- 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 new method is proposed to evaluate the process parameters by the solid-liquid interface position, thermal gradient angle and the axial thermal gradient. The effects of the process parameters on the solid-liquid interface position, thermal gradient angle and the axial thermal gradient were simulated by ProCAST using LMC (Liquid Metal Cooling) and HRS (High Rate Solidification) processes. The results show that HRS process is little affected by the mold thickness, the dominant heat transfer factor in HRS is radiation from the mold surface, and the dominant heat transfer factor in LMC either mold thermal conductivity or mold-metal interface heat transfer; increasing furnace temperature is beneficial to increase the axial thermal gradient; the withdrawal rate is the most important process parameter which significantly affects the thermal field during solidification, as the withdrawal rate increases, the axial thermal gradient first increases and then decreases, therefore, it is necessary to apply different withdrawal rates for different alloys. After holding 10min at different pouring temperatures, a uniform temperature is achieved, and it has slight influence on the subsequent solidification. It has been put forward that the solid-liquid interface position, thermal gradient angle and the axial thermal gradient can be utilized as a serial of efficient analysis standards for optimization of process conditions independent of casting geometry.
The elevated temperature mechanical properties and fracture mechanisms of as-aged ZM61-xSn (x=0, 6, 8, 10, mass fraction/%) alloys are investigated by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and high temperature tensile test. The results show that the phase compositions of ZM61-xSn (x=6, 8, 10) alloys are α-Mg, α-Mn, MgZn2 and Mg2Sn phases. The Sn element can refine the microstructure, improve the high temperature tensile strength, but deteriorate the elongation of ZM61 alloy. The ultimate tensile strength of ZM61-xSn (x=6, 8, 10) alloys with tensile test at 300℃ are 149, 140, 145MPa, compared with ZM61 alloy which is carried out tensile test at the same temperature, the tensile strength increased 26%, 17% and 23%, respectively. The elongation of ZM61-xSn (x=0, 6, 8, 10) alloys with tensile test at 300℃ are 39.95%, 5.65%, 7.01% and 6.33%. The tensile temperature exerts dominating effect for ZM61-xSn (x=6, 8, 10) alloys on the fracture mechanism. As tensile temperature lower than 220℃, the alloys show transgranular fracture characteristics. The alloys show intergranular fracture characteristics when the tensile temperature is higher than 220℃.
In order to improve the efficiency of turbine blade repairing, protection processes of non-machined surface in Electrochemical Machining (ECM) based on blade repairing were studied. Mathematical model of electric field was developed to obtain current density distribution on anode surface, and to study the repairing principle and consequently analyze the defects forming mechanism by conventional electrolytic repair process. Sacrificial layer process was proposed to protect the non-machined surface in this work and an experimental system was developed to shape overlay welded TC4 blades. The results show that directly shaping process and insulated layer process produce stray dissolution and "stair" defects respectively, while sacrificial layer process achieves acceptable machining performance. With shaping time of 60s, the efficiency is improved; shaped blades have higher precision and surface roughness is Ra≤0.6μm, and with higher repeatability, the design requirements can be met.
Three alloys with different microstructure characteristics were prepared, which microstructures were characterized as enriched with eutectics, supersaturated solid solution and coarse precipitates. Combined isothermal hot compression test and microstructure observation, the hot deformation behaviors of three alloys were studied in the temperature range of 340-490℃ and strain rate range of 0.001-10s-1. The results show initial microstructure characteristics have significant influences on the hot deformation of alloys. Among three alloys, the alloy enriched with coarse precipitates has the largest peak stress value while the alloy enriched with eutectics has the smallest one. The flow behaviors of three alloys were described by the hyperbolic sine constitutive equations. The deformation activation energy for three alloys calculated to be 178.6, 222.1, 154.9kJ/mol, respectively. The processing maps were calculated and analyzed according to the dynamic materials model. Among three alloys, the alloy enriched with coarse precipitates has the widest processing range while the alloy enriched with eutectics has the narrowest one.
The bisphenol A epoxy resin (E-51)/4, 4'-diaminodiphenyl sulfone (DDS) was modified by the epoxy silsesquioxane (EPb-POSS), which was synthesized by hydrolytic condensation of (γ-glycidoxypropyl) trimethoxysilane under basic condition, to prepare EPb-POSS/E-51/DDS modified resin systems. The curing process and the influence of EPb-POSS with different contents on the mechanical properties and thermal stability of the modified resin systems was studied. The results show that although the EPb-POSS have little effect on the curing process and the stiffness of the modified resin, it can significantly improve the toughness; when the mass fraction of EPb-POSS is 1.0%, the impact strength of the modified resin can reach 49.2kJ·m2, is increased by 90.0%, and shows obvious toughness fracture; the bending strength is 132.8MPa, is slightly increased; and the initial decomposition temperature is 378.0℃, is increased by 26.0℃.
