- 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 of SiCf/SiC ceramic matrix composites (CMCs) as well as their applications in aero engines has obtained rapid development recently. This is owing to the large quantity of coupon tests performed on various properties of these materials, and the establishment of corresponding databases. Here, the physical and mechanical properties of CMCs developed by SNECMA, NASA and GE were reviewed. The influence of fabrication techniques on the properties of materials were discussed with an emphasis on tensile properties. Meanwhile, the service performances of these materials were summarized, including oxidation, water vapor/oxygen environmental resistance at high temperature, fatigue and creep behaviors, resistance to thermal shock and foreign object damage, along with the mechanism of damage and failure in environments such as heating, loading, water and oxidation. At last, some suggestions about domestic further research on performances testing for SiCf/SiC ceramic matrix composites were proposed.
Traditional electronic strain sensors based on metal and semiconductor materials have poor flexibility and wear-ability, which are not applicable for stretchable sensors. With the development of flexible electronic materials, wearable electronic devices show great market prospects. Flexible strain sensors have many unique advantages, such as good biocompatibility, wearable, stretchability and elasticity, which become a hotspot of research. The research progress is the preparation technology, performance and application of PDMS based piezoresistive and capacitive flexible strain sensors were summarized in this paper. Finally, challenges, important directions and perspectives related to PDMS flexible strain sensors were prospected.
Three-dimensional braided composites have attracted extensive attention due to their excellent mechanical properties, which cannot be separated from their special structures. This paper aimed to provide a review on the research of 3D braided preform forming technology and the microstructure of 3D braided composites. In the aspect of forming technology, braiding methods and equipment currently used were introduced, then, research on new braiding method and braiding process was also introduced. In the aspect of its microstructure, detailed procedures of research from abstract to specification were presented, and the shortcoming of current microstructural model's characterization of fiber bundles deformation was pointed out, and two advanced modeling methods were introduced. Finally, it was pointed out that the methodology to characterize 3D braided structures can be further established in order to explore novel structures. Also, the mechanism of yarn deformation should be studied so as to get the microstructure model which is closer to the reality.
Carbon nanotubes(CNTs) exhibit good mechanical, electrical and thermal properties, and thus with wide application prospects, therefore, attracted wide attention are received from scholars of various countries. CNT fibers and films, composed by CNT bundles, are the main application forms of CNTs in macroscopic scale. However, the performance of CNT fibers and films are far lower than that of single CNT, which is mainly owing to their low density. The main approach for strengthening CNT fibers and films is to improve their density. The progress of CNT fiber and film densification researches in recent years was summarized in this article, and the related theoretical basis of the densification was concluded. The influence of different densification processes on their microstructure was discussed, and the tensile properties and electrical properties were compared. Based on current research situation, the shortage was also pointed out in this article, and the process combining the drawing and rolling was considered to be the effective method for CNT fibers and films strengthening.
Flexible and amorphous silicon carbide micro/nano fibrous mats were prepared by electrospinning technology with polycarbosilane(PCS)as the precursor to prepare PCS micro/nano fibrous mats and followed by cross-linking and high temperature heat treatment process. The silicon carbide micro/nano fibrous mats reinforced silica aerogel composites (silicon carbide/silica aerogel) were prepared by using the SiC as the reinforcing material, and combining the sol-gel and super-critical drying technology. The results show that the average diameter of SiC fiber mats is about 1.7μm, the transverse tensile strength is 0.6MPa, and elongation is 6.0%. SiC micro/nano fibrous mat and SiO2 aerogel matrix have better compatibility, the hydrophobic angle of SiC/SiO2 aerogel composites is 132°, specific surface area is 241.8m2/g and the mean pore diameter is 12.0nm. SiC micro/nano fibrous mats strengthen the toughness of aerogel while maintaining its good thermal insulation and hydrophobic properties.
Under normal temperature and pressure conditions, potassium niobate nanowires with uniform diameter and good crystallinity were prepared by laser-induced method using KOH and Nb2O5 as raw materials. The samples were characterized by XRD, SEM, Raman and UV-Vis, the light absorption and photoluminescence properties of potassium niobate nanowires were studied. The results show that the chemical formula of laser-induced samples is KNb3O8 (the space group is Pmmm (47), which is orthorhombic system). The growth mechanism of nanowires is the SLS mechanism. The band gap of the prepared nanowires is 2.84eV, there is a strong blue emission peak at 436nm.
