbide precipitates mainly in the process of below 950℃rolling and heat treatment. However MX mainly precipitates in the process of rolling, and the secondary precipitation seldom occurs during the process of heat treatment and rapid cooling.
The spreading and wetting behavior of Mg-Zn-Al solder under the action of flux and ultrasonic vibration was conducted in atmosphere. The ultrasonic vibration time was 1, 2, 3, 4s, respectively. The spreading morphology and microstructure of the solder was investigated by optical microscope. The results show that the Mg-Zn-Al solder is forced spread under the effect of ultrasonic vibration along the base metal. The impact wave induced by ultrasonic cavitation can break the oxide film on the surface of base metal and the solder, which can promote the solder to wet the base metal. The depth of the dissolved base metal is only 0.12mm. When the ultrasonic time is 2s, the spreading area reaches its maximum. The ultrasonic cavitation can break the columnar crystals of Mg-Zn eutectic phase and the dendrite crystals of α-Mg, which can refine the microstructure of the Mg-Zn-Al solder.
Aluminum alloy anodizing coatings were prepared for LY12CZ in the boric-sulfuric acid solution (45g/L sulfuric acid, 8g/L boric acid) with the addition of 10%, 20%, 30% (volume fraction)silica sol, with the gradient voltage of 15V. The current and voltage transients of the anodizing process were collected by data collection instrument. The surface morphologies, microstructure and chemical composition of the anodic coatings were characterized by scanning electron microscopy (SEM). The corrosion resistance was examined by neutral salt spray, electrochemical impedance spectroscopy (EIS) test and titrating test. The results show that the different concentration of silica sol addition can influence the forming and dissolution of anodizing coatings, improve the compactness smoothness and corrosion resistance during the anodizing process in the boric-sulfuric acid solution.
The iminodiacetic acid chelate fiber(IDACF) which has a property of selective adsorption, was fabricated by amination and carboxylation using chloramethylated polypropylene grafted styrene fiber as raw material. Orthogonal experiment was adopted to study the effect of temperature, time, liquor ratio and the amount of chloroacetic acid on carboxylation reaction. The maximum adsorption capacity of iminodiacetic acid chelate fiber to Cu2+ is 65.54mg·g-1, which is 10.52 times of that of Fe3+. Elementary analysis(EA), Fourier transform infrared spectrum(FT-IR), scanning electron microscopy(SEM) and thermogrametry(TG) were used to characterize the structure and the properties of the iminodiacetic acid chelate fiber. The results show that iminodiacetic acid has been transformed to the raw fiber successfully after amination and carboxymethylation, and IDACF has good thermal stability.
In order to solve the problem of uneven wear of TC bearing that conventional method brought and improve its service life, wear-resistant coating was fabricated on the surface of steel parts matrix with the method of laser additive manufacture. The Cr3C2/Fe based alloy was deposited by laser cladding technique on the inner-sleeve cylindrical and outer-sleeve bore of TC bearing with two different process parameters. The high-performance coating was obtained respectively, of cracks free, no pores and with good metallurgical quality. The morphology of the laser cladding coating was observed by scanning electronic microscope (SEM), the composition was analyzed by EDS, the phase transformation was characterized by XRD. The wear resistance, corrosion resistance and hardness of the laser cladding layer were tested by friction and wear tester, salt spray test chamber and digital micro-hardness tester respectively. The results show that the average micro-hardness of composite coating is HV700. The wear resistance of the composite coating is about 3 times as much as the Ni-based alloy. The corrosion resistance is close to 316L stainless steel.
