- 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)
A solution method for modifying thermoplastic polyurethane (TPU) by the introduction of 3D functionalized nanohybrids composed of two-dimensional GONRs and one-dimensional CNTs was applied. FTIR, XRD, XPS and TEM were employed to characterize the structure and properties of GONRs-CNTs hybrids before and after modification. The functionalized GONRs-CNTs (pGONRs-CNTs)/TPU composite films were subsequently prepared by solution coating method on a coating machine. Furthermore, by means of oxygen transmission rate test, tensile test and the observation of surface morphology, the synergetic effect between GONRs and CNTs and the effect of different pGONRs-CNTs content on the barrier and tensile properties of TPU composite films were also studied. The results show that a unique three-dimensional (3D) crosslinked nanostructure is successfully obtained, in which GONRs are bridged by CNTs. We also find that the as-prepared pGONRs-CNTs with neat shape and low defect are evenly dispersed in TPU matrix and form strong interfacial adhesion with the matrix, while the existing of CNTs play the role of supporting frame to prevent GONRs from sliding and aggregation; modified by phenyl isocyanate, the lipophilicity of pGONRs-CNTs composite is obviously improved, while, by the introduction of huge isocyanate, the interlayer spacing is further improved, which is good for uniform dispersion in the polymer matrix. As a result, when the mass fraction of pGONRs-CNTs is 0.5%, the barrier and tensile properties of pGONRs-CNTs/TPU composite films reach to the optimal values:the oxygen transmission rate decreases by 63.08% and the tensile strength increases by 46.55%, compared with those of the neat TPU, which will lead to great benefit for the barrier and mechanical properties of TPU films.
A new two-dimensional cellular automata and finite difference (CA-FD) model of dendritic growth was improved, which a perturbation function was introduced to control the growth of secondary and tertiary dendrite, the concentration of the solute was clearly defined as the liquid solute concentration and the solid-phase solute concentration in dendrite growth processes, and the eight moore calculations method was used to reduce the anisotropy caused by the shape of the grid in the process of redistribution and diffusion of solute. Single and multi equiaxed dendrites along different preferential direction, single and multi directions of columnar dendrites of Al-4% Cu alloy were simulated, as well as the distribution of liquid solute concentration and solid solute concentration. The simulation results show that the introduced perturbation function can promote the dendrite branching, liquid/solid phase solute calculation model is able to simulate the solute distribution of liquid/solid phase accurately in the process of dendritic growth, and the improved model can realize competitive growth of dendrite in any direction.
The Al-Si-Cu alloy system is considered to be a promising choice of filler metal for aluminium alloys brazing due to its high strength and low melting point. The greatest obstacle is its lack of plastic forming ability and being difficult to be processed by conventional methods. This disadvantage is ascribed to the considerable amount of brittle CuAl2 intermetallic compound which forms when alloy composition is around the ternary eutectic point. In order to overcome this deficiency, authors of this article proposed to synthesize Al-Si-Cu filler metal by using in situ synthesis method, and the structure and properties of brazing joints were studied. The results show that AlSi alloy is used as the wrap layer, and CuAl alloy is used as the powder core in the composite brazing wire, the two alloys have similar melting points. The machinability of the composite brazing wire is much superior to the traditional Al-Si-Cu filler metal. During the induction brazing of 3A21 alloy, when using AlSi-CuAl composite filler wire, AlSi and CuAl alloys melt almost simultaneously, then after short time holding, Al-Si-Cu braze filler is obtained, the brazing seam has uniform composition and good bonding interface, also, the shearing strength of the brazing joints is higher than the joint brazed by conventional Al-Si-Cu filler metal.
The transformation behavior of secondary phases in conventional ingot and ultrasonic ingot during heat-treatment process were investigated by OM, SEM, EDS and DSC. Crystalline phase transition was observed by SEM with in situ heating station. The experiment results indicate that the ultrasonic melt treatment transforms from columnar crystals to equiaxed crystals, and obtains fine and uniform grains. The melting enthalpy of ultrasonic ingot is 4.60J/g, while the melting enthalpy of conventional ingot is 6.52J/g, combined with EDS analysis results, θ phase and T phase are found to be reduced by 29% after ultrasonic melt treatment. The secondary phases in the ingots include θ phase, T phase, Al3Fe phase and Mg2Si phase. θ phase is dissolved into matrix gradually, T phase transforms to S phase and is dissolved into matrix at high peak temperature, Al3Fe phase transforms to Al7Cu2Fe phase at low peak temperature and remains in the ingots, Mg2Si phase changes nothing during DSC analysis process.