La doped Bi2WO6 nanomaterials were synthesized by one step hydrothermal method using Bi(NO3)3·5H2O, Na2WO4·2H2O and La(NO3)3·6H2O as the raw materials. The phase composition and optical property of the as-prepared materials were systematically characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy and BET surface area. XRD result reveals that La is doped in Bi2WO6 successfully, and the prepared samples still possess orthorhombic structure. UV-Vis study shows the absorption edge of the prepared samples has a red-shift with the increase of La doping, indicating that La doping can broaden the absorbance range of the La doped Bi2WO6 materials. BET measurement shows that the specific surface area of La doped Bi2WO6 materials is increased with more La doping. In addition, the effect of La doping on the photocatalytic activities of the samples were measured by the degradation of methylene blue (MB). Results show that the best photocatalytic property is found in the 2.0% La doped Bi2WO6 nanomaterial; after 120min of reaction, the degradation rate of MB reaches 91%.
Hierarchical porous carbon foam, using liquid foam as soft template and water-soluble phenolic resin as carbon source and isocyanate as curing agent, was fabricated by microwave activation method. The structure and electrochemical properties of the carbon foam were characterized. The results show that the microwave activation technology can improve the rapid evolution of H2O molecules on the liquid foam film to form a large number of nanopores on the carbon foam wall to lead to the increased specific surface area, but do not change the average pore size. The specific surface area of the activated sample is 378.2m2/g and its specific capacitance at 1A/g current density is 123.7F/g, which is about 94% higher than that of the unactived sample.And the internal resistance of the sample is reduced due to the improvement of the pore structure by microwave activation.
To study the influence of the ratio of active material, conductive agent and binder on performance of lithium-sulfur battery, the cathode active material was prepared by ball milling sublimed sulfur and acetylene black with mass ratio of 7:3, cathode composite materials were prepared with five different proportions of active material, conductive agent and binder, then the structures and morphologies were observed and batteries were resembled and tested. Electrochemical tests show that the first discharge specific capacity of cathode material with proportion of 7:1:2 reaches 1019.0mAh/g in the current discharge rate of 0.15C, and after 100 cycles, the specific capacity reaches 547.9mAh/g with capacity retention rate of 53.7%, indicating the cathode material with this proportion is desirable, which is due to reasonable component ratio making this cathode composite material possess optimum mesoscopic electronic conductivity and macroscopic fastness. This mechanism can also be guidance for adhesion modification of other micro powders.
Nanosized SnO2@BNNSs composites were prepared by the simple and industrializable coprecipitation method. The SnO2 nanoparticles were homogeneous and distributed on BNNSs with diameter at approximately 4-5nm. SnO2@BNNSs@C composite was prepared with glucose as carbon source to improve the electron conductivity. Compared with SnO2 and SnO2@C, the SnO2@BNNSs@C complex has a reversible specific capacity of 490mAh/g after 50 cycles at the current density of 100mA/g, and its efficiency up to 98.8%. The synergistic effect between three components (SnO2, BNNSs, C) is conducive to the improvement of electrochemical performance.
To rapidly prepare the alumina ceramic microspheres with control of particle size, a ceramic microsphere rapid forming equipment based on droplet jetting technology and slurry curing technology was designed. The Al2O3 microspheres were prepared by using the rapid forming device with alumina powder as raw material, polyvinyl alcohol (PVA) as a binder and boric acid as a curing agent. The effect of different slurry composition parameters on the formability of green body was investigated. The effect of nozzle diameter and slurry extrusion pressure on the particle size of Al2O3 microspheres was studied. The effect of sintering temperature on the properties of Al2O3 microspheres was analyzed and compared. The results show that when the mass fraction of alumina powder, PVA and boric acid are respectively 70%, 3% and 10%, the green body of Al2O3 microspheres have high sphericity and better formability. The controllability of the particle size distribution can be achieved by adjusting nozzle size and slurry extrusion pressure. Ceramic microspheres possess the best comprehensive property, when sintered at 1400℃, the particle size of Al2O3 microspheres is uniform, the sphericity is about 1.08, the porosity is 43.7%, the relative density is 82.1%, and the crush load is up to 76.5N.
