- 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)
Using polyimide and aluminum phosphate as binders, the bending strength, thermal mass loss behavior, phase transformation after sintering and microstructure of the specimens were researched, by three point bending strength test, TG-DSC, XRD and SEM method. The results show that the polyimide produces binding effect by melting and crosslinking under 500℃,strength of specimens increases from 3MPa to more than 5MPa;while the strengthening effect vanishes, after polyimide is burned out at about 500℃(heating rate:30℃/h). The three aluminum phosphates (aluminum orthophosphate, aluminum metaphosphate and aluminum dihydrogen phosphate) increase the medium temperature bending strength (from almost zero to 0.2,0.2MPa and 0.8MPa respectively) at 500℃. The strengthening effect of aluminum dihydrogen phosphate is the best, while aluminum orthophosphate and aluminum metaphosphate are equivalent. By infusing with dihydrogen phosphate solution, integral ceramic mold is fabricated successfully without shifting and fracture of cores.
The microstructure evolution of Fe-Mn-Si shape memory alloy in the process of thermal mechanical training was studied through analysis by microscopy, XRD, SEM and TEM. The results show that thermal mechanical training is a repeated transformation process of stress induced γ→ε martensite and its reverse. Before the training, few martensites are observed in the structure. After the training, ε martensites distribute uniformly,in parallel with each other, and less crossover phenomenons.Meanwhile,martensites in crystal structure with martensitic prefer zone orientation.After a lot of training(over five times),a lot of dislocation tangle is formed inside the alloy matrix.
Thermal stability of new style Al-Zn-Mg-Cu aluminum alloy 7D04 was investigated by room temperature mechanical tensile test and TEM analysis. The results show that the microstructures and mechanical properties of 7D04-T7451 keep stable for a long time at 125℃ or below. When the thermal exposure temperature is higher than 150℃, the strength decreases with the increasing of thermal exposure time. The higher thermal exposure temperature, the larger strength drops. When the alloy is exposed at 175℃ for 500h, the yield strength and the tensile strength are 286MPa and 385MPa, drop 38% and 26% respectively. The main mechanism of the strength of 7D04-T7451 aluminum alloy decrease during thermal exposure processing is the coarsening of η' phase and η phase.
Inconel 740 alloy was prepared by electron beam melting(EBM). The microstructure evolution and microhardness variation of the alloy under heat treatment conditions were investigated, the precipitation principle and distribution characteristics of phases during heat treatment process were analyzed. The results indicate that Inconel 740 alloy has a good macrostructure and lower inclusion content, the grain size is about 2mm. The microstructure is austenite with a lot of twin crystals after standard heat treatment, the M23C6 carbides are distributed continuously on the grain boundaries, with G phase and η phase. Lots of spherical and 30nm in size strengthen phase γ' precipitate in the grain. The microhardness of Inconel 740 alloy prepared by electron beam melting with standard heat treatment is about 120HV0.1 higher than the same alloy that made through traditional method.
N-doped ZnO (N-ZnO) was prepared with self-designed high temperature annealing devices in NH3 gas. The relationship between preparation condition, band gap, and photovoltaic conversion efficiency of N-ZnO was investigated. ZnO with different N doping concentration was obtained by varying NH3 gas pressure, annealing temperature, and annealing time. The morphology, structure, chemical compositions and optical property of N-ZnO were characterized by scanning electron microscope(SEM),X-ray diffraction analysis(XRD),X-ray photoelectron spectroscopy(XPS) and UV-visible absorption spectroscopy(UV-vis). The results show that N-ZnO possesses a hexagonal wurtzite structure. N doping effectively leads to narrowing of band gap and a red shift of the absorption edge of ZnO. The photovoltaic conversion efficiency of dye-sensitized solar cell based on N-ZnO photoanode can be improved from 0.34% to 1.02%.
Alumina thin films with different structures were fabricated by one-step anodic oxidation of process on the same aluminum using oxalic acid as electrolyte, keeping a certain angle between the cathode and the anode through adjusting angle of electrolyzer. The microstructure and optical properties of thin films were studied. The results show that two areas with different holes on the same piece of aluminum foil are formed. In the range of visible light, alumina films reveal two different structural colors through controlling the thickness of films. The area ratio of different structural colors is controlled through adjusting the angle of electrolyzer. The thicknesses of the alumina thin films can be adjusted by changing the oxidation time, and then the change of structural colors at different zones can be adjusted. The results of polarization test indicate lights reflected by alumina films are linearly polarized light.