In order to study the influence of the angle and arrangement forms of micro-grooves on the tribological performance of the contact surface, the finite element analysis software was used to simulate the grooved textures with different angles and arrangements. The YLP-20 laser processing system was used to process grooved texture on stainless steel disk surfaces, and the Tribometer (UMT-2) was also used to conduct tribological test under the condition of rotation. The results show that the numerical simulation values are basically consistent with experimental results of grooved textures, and the tribological performance of the friction pairs with textures is also improved. The grooved textures with different angles and arrangement forms have different influence on tribological performance of friction pairs. When the friction velocity is less than 300r/min, the parallel texture with 0° has smaller friction coefficients. While the friction velocity is larger than 300r/min, the parallel texture with 90° has a better ability of reducing friction. Therefore, different grooved textures should be chosen according to operation conditions.
A primer of the bismaleimide resin toughened with block copolymer was prepared. The properties of the primer, such as adhesion, pencil hardness, impact resistance, environment resistant, ageing resistant performance and etc. meet the requirements of the technical specifications of GJB1388. The thermal property of the primer was characterized by differential scanning calorimeter (DSC), thermal gravity analysis (TG), and dynamic mechanical analysis (DMA). The results show that the primer possesses good heat resistance, the glass transition temperature of the primer reach 238℃, 5% mass heat lost temperature is 384℃ after 200℃ cured, and the glass transition temperature of the primer reach 268℃, 5% mass heat lost temperature is 407℃ after 230℃ heat treatment respectively. Bonding strength will increase when the bismaleimide primer doubled with bismaleimide film adhesive, when the primer doubled with J-188 bismaleimide film adhesive, peel strength increases to 107%, the room temperature shear strength and high temperature shear strength increase by 10%.The primer can also be used with other bismaleimide film structural adhesives, which are suitable for the bonding between metals or bismaleimide composites with metals.
The microstructure, hardness and the corrosion resistance in 3.5% NaCl solution of the as-cast AlFeCrCoCuZrx(x=0, 0.5, 1) high-entropy alloys were investigated. The results show that typically cast dendrite structure is formed in the alloys. With the increase of Zr addition, phases in the dendrite region change from single BCC structure to two phases, while phase in the interdendrite region is Cu-rich FCC structure and kept unchanged. The hardness of the alloys increases with the increase of Zr addition and hardness AlFeCrCoCuZr alloy reaches the maximum of HV 698. The corrosion resistance of these alloys in 3.5% NaCl solution is better than that of 304L stainless steel, however as the Zr content increases, the corrosion resistance of alloys is degenerated.
The tungsten carbide coating with both high hardness and dense microstructure was prepared by optimizing the detonation gun spraying parameters. The phase identifications and microstructure of the coating were observed and analyzed by optical microscope, X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The results show that with the increase of oxygen-fuel ratio, the hardness and adhesive strength of the coating firstly enhance and then decrease, while porosities firstly decrease and then increase. When the oxygen fuel ratio is too low, slow particle flight speed and insufficient melt are the main reasons for the degradation of the coating compactness and mechanical properties. When the oxygen fuel ratio is too high, particle decarburization and binder phase nonuniform contract in the cooling process are the determining factors to the coating structure and properties. When the oxygen-fuel ratio is 1.15, comprehensive performance of the coating is optimal, and the oxidation and decarburization of the coating can be effectively reduced. The Vickers microhardness HV0.3 of cross-section reaches 1178kg·mm-2, the porosity is 0.86%, and the bonding strength between the coating and substrate is 152MPa.
As-cast microstructures and phase compositions of Mg-3.52Sn-xM and Mg-6.54Sn-xM (M=Al, Zn, Nd, Gd) alloys were investigated by optical microscope, scanning electron microscope and X-ray diffraction. Meanwhile, the tensile mechanical properties were tested. The results show that the coarse dendrite is refined slightly and few block Mg2Sn phase still exists when 0.91% (mass fraction, the same below) Al and 1.03%Zn are added into Mg-3.52Sn alloy, respectively. When 0.92%Nd and 1.10%Gd are added respectively, the dendrite weakens obviously and many small block or fine short rod-shaped compounds Mg-Sn-Nd and Mg-Sn-Gd can be observed. When 0.93%Al and 1.08%Zn are added into Mg-6.54Sn respectively, the dendrite is refined obviously and Mg2Sn phase tending to precipitate in the state of continuous net begins to break slightly. When 0.86%Nd and 0.74%Gd are added respectively, the dendrite weakens significantly and Mg2Sn phase has already broken into small block completely or significantly. Meanwhile, many small block or fine short rod-shaped compounds Mg-Sn-Nd and Mg-Sn-Gd can also be observed. The respective addition of about 1%Al and Zn into the Mg-3.52Sn and Mg-6.54Sn binary alloys respectively can enhance the tensile mechanical properties namely the ambient and elevated temperatures effectively, while the respective addition of about 1%Nd and Gd cannot enhance them effectively, especially for the addition of Nd.