Polycrystalline cubic boron nitride(PcBN) was prepared under a high temperature and an ultra-high pressure using an in situ synthesis method. The influence of sintering temperature on composition, micro-structure, relative density, porosity and mechanical property of the PcBN was investigated by means of X-ray diffraction(XRD), field scanning electron microscopy(FSEM) and energy dispersive spectroscopy(EDS). The results show that the composition of PcBN is translated from intermediate phases to stable phases consist of TiB2, h(hexagonal) AlN and TiN when increasing the sintering temperature in the range of 1400-1600℃ under ultrahigh pressure of 5.5GPa. The cBN particles connect with each other by the reaction product. With the increase of the sintering temperature, the length of rod-shaped crystals of strengthening phase TiB2 decreases and the pore in surface reduces. There exist the extraction and fracture mechanism of the rod-shaped crystals in the fracture process. The porosity is prominent reducing and the relative density increases when increasing the sintering temperature. With further increasing the sintering temperature to 1600℃, the PcBN exhibits optimal comprehensive mechanical properties with a micro-hardness of 44.1GPa and a flexural strength of 859.3MPa.
In order to improve the high temperature anti-deformability of ceramic shells for single crystal blade, composite modified ceramic shell specimens of Y2O3 and Al-Si-Mg series mineralizer were prepared with addition of 2% (mass fraction, the same below), 4% and 6%, then the thermal expansion and high-temperature self-loaded deformation of specimens were studied. The results show that high temperature thermal expansion and self-loaded deformation firstly reduced and then increased with the increase of the addition, when content is 4%, the test improvement is obtained, the minimum values of the linear expansion and high-temperature self-loaded deformation are 0.66% and 0.55% at 1500℃, and the average decrease efficiency of the composite mineralizer on high-temperature self-loaded deformation is twice that of thermal expansion. The mechanism of composite mineralizer to modify the shell is to prevent the viscous flow of glass phase by bridging mullite as micro framework and fine globular yttrium aluminum garnet (YAG) inserted between crystals, to jointly improve anti-deformation ability of the shell. However, adding too much, it will produce a large number of glass phase, weakening high temperature performance of the shell.
Double disks controller was used to constrain the size of spray plume. The flow field characteristics of the constrained spray technology under different gas inlet pressures were simulated by the computational fluid dynamics (CFD) software "Fluent", and the simulation result was experimentally verified. The results show that with the increase of atomization gas inlet pressure, the speed of reverse gas flow increases, and thus, the temperature of the nozzle tip decreases. In this case, solidification of the melt in the nozzle occurs. When the inlet pressures of the gas and metal are 2.5×105Pa and 2.0×104Pa respectively, the pressure acting on the melt decreases to minimum value of about 8.99×103Pa.At this condition, the molten metal flows out smoothly and no apparent oxidation phenomena appear in the deposition billet. Moreover, the effect of atomization is the best and the width of the deposition billet is exactly consistent with the width of the wheel groove of continuous extrusion machine.
Ni-graphene composite coating was prepared on 45 steel substrates by electro-brush plating. The graphene layers, graphene in the composite coatings, the grain size and morphology of the coatings were characterized by transmission electron microscope(TEM), atomic force microscope(AFM), scanning electron microscope(SEM), energy dispersive spectrometer(EDS), Raman spectrometer, X-ray diffraction(XRD). The hardness of coatings was investigated by microhardness tester. The results show that graphene in Ni-graphene composite coating exists in the form of three(type Ⅰ, type Ⅱ, type Ⅲ), compared with the pure Ni coating, the grain size of Ni-graphene composite coatings reduces; when the content of graphene is 0.5g/L, the quality of Ni-graphene composite coating is best; because of the high hardness of graphene and its fine-grain strengthening effect, the hardness of Ni-graphene composite coating is 15.2% higher than that of pure Ni coating.
The time-temperature-property (TTP) curves of 7050 aluminum alloy die forgings were determined by an interrupted quenching method. The second phase dissolving and precipitation mechanism and the strengthening mechanism were studied by TEM and JMA equation.The results show that the nose temperature and incubation period of TTP curves are 337℃ and 0.7s, with the quenching sensitivity range 270-400℃. Low level of the quenching sensitivity to sort the result followed by high temperature, low temperature, medium temperature; Al3Zr particles are the primary nuclear sites of supersaturated solid solution, whose main precipitate phases are η particles during early isothermal process, with the increase of temperature, the grain boundary becomes narrower; after the holding time is prolonged, needle dispersion S phases are the main precipitates of the alloy in the low temperature range; in the medium and high temperature range, a large number of η particles precipitate and aggregate, accompanied by the decrease of volume fraction of S phases, meanwhile the grain boundary becomes coarser and continuous; with the temperature rising, the size of η particles increases while the amount decreases; the rank of strength levels of precipitation is GP zones and η' phases, needle-like S phases, clubbed η phases.