The Al composites reinforced by carbon nanotubes (CNTs) and Al2O3 particles were fabricated by chemical vapor deposition (CVD) and ball milling method. The effect of milling time and Al2O3 content on the microstructure and mechanical properties of composites was studied. The results show that the uniform dispersion of CNTs and Al2O3 reinforcements in the Al matrix can be achieved by using this method. As the milling time increases, the microhardness of composite increases. When the milling time is 180min, the microhardness of composites reaches 2.1 times of pure Al. In addition, the microhardness and compressive yield stress of CNTs-Al2O3/Al composites both increase as the Al2O3 content increases. When the mass fraction of CNT reaches 4%, the microhardness and compressive yield stress of CNTs-Al2O3/Al composites are 112.1HV and 426MPa, which are the 2.8 and 4.6 times as large as that of pure Al, respectively. The results indicate that the hybrid addition of CNTs and Al2O3 play good synergic enhanced effect.
Uniaxial oriented poly (ethylene chlorotrifluoroethylene) (ECTFE) fibers were prepared by the melt spinning method using ECTFE resin as the fiber-forming polymer. The crystal structures, thermal and mechanical properties and creep resistance of the prepared fibers were analyzed by X-ray diffraction (XRD), differential scanning calorimetry (DSC), mechanical and creep performance testing, etc. Results show that, the uniaxial oriented ECTFE fibers have favourable crystallization property. Their crystalline structures belong to hexagonal system, the degree of crystalline orientation is about 90%. The uniaxial oriented ECTFE fibers have excellent mechanical properties, thermostability, creep resistance and chemical corrosion resistance (such as acid, alkali, strong oxidizing reagents, organic reagents, etc).
In order to investigate the corrosion performance on intersecting and longitudinal surfaces of unoxidized and oxidized directionally solidified superalloys, Ni-base directionally solidified superalloy DZ125 and Co-base directionally solidified superalloy DZ40M were selected. Oxidation behavior on both alloys with different orientations was investigated at 1050℃at different times, simulating the oxidation process of vanes or blades in service; subsequent electrochemical performance in 3.5%NaCl aqueous solution was studied on two orientations of unoxidized and oxidized alloys, simulating the corrosion process of superalloy during downtime. The results show that grain boundaries and sub-boundaries of directionally solidified superalloys are susceptible to corrosion and thus longitudinal surface with lower area fraction of grain boundaries has higher corrosion resistance. Compared to intersecting surface of alloys, the structure of grain boundaries of longitudinal surface is less conducive to diffusion and thus the oxidation rate on longitudinal surface is lower. Formation of oxide layers on alloys after short-time oxidation provides protective effect and enhances the corrosion resistance.
The interfacial shear strengths between two kinds of mesophase pitch-based carbon fibers and epoxy resin matrix were respectively measured by microbond test. The forces when microdebonding occurring between resin microdroplets and carbon fibers were obtained from the load-displacement curve, and the morphologies of debonded microdroplets and carbon fibers were observed by scanning electron microscopy. Then, the average interfacial shear strength, standard deviation and coefficient of variation for samples were quantitatively calculated. Moreover, the relationships between interfacial shear strength and the lengths, diameters of microdroplets, carbon fiber diameter were analyzed. The results show that interfacial shear strength is proportional to the ratio of length-to-diameter of the resin microdroplet, and inversely proportional to the carbon fiber diameter, to the ratio of the microdroplet length-to-carbon fiber diameter, and to the ratio of the microdroplet diameter-to-carbon fiber diameter.
A self-designed oxygen-kerosene ablation system was employed to study the ablation mechanism and performance of the carbon-carbon composites. Particle concentrations of the gas-solid two-phase ablation flow were 0, 1.37%, 2.22%, and 2.64% respectively. The microstructure of post-test samples was analysed through the scanning electron microscope (SEM), and the ablation rate was calculated. The influence principle of particle concentrations on the ablation rate of the carbon-carbon composites was studied, and the mechanism of ablation was analysed. Experiment results show that with no particles involved the mass ablation rate is 0.159g/s and the linear ablation rate is 0.175mm/s, while with particles introduced, the minimum mass ablation rate and linear ablation rate are 0.432g/s and 0.843mm/s respectively, with the increase of particle concentrations, the ablation rate becomes accelerated. Particle erosion makes the ablation of sample seriously intensified, and the ablation gradient of radial fiber on erosion surface is increased with the increase of particle concentrations as well.