Si/3Al2O3·2SiO2+BSAS(1-xBaO-xSrO-Al2O3-2SiO2,0≤x≤1)/Yb2SiO5 environmental barrier coating(EBC) was prepared, based on Cf/SiC substrate by electron beam physical vapor deposition(EB-PVD)and plasma spraying(PS). High temperature oxidation behavior of EBC was studied at 1400℃ constant temperature environment. The results indicate that the mass loss of Cf/SiC specimens with EBC coating occurs when exposure to 80h under oxidation experimental conditions. Ba and Al contained in the 3Al2O3·2SiO2+BSAS middle layer diffuse outward to Yb2SiO5 top coating, then two new phases of BaO2 and Al2Yb4O9 are formed. The early sintering and volume shrinkage of BSAS at 1400℃, and the residual stresses induced by the mismatch of thermal expansion coefficients among mullite, all are the primary factors leading to the spallation of EBC.
The high density polyethylene(HDPE)/expanded graphite(EG)/paraffin thermal conducting shape-stabilized phase change materials(PCM) was prepared by melt blending method.The leakage rate, microstructure, thermal conductivity and latent heat of the composites were studied. The results show that the HDPE, EG and paraffin could be uniformly mixed. The leakage rate of PCM increases when EG is added, but decreases with the increasing of EG content. When the mass fraction of EG is 15%, the leakage rate of PCM is less than 0.6%. The thermal conductivity of PCM increases with the increasing of EG content. The value of thermal conductivity is 1.265W/(m·K) when the mass fraction of EG is 15%. The latent heat of PCM is not changed with the increasing of the EG content.
The lateral bending model of prepreg was established, based on the mechanical characteristics during automated fiber placement(AFP). The buckling radius was deduced by using the principle of minimum potential energy, Rayleigh-Ritz method and the relevant composite material mechanics. Influence of main process parameters, such as layup temperature, layup pressure, layup speed, prepreg tack, etc, on lateral bending capability was analyzed. The lateral bending experiments indicate its effectiveness,using the AFP lay down prepreg arcs with different radii. The results show that the lateral bending performance of prepreg increases with the increasing of temperature, pressure, and decreasing of speed. And the increasing of prepreg tack can significantly improve the lateral bending performance, which all agree with theoretical prediction well.
Based on the finite element software of ABAQUS, with Hashin damage criteria an effective low-velocity impact model of stiffened composite panel was established. The effects of contact pressure, internal energy and damage dissipation energy on the impact response were analyzed. The results show that the peak of contact pressure moves forward and the different value of internal energy and damage dissipation energy becomes bigger with the increasing of impact energy. Meanwhile, the impact test results indicate that the damage degree is direct proportion with impact energy in the low-velocity impact process. Contrast of damage area between finite element analysis and test indicates that both of them fit better.
The silicone antifouling, coating with hydroxy-terminated polydimethylsiloxane as main film,and with the addition of methyl silicone oil with different molecular weight and different content, was prepared. The results show that water contact angles and diiodomethane contact angles become larger, while surface free energy becomes smaller with decreasing the molecular weight and increasing the content of silicone oil; the elastic modulus of coating becomes lower with reducing the molecular weight and the elastic modulus reaches the mininum while the content of methyl silicone oil is 13%(mass fraction) in part A. The relative adhesion force of biofouling increases with the increasing of molecular weight and reduces with the increasing of content of silicone oil; during the process of coatings immersing in seawater, the-CH3 in silicone oil can take hydrogen bonding effect with H2O molecular, thus results in the range of methyl peak becomes lager in FTIR spectra, and the hydrophobicity of silicone coatings decreases; all coatings are allowed to stand in air for one year, only the non-immersion silicone coating with the addition of methyl silicone oil of 1750 molecular weight are found the exudation of silicone oil and the amount of exudation is proportional to the amount of the addition.
Co-electrodeposited mechanism of the quaternary precursor prepared by cyclic voltammetry was studied. And the annealing phase transition mechanism of synthesized CZTS films was analyzed by XRD,SEM,EDS and Raman technologies. The results show that the concentration of Cu2+ and Sn2+ not only affects the deposition rates of its own, but also influences the deposition rates of other metal elements in the solution, while the concentration of Zn2+ only affects its deposition rate.The quaternary precursors are electro-deposited by atomic layer epitaxy, Cu2+ firstly reduces to Cu on the substrate surface under the negative potential, then reacts with S atoms to forms CuS near the substrate. SnS and ZnS are alternately deposited on the substrate in the same way. The binary precursor sulfides gradually transform into Cu2(3)SnS3(4) and Cu2ZnSnS4 with the increasing annealing temperature. The atom ratio of the quaternary co-electrodeposition Cu2ZnSnS4 films synthesized at 550℃ for 1h is Cu:Zn:Sn:S=23.72:12.22:13.07:50.99. The photocurrent of the synthesized CZTS film reaches about 60nA without bias voltage.