The effect of different heat treatment processes on the microstructure and mechanical properties of the as-cast Mg-5Sm-0.6Zn-0.5Zr alloy was investigated by orthogonal test. The results show that the as-cast Mg-5Sm-0.6Zn-0.5Zr alloy mainly consists of magnesium matrix (α-Mg) and eutectic second-phase; the order of influence of each factor on the average grain size is:solution time > aging temperature > aging time; the effect order of each factor on the tensile strength of the alloy is:aging temperature > solution time > aging time; the influence order of each factor on the elongation of the alloy after fracture is:solution time > aging temperature > aging time. The optimum heat treatment process with good comprehensive mechanical properties is as follows:the solution temperature is 540℃, the solution time is 12h, the aging temperature is 200℃, the aging time is 10h. The analysis of fracture morphology shows that the fracture mode of the as-cast alloy is quasi-cleavage fracture; the fracture modes of the aged alloys are complex, including quasi-cleavage fracture, cleavage fracture and intergranular fracture.
The effect of twin types in compressed samples on nucleation of grains and texture evolution during static recrystallization was investigated by using electron backscattered diffraction analysis (EBSD). The cylindrical samples were compressed with a strain of 16% at room temperature, followed by annealing after holding at 250℃ for 3min, 20min and 60min, respectively. The results show that only a few recrystallization grains can be found in local regions and first nucleated within the twins after annealing for 3min. Recrystallization process can be completed after annealing for 60min. Further research shows that the {10${\rm{\bar 1}}$1}-{10${\rm{\bar 1}}$2} double twins are the preferred sites for new grains nucleation, while the {10${\rm{\bar 1}}$2} tensile twins are unfavorable for the nucleation of static recrystallization. The misorientation angle distribution between new grains and matrix is around 38° randomly. The grain size can be refined effectively by static recrystallization, and the deformation texture is weakened during annealing.
The effect of different Ti contents on the microstructures and tensile mechanical properties of the hot-extruded Cu-15Ni-8Sn alloys was investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and tensile test. The results show that both ultimate tensile strength and yield strength increase significantly with the increase of Ti content, while elongation decreases. The addition of 0.02% (mass fraction, the same below) Ti facilitates the precipitation of γ-(Cu, Ni)3Sn phase, and thereby leads to a significant refinement of recrystallization grain. When the content of Ti increases to 0.3%, a small quantity of needle-like Ni3Ti phase is formed, which abates the effect of γ precipitates on inhibition of recrystallized grains growth. With the addition of up to 0.5% Ti, a larger amount of Ni3Ti precipitates are formed, which enhance the effect of recrystallized grain refinement; however, a few Ni3Ti precipitates become large and deteriorate the elongation of the alloy. In this study when 0.3% Ti is added, the mechanical properties of the alloy are preferable, where the tensile strength, yield strength and elongation are 875, 713MPa and 24.1% respectively.
Mechanical behavior of 316L austenitic stainless steel with different pre-strains was studied at different temperatures of 293-573K and strain rates of 0.0005-0.01s-1, and the effect of pre-strain on mechanical behavior was investigated. The results show that yield strength of 316L stainless steel increases and elongation decreases evidently with pre-strain, and tensile strength basically remains constant with pre-strain. In addition, strain rate sensitivity, temperature sensitivity and strain hardening of 316L stainless steel are inhibited by pre-strain. The effect of pre-strain on mechanical behavior is related to dislocation accumulation and mechanical twin produced in the pre-strain process. According to the variation rule of mechanical behavior with pre-strain, the constitutive models considering pre-strain including Modified Johnson Cook (MJC) and Modified Zerilli-Armstrong (MZA) were constructed. The comparison of experimental results shows that the predicted results of two modified models are in agreement with the experimental data.
Ultrasonic impact treatment(UIT) was used for surface enhancement of 17CrNiMo6 steel. The effects of UIT time on the hardness, surface residual compressive stress and the surface structure refine ment were analyzed. Microstructure distribution of the structure refined layer was studied. The results show that, unprocessed material surface residual stress is about -223.7MPa, hardness is about 650HV, grain size is about 8-10μm. After UIT for 60s, surface residual compressive stress is about -463.4MPa, grain size is about 1-1.5μm within 5-10μm in depth, the depth of grain refined layer is about 250μm whereas. with UIT for 120s, surface residual compressive stress is about -587.2MPa, grain size is about 200-300nm within 5-10μm in depth, the depth of grain refined layer is about 250μm. Surface plastic deformation is greatly enhanced by ultrasonic impact treatment, high-density dislocation is produced under the high strain rate, high rotational speed and cyclic shear in large size gain, grain boundary density is greatly improved, and dislocation movement and grain rotation is accelerated.
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