Tension-shear test was carried out on middle temperature self-brazing aluminum honeycomb cores after high temperature aging by micro mechanical test system, and the microstructure and component of the joints were observed and analyzed using scanning electron microscopy and energy dispersive spectroscopy to study the relationship between brazing seam microstructure, component and high temperature aging properties. Results show that the tensile-shear strength of aluminum honeycomb core joints brazed by 1060 aluminum foil and aluminum composite brazing plate after high temperature aging (200℃/12h, 200℃/24h, 200℃/36h) is similar to that of as-welded joints, and the weak part of the joint is the base metal which is near the brazing joint. The observation and analysis of the aluminum honeycomb core microstructure and component show that the component of Zn, Sn at brazing seam is not much affected and no compound phase formed after high temperature aging; therefore, the main reason for good high temperature aging performance of self-brazing aluminum honeycomb core is that no obvious change of brazing seam microstructure and component occurs.
CoNiCrAlY coatings were prepared by cold spray process. After deposition, the pre-oxidation treatment of the coating was performed by vacuum heat-treatment. The microstructure and phase constituent of coating were characterized by XRD, SEM and EDS. The hot corrosion behavior of as-sprayed and pre-oxidized CoNiCrAlY coatings in molten Na2SO4 at 900℃ was also studied. The results show that the as-sprayed coating presents a dense structure with low porosity (less than 0.28%, volume fraction) and low oxygen content (0.12%, mass fraction). Vacuum pre-oxidation treatment forms a continuous and dense α-Al2O3 layer on the coating surface, with an average thickness of about 0.26μm. As-sprayed and pre-oxidized coatings can protect the substrate from hot corrosion due to the formation of a continuous and dense α-Al2O3 layer. Moreover, the vacuum pre-oxidation treatment can alleviate the diffusion of S and O into coating, and thus the hot corrosion resistance of coating is improved. The damage of hot corrosion plays a more important role than high temperature oxidation. When corrosion in single Na2SO4 molten salt with the same temperature, the consumption speed of Al is two times of that in high temperate oxidation
A novel composite phase change materials (PCMs) of paraffin/TiO2/active-carbon was prepared by a microemulsion method, where paraffin acted as a PCM and titanium dioxide (TiO2) as matrix material, and a small amount of active carbon was added to improve the thermal conductivity. The compositions, morphology and thermal properties of the paraffin/TiO2/active-carbon composite PCMs were characterized by XRD, SEM, TGA and DSC respectively. The shape stability during phase change process of this composite was also tested. The results show that paraffin is well encapsulated by TiO2 matrix, and thus exhibiting excellent shape-stabilized phase change feature. Besides, this composite PCM also presents superhydrophobic property. Therefore, these multifunctional features will endow PCMs with important application potential in energy efficient buildings.
Silver doped PAN-based hollow carbon nanofibers were prepared combining co-electrospinning with in situ reduction technique subsequently heat treatment to improve the electrochemical performances of carbon based supercapacitor electrodes. The morphology, structure and electrochemical performances of the resulted nanofiber were studied. The results show that the silver nanoparticles can be doped on the surface of hollow carbon nanofibers and the addition of silver favors the improvement of the electrochemical performances, exhibiting the enhanced reversibility of electrode reaction and the capacitance and the reduced charge transfer impedance.
The poly (lactic acid) (PLA) hybrid composites consisted of ultra-fine barium sulfate (BaSO4) and light calcium carbonate (CaCO3) inorganic particles were fabricated via molten blending and compression molding. The effect of BaSO4 mass fraction on the morphologies, mechanical properties, and melt flow rate (MFR) as well as thermal stability of hybrid composites were investigated, under the condition of fixed content of CaCO3. Results show that adequate BaSO4 is dispersed homogenously in the matrix and the inorganic particle-PLA interfacial adhesion is well. PLA is synergistically toughened significantly by BaSO4. With 15% content of BaSO4, the impact toughness and breaking elongation of the PLA hybrid composites are increased by 60.38% and 151.90%, respectively, compared to PLA/CaCO3 sample. As BaSO4 increases, the tensile strength decreases monotonically, while the elastic modulus of samples increases. On the whole, the melt flow rate of the composites is decreased with the presence of BaSO4. However, little effect of BaSO4 on the thermal behavior of PLA is observed.