The core-shell carbon microspheres(CMSs)/polyethylene terephthalate(PET) capsule (PCMSs) by in situ polymerization was selected as flame retardant. The flame-retardant PCMSs/PET functional fiber was prepared by melt spinning method. The structure and properties of PET fiber with different mass fractions of flame retardant were characterized by SEM, sound velocimeter, tensile tester and limit oxygen index apparatus. The results show that PCMSs has a good compatibility and dispersion within PET matrix, and the excellent moisture absorption and flame retardant properties of functional PET fiber with smooth surface is obtained when the mass fraction of PCMSs is 0.6%, but the mechanical property of PCMSs/PET fiber with 0.6% PCMSs is a little lower than the PCMSs/PET fiber with 0.2% PCMSs.
7A04 aluminum alloy plate was jointed by submerged friction stir welding(SFSW), and welded joints were treated (Post Weld Heat Treatment, PWHT), and the effect of post weld heat treatment on the microstructure and mechanical properties in SFSW was investigated. The results show that PWHT joints exhibit dispersively distributed fine precipitates phase morphology, are significantly superior than the feature of the small amount of precipitates with dispersed distribution in SFSW joints. Compared with SFSW joints, the mechanical properties of joints are improved significantly by PWHT. The average hardness of the weld joints nugget zone is increased by 39.7HV, and the tensile strength is increased by 67MPa, reaches 96.1% of the base material, strain hardening capacity of the joints is also enhanced, the tensile fracture exhibits mixed fracture feature of microporous polymerization and cleavage.
Zirconia nanoparticles were prepared using ZrOCl2·8H2O and NH3·H2O as raw materials in the lyotropic hexagonal phase consisting of SDS/TritonX-100/H2O. Effects of pH on the phase structure stability of the template were determined. Effect of ZrOCl2 concentration on the size and morphology of zirconia were discussed. Polarizing optical microscopy was applied to investigate the stability of the hexagonal phase. The size and morphology of the nanoparticles were characterized by SEM, TEM and particle size analyzer. The crystalline structure and purity of the sample were characterized by XRD. In addition, the synthetic mechanism of zirconia nanoparticles in the lyotropic hexagonal phase were proposed by FT-IR. The results show that the hexagonal phase is stable in the condition of alkalinity and the hexagonal phase texture disappear in the conditions of acid; the size and morphology of the nanoparticles obtained are greatly affected by concentration of ZrOCl2. Morphology of samples changes from spherical-like particle to cotton-like particle with the increase of the concentration of ZrOCl2; the mechanism analysisresults show that complexation reaction between the precursor of the sample and the template does not occur, and crystal growth and nucleation of the zirconia nanoparticles are limited by a direct template route in the hexagonal phase lyotropic liquid crystal.
The microstructure and property degradation of turbine blades in aircraft engines during service would finally pose threat to service safety. But report on systematic research work about microstructure and property degradation of serviced turbine blades is limited. In this paper, the 2nd stage turbine blade made of wrought Ni-based superalloy GH4033 was taken from an aircraft engine and investigated by metallographic analysis and physical and chemical phase analysis after service exposure for about 1600 engine operating hours (EOH). Microstructural features including grain microstructure, γ+γ' matrix and grain boundary (GB) carbides in different locations of the serviced blade were observed and quantitatively characterized. Vickers hardness and stress rupture tests were also conducted. The microstructure characterization indicates that the degradation in grain size, γ' precipitates and GB carbides is rarely observed in the airfoil. The service temperature is estimated to be lower than 700℃ based on the coarsen of γ' phase. The Vickers hardness and rupture lives of different locations in this blade are similar to those in the shank and met the requirement of Chinese Aeronautical Industry Standard HB/Z 91-1985. Therefore, it is suggested that the service exposure of this blade can be continuously prolonged. This study would be helpful for the evaluation of turbine blade made of wrought superalloys containing low volume fraction of γ' precipitates.