Ca-Si alloys were prepared in molten CaCl2-LiCl(mole ratio of 9:1) with high purity silicon dioxide as raw material, high purity graphite and tungsten as electrode by an electrolysis method.The solar grade silicon(SG-Si) was got after the alloys purified by zone melting process. The alloy and purified production were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM) and inductively coupled plasma mass spectrometry(ICP-MS). The results show that electrolysis product is alloy of calcium and silicon at 850℃ when the cathodic voltage is about 2.6V. After twice zone melting process,the purity of silicon of 85% silicon ingot as-prepared is nearly 99.9999%, complying with the standard of SG-Si.
Silver nanoparticles with average diameter of 20-35nm were prepared by aqueous reduction method, and the influence factors of nanoparticles characteristics, such as reaction temperature and PVP concentration, were investigated during reduction process. The results show that monodispersity of nanoparticles is remarkably improved while unfavorable agglomeration is avoided with the AgNO3/PVP mass ratio of 1:4 at the reaction temperature 30℃,and the average diameter of silver nanoparticles reaches the mininum of 22.4nm. Copper pads with the purity of 99.9% are successfully bonded at 200℃ and under the pressure of 10MPa for 30min,using sintering paste employing fresh silver nanoparticles. Morphology of the bonding joint is analyzed with scanning electron microscope(SEM),the interface is compacted tightly and porous sintering characteristic is confirmed.
High temperature tensile tests of P92 steel were carried out at 600-1300℃ by means of thermal simulation method. The fracture morphology and microstructure near fracture at different tensile temperatures were analyzed by SEM and LSCM, and the mechanical properties of P92 steel were investigated. The results indicate that tensile strength decreases from 467.32MPa to 24.32MPa, and yield strength decreases from 56.88MPa to 1.07MPa. The rupture is mainly ductile rupture with ductile and brittle characteristics co-existing. Dynamic recovery occurs with P92 steel at 600-900℃, and the fracture is mainly dimple.The microstructure near fracture of P92 steel is martensite+residual austenite+M7C3+MC +M23C6+M6C+M3C after cooling down to the room temperature. With the increasing of the temperature, dynamic recrystallization occurs with P92 steel, and the fracture is mainly plastic hole. The microstructure is martensite+residual austenite+MC+M6C carbides.
The three kinds of WC-12Co coatings were sprayed by HVO-AF(high velocity oxygen-air fuel spray)equipment, which temperature can range from 1400℃ to 2800℃, with three different spray parameters of HVOF(high velocity oxygen fuel spray),HVO-AF(high velocity oxygen-air fuel spray) and HVAF(high velocity air fuel spray), respectively. The elastic modulus of the coatings was tested with the method of Knoop, and the microhardness was recorded. The microstructure, chemical composition and the phase composition were studied by SEM,EDS and XRD. The results show that the nano WC-Co coatings are uniform and dense, with low porosity, with greatly improved microhardness and elastic modulus than micro-coating. The average hardness and elastic modulus of nano WC-Co coatings at HVO-AF condition are the highest(1515MPa and 308GPa),while the average hardness and elastic modulus at HVOF and HVAF conditions are 1390MPa, 286GPa and 1469MPa, 270GPa, respectively. Compared with this, the average hardness and elastic modulus of WC-Co micro-coatings at HVO-AF are 1065MPa and 242GPa. The appropriate flame flow temperature at HVO-AF condition can control the decomposition of the WC-12Co powders effectively, so,elastic modulus measured is the highest.
Using SEM and TEM, the effect of 1800℃ annealing on microstructures and properties of 3D braided C/SiC composites was investigated under Ar,fabricated by PIP process. The results show that during 1800℃ annealing, the carbothermic reductions and Si diffusing happen at the interfaces of C/SiC composites, resulting in the chemical bonding between fibers and matrix, and fibers are damaged. After 1800℃ annealing, the C/SiC composites fabricated by PIP process indicate 8% mass loss rate, the mechanical properties sharply decrease over 80%, and the fracture behavior changes from toughness fracture to brittle fracture.
Because friction stir spot welding(FSSW) got more and more attention from researchers worldwide, this paper summarized on FSSW based on the open literatures. The process, microstructural characteristics, mechanical properties and numerical simulations of FSSW were reviewed in detail. And then, the applications of FSSW in aerospace, aviation and automobile fields were summed up. Finally, the current problems and issues in FSSW were discussed.
|
Founded in 1956 (monthly) ISSN 1001-4381 CN 11-1800/TB Sponsored by AECC Beijing Institute of Aeronautical Materials |