The Ti film with special structure was deposited onto glass substrate by magnetron sputtering, then via the process of electrochemical anodization and annealing, a transparent TiO2 nanoporous coating (denoted as TNP) with high photocatalytic activity can be directly formed on glass substrate. The crystal structure of the TNP was detected by X-ray diffractometry (XRD) and the morphology of the coating was observed by scanning electron microscopy (SEM). The transmittance, wettability and adhesion of TNP were investigated by UV-Vis spectrophotometer, contact angle meter and scratch tester respectively. Finally, the photocatalytic activity of TNP was evaluated by degradation of methylene blue solution under UV illumination. The results show that the prepared TNP coating has a nanoporous structure and only anatase can be found after annealing, the transmittance of TNP coating can reach 80% or more in visible region, with a super hydrophilic surface (contact angle < 6°) and the adhesion strength between TNP coating and glass substrate is 2.9N; the degradation rate for methylene blue (C0=1×10-5mol/L) can reach 94% in 2 hours and the photocatalysis reaction rate constant is 1.47h-1.
Through in-situ reduction method, Ag nanoparticles were loaded on the surfaces of EVA composite foams. A series of investigations, including field emission scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction, were carried out to characterize the samples. Thermal stability and antibacterial properties of the products were evaluated by thermo gravimetric analysis and antibacterial test, respectively. Results show that nanoparticles, with an average particle size of 20nm, are elemental silver and decorated on the surface of EVA composite foams in uniform and regular stacks; after the presence of Ag nanoparticles, char yield of the products at 600℃could increase to 3.22%; the samples have good persistent antibacterial effects and after 50 washing cycles, the antibacterial rate reaches above 98% and 99% against escherichia coli and staphylococcus aureus, respectively.
Micro alloy metals P or P/Cu/Zn were added into Sn-Bi alloy to investigate the doping effects on microstructure, mechanical property, deformation fracture from the function of P in pure tin. The results show that doping 1%(mass fraction, same as below) P to pure tin can improve the strength and stiffness, decrease the plasticity. Only 0.1%P additive degenerates the mechanical property of Sn-Bi alloy, this is related to the existing form of element P in the base metal and the microstructure of the base metal. In Sn base alloy, P is distributed in phase or grain boundaries in the form of Sn-P intermetallic compounds (IMC), restricting the diffusion and shifting of deformation. Therefore, Sn-1P alloy, IMC distributed in beta-tin base plays a role of strengthening in pure tin doped situation, in Sn-Bi alloy instead, enhancing the deformation mismatch under loading becoming the weak spots where cracks may initiate and propagate, and leading to brittle fracture. Finally, addition of P/Zn/Cu simultaneously to Sn-Bi alloy, the doping can optimize the microstructure, improve the strength and enhance the ultimate tensile strength (UTS) of Sn-Bi alloys.
Metamaterials, man-made materials, enable us to design our own "atoms", and thereby to create materials with unprecedented effective properties that have not yet been found in nature. Smart metamaterial is one of those that is an intelligent perceptive to the changes from external environments and simultaneously having the capability to respond to thermal and mechanical stimuli. This paper can provide a review on these smart metamaterials in perspective of science, engineering and industrial products. We divide smart metamaterials according to what they are tuning into: optical, mechanical, thermal and coupled smart metamaterials. The rest of two techniques we addressed are modelling/simulation and fabrication/gene engineering. All of these types smart materials presented here are associated with at least five fundamental research: coupled mechanism of multi-physics fields, man-made design for atom/molecular, metamaterials coupled with natural materials, tunability of metamaterials, and mechanism of sensing metamaterials. Therefore, we give a systematic overview of various potential smart metamaterials together with the upcoming challenges in the intriguing and promising research field.
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