The ZM5 magnesium alloy plates were welded by TIG welding method. The microstructural characteristics and mechanical properties of ZM5 magnesium alloy joint were studied by optical microscopy, microhardness and tensile testers. The results show that the TIG weld joint of ZM5 magnesium alloy is composed of heat affected zone, partially melted zone and weld metal. The heat affected zone is consisted of primary α-Mg phase and eutectic phase that is composed of eutectic α-Mg and eutectic β-Mg17Al12 phase and mainly precipitated at grain boundaries. In the partially melted zone, the eutectic phase is not only increasingly precipitated at grain boundaries, but also dispersed in grains, and the growth of the β-Mg17Al12 phase is obviously observed. The microstructure in the weld is the typical dendritic morphology. The dendrites are considered as primary α-Mg phase, and the interdendritic regions are α+β eutectic phase. The difference in the microstructure of the heat affected zone, partially melted zone and weld results in their various microhardness values, and leads to the smaller tensile strength and ductility in the ZM5 alloy weld joint than parent metal.
Fatigue fracture often occurs because of the corrosion damage to aerospace structural aluminum alloy with holes. Fatigue tests of 7075 aluminum alloy of both unchamfered and chamfered double-hole specimens under uncorrosion and 24h pre-corrosion were carried out. The influence of both pre-corrosion damage and orifice chamferer on fatigue properties and the differences of fatigue fracture characteristics were analyzed. The results show that the effect on fatigue life of pre-corrosion damage is significant. Median fatigue lives of both unchamfered and chamfered double-hole specimens under 24h pre-corrosion decrease about 31.74% and 26.92% compared with uncorrosion specimens. The orifice chamferer have a certain effect on fatigue life of both uncorrosion and 24h pre-corrosion specimens, with median fatigue lives decreased about 28.02% and 15.36% compared with unchamfered specimens, the main reason is due to the stress concentration after orifice chamfered, on the other hand, cutting marks lead to pre-damage during the orifice chamfering process which will result in an increase of the fatigue crack initiation sites and the fracture probability.
Using Ti(OC4H9)4 as precursor, CO(NH2)2 as nitrogen source, tourmaline as support, the nitrogen-doped nano TiO2/tourmaline composites were synthesized by sol-gel method with ultrasound assisted.The structure and performance of composites were characterized by XRD, FT-IR, UV-Vis DRS, SEM, EDS.The effects of calcining temperature, nitrogen-doped content, tourmaline amount, catalyst system on the photocatalytic activity of nitrogen-doped nano TiO2/tourmaline composites were studied.The results show that the photocatalytic activity of nitrogen-doped nano TiO2/tourmaline composites calcined under 500℃, the nitrogen doped amount of 5% (mole fraction), tourmaline added in an amount of 10% (mass fraction), catalyst dosage of 3g/L, under 500W UV light irradiation conditions, the photocatalytic degradation effect of TNT(10mg/L) is the best, and has a good recycling performance.
Two different types of agglomerate and angular WC/Ni matrix composite coatings were deposited by laser cladding. The high temperature wear resistance of these composite coatings was tested with a ring-on-disc MMG-10 apparatus. The morphologies of the worn surfaces were observed using a scanning electron microscopy (SEM) equipped with an energy dispersive spectroscopy (EDS) for elemental composition. The results show that the high temperature wear resistance of the laser clad WC/Ni-based composite coatings is improved significantly with WC mass fraction increasing. The 60% agglomerate WC/Ni composite coating has optimal high temperature wear resistance. High temperature wear mechanism of 60% WC/Ni composite coating is from abrasive wear of low temperature into composite function of the oxidation wear and abrasive wear.
Carbon nanotubes-alumina (CNTs-Al2O3) porous composite with high porosity and excellent compressive strength was prepared by ice-template technique. Effects of different CNT concentrations on microstructure and properties of the composite were investigated intensively by SEM, XRD and Raman. The results show that the bulk density, porosity and compressive strength of the composite will change with the increase of CNT content. Adding appropriate amount of CNTs will be able to increase the density of ceramic lamellae and enhance the compressive strength of the composite. However, excessive CNTs adversely will decrease the density and compressive strength of material due to the micro pores caused by CNT agglomerations anchored on the internal wall of porous ceramic. The composite reaches a maximum compressive strength of 4.52MPa when additive amount of CNTs at 2.0%(mass fraction), which increases by 66% comparing to pure Al2O3 porous ceramic.
Traditional sealing glasses, which contain heavy metal Pb, posing threat to humans and environment, have been restricted or forbidden by most countries. Therefore, lead-free of low-melting sealing glasses will be the main future development direction. This article based on lead-free of low-melting sealing glasses, the main properties of low-melting sealing glasses were summarized. First, the composition, structural characteristics, performance and research status of several main low-melting sealing glasses, such as phosphate glass, borate glass, vanadate glass and bismuthate glass were introduced. Second, the low temperature and lead-free development directions were put forward. At last, regarding the shortcomings in the research of low-melting sealing glasses, it was pointed out that the future focused breaking points for research are composite doping modification, theoretical research on glass and new technology development of glass preparation.
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