In order to guide a reasonable application of the bulk ultrafine-grained industrial pure iron, a serious of ultrafine-grained pure iron samples with different microstructures were fabricated by multi-passes ECAP and heat-treatment, and their microstructures and pitting corrosion behaviour were investigated by transmission electron microscopy (TEM), electrochemical polarization and impedance spectroscopy (EIS) techniques, respectively. Results show that:with the increase of ECAP passes, lath-shaped structure with high dislocation density transforms into equiaxed grains with low dislocation density; the dislocation density decreases and the high-angle grain boundaries increase, after the annealing treatment. ECAP passes have less effect on the self-passivation of pure iron, and its open circuit potential (OCP) and polarization resistance are less changed; the pitting corrosion resistance of the ECAPed pure iron is related to the ECAP passes:the pitting potential first decreases and then increases with the increase of ECAP passes; the self-passivation property and pitting corrosion resistance of the ECAPed pure iron are improved after the annealing heat-treatment, the OCP, polarization resistance and pitting potential values increase obviously.
Pure phase spinel ferrite nanoparticles (Mn0.5Zn0.5Fe2O4) were one-step synthesized by the sol-gel auto-combustion method at low temperature. The structural characteristics, morphology and thermal decomposition were characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), TG-DSC analyzer, respectively. The results indicate that pure phase Mn0.5Zn0.5Fe2O4 ferrite nanoparticles of about 60nm in diameter can be directly synthesized after auto-combustion of the nitrate-citrate xerogel under the conditions of pH=7.0, R=1:1 and C(CA)=0.7 mol/L. The obtained nanoparticles show the diameter increases and the diffraction peak narrows but the strength increases after calcined at 400℃ which improves the crystal structure.
The tension-compression fatigue behavior for needled C/SiC composite at room temperature was studied and compared with the properties under tension-tension fatigue loading. The results show that the tension-compression fatigue strength of the needled C/SiC composites is slightly lower than that under tension-tension loading. Hysteresis phenomenon can be observed under both loading stations. The loops move to the right and their slopes and areas increase as the cycles increase. The microstructure of the composites and the morphology of the fractured surfaces of the failure specimens can be observed by SEM. It shows that in addition to the matrix cracking and interface debonding, which is vertical to the loading direction, the meso failure mechanism under tension-compression cyclic loading also includes matrix cracking and interlayer delamination parallel to loading direction, which can make the stress state within fibers worse and finally weakens the fatigue strength of needled C/SiC composites under tension-compression loading.
The influence of water temperature on composite moisture absorption parameters was investigated in temperature-controlled water bath. Experiments of carbon fiber/bismaleimide resin composites immersed in water of 60℃, 70℃and 80℃ were developed respectively. According to the moisture content-time curves obtained from the experimental results, the diffusion coefficient and the balanced moisture content of the composites immersed in different water temperature could be calculated. What's more, the effect of water temperature on the diffusion coefficient and the balanced moisture content were discussed too. According to the Arrhenius equation and the law of Fick, a moisture absorption model was proposed to simulate the hygroscopic behaviour of the composite laminates immersed in different water temperature which can predict the absorption rate of water of the composites immersed in distilled water of 95℃ at any time precisely and can calculate how long it will take to reach the specific absorption rate.
Based on the discussion of the factors influencing the nonlinear ultrasonic testing, the feasibility of nondestructive evaluation of HR3C fireside corrosion was investigated using nonlinear ultrasonic testing. The results show that the number of pulse string is no more than 2df/c and the installation of Hanning window is helpful to reduce the disturbance of the system, in addition, the rough surface of the sample has a significant impact on the nonlinear parameter β. The nonlinear coefficient demonstrates a phased growth trend as corrosion time prolongs. At the initial stage of corrosion (within 50h), there are small increments within 20% in the nonlinear coefficient, however, the nonlinear coefficient β is increased obviously with the duration time to 150h. Compared with un-corroded sample, the amplification in the sample corroded for 200h reaches to 260%. The monotonous varieties in nonlinear coefficient are consistent with the aggravation of corrosion damage, hence, it is feasible to nondestructively evaluate HR3C fireside corrosion by means of ultrasonic nonlinear testing.
g-C3N4/NiO composites were prepared by a simple mixing-calcination method. The structure and morphology of g-C3N4/NiO were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared Spectrometer (FT-IR), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray spectroscopy (EDS). The catalytic effect of g-C3N4/NiO on thermal decomposition of ammonium perchlorate (AP) was investigated by Differential Thermal Analysis (DTA) and Thermo Gravimetric Analysis (TG). The results show that nanometer NiO is uniformly dispersed on the surface of g-C3N4, g-C3N4/NiO composites make the two decomposition peaks of AP combine and the high-temperature decomposition peak value of AP decrease by 62.5℃, which exhibits good catalytic performance. The catalytic activity of g-C3N4/NiO is much higher than that of single-phase g-C3N4 and NiO, clearly demonstrating a synergistic effect between g-C3N4 and NiO.
The K2Ti6O13 whisker separate-doped and K2Ti6O13 whisker and Ni powder multi-doped MgH2 hydrogen storage composite systems were prepared by mechanical milling method. The microstructures and dehydrogenation properties of the prepared samples were characterized by some testing methods such as X-ray diffraction (XRD), scanning electron microscope (SEM) and differential scanning calorimeter (DSC). The results show that the K2Ti6O13 whisker not only plays the roles in refining the MgH2 crystalline grain, but also inhibit the agglomeration of MgH2 particles in K2Ti6O13 whisker separate-doped system, which results in the decreased dehydrogenation temperature of MgH2 matrix. When the mass ratio of K2Ti6O13 to MgH2 is 3:7, the improvement effect on dehydrogenation properties of MgH2 is the most remarkable. As compared with pure ball-milled MgH2, the dehydrogenation temperature of MgH2 in K2Ti6O13 whisker separate-doped system is decreased by nearly 75℃. For K2Ti6O13 whisker and Ni powder multi-dopedsystem, the dehydrogenation temperature of MgH2 matrix is further decreased compared to K2Ti6O13 whisker separate-doped one due to the dual effects of refined MgH2 crystalline grain by K2Ti6O13 whisker and destabilized MgH2 lattice by Ni solution. As compared with pure ball-milled MgH2, the dehydrogenation temperature of MgH2 in K2Ti6O13 whisker and Ni powder multi-doped system is decreased by nearly 87℃.
Transverse fracture often occurs early in the loading history and is one of the key issues limiting the composite structural design. However, the mechanical behavior under transverse loading can not be represented by traditional micromechanical model which does not consider the influence of constituent properties, fiber volume fraction and fiber distribution. A new computational micromechanics finite element method, which the microstructure was idealized as a random dispersion of parallel fibers embedded in the polymeric matrix using improved random sequence absorption algorithm, was presented. The plasticity of matrix and interface decohesion of the composite were included in this model and the residual stress caused by the cooling of composite after the curing process was also taken into consideration. The transverse tension, compression and shear of composite were analyzed by the micromechanical finite element method. Compared with the experiment results, the prediction errors of transverse module were less than 7%, and the transverse compression strength and shear strength were less than 8%. The results demonstrate that the method proposed here can be used to predict the composite transverse behavior.
The modified graphene oxide (DD-GO) was reacted by the Didodecyldimethylammonium bromide (DDAB) and graphene oxide, and then reduced via L-ascorbic acid to obtain functional graphene (DD-RGO). Functional graphene (DD-RGO)/thermoplastic polyurethane (TPU) composite films were prepared by solution on the coating machine. The morphology and properties of DD-RGO/TPU composite films were investigated by FTIR, XRD, FE-SEM, oxygen transmission rate tester and high resistance meter. The results show that DD-RGO with fold layer structure is evenly dispersed in TPU matrix, and the thermal stability, barrier properties and antistatic properties of TPU composite film have been significantly improved. When the mass fraction of DD-RGO is 2%, compared with the pure TPU film, the oxygen transmission rate has been reduced by 50% and the volume resistivity has been increased by 7 orders of magnitude. The barrier properties and antistatic properties of composite films have been improved significantly.
Electromagnetic response of metamaterials is not only determined by its component materials but also the microstructure and arrangements of its resonant elements. The perfect absorber prepared by metamaterial (PMA) can realize 100% absorption in specific frequency bands by designing reasonable structures of resonators. PMA can be applied in many domains, such as stealth material, frequency selective surface, terahertz imaging, micro antenna, intelligent communication, detection and regulation of electromagnetic wave because of its flexible designing, adjustable response, strong absorption, broad band, thin thickness, light mass. Based on the present study situation at home and abroad, we summarized the development, structure, preparation and test of PMA. In order to gain a more profound and comprehensive understanding on PMA, we also explored its trends, prospects and urgent problems. Proactive and intelligent PMA with multi functions and new PMA prepared by new material and new process are the future development trends.
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