- 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 forming process performance of polyborosilazane as RTM resin was investigated using rheometer, and the green composite preforms were further formed using RTM process, then the Cf/SiBCN ceramic matrix composites were fabricated via repeated impregnation-atmospheric pressure pyrolysis. Furthermore, the effect of RTM forming defects on thickness, density and mechanical properties of ceramic matrix composites was studied in detail. The results show that the polyborosilazane fully meets the requirements of RTM forming process to rheological properties. RTM forming defects will further increase the expansion of composites, and result in the obvious increase of the thickness of composites, meanwhile decrease the density of composites at the stage of pre-impregnation and pyrolysis, and finally the bending strength and modulus of ceramic matrix composites are also slightly decreased.
The formation of serrated grain boundaries as a result of different precipitation behaviors of γ' phases at the grain boundaries in the third generation high-performance nickel-based powder metallurgy superalloy (FGH98I) of very small lattice misfit between the precipitate phases and the matrix was systematically studied under varying heat treatment conditions, using optical microscope, field emission scanning electronic microscope and transmission electronic microscope. The results show that the dominant factor of formation of serrated grain boundaries is that the morphologies of γ' phases precipitate at the grain boundaries are different. The quantity, size and morphology of the γ' phases precipitate at the grain boundaries vary with different solution cooling rates of the heat treatment process, which has a strong influence on the formation of serrated grain boundaries. Amplitudes of the grain boundary serrations are found to decrease from 4.02 μm to 0.63 μm as cooling rates increase from 0.1 ℃/s to 10.8 ℃/s, however, the wavelength of the grain boundary serrations increases as cooling rates increase. Different morphologies and size of γ' phases which grow into morphology of unstable protrusion result in different amplitudes of the grain boundary serrations. Different densities of γ' particles distributing along the grain boundaries by both sides can drive the grain boundaries to move to produce the grain boundaries with small wavy serrations. Different formation modes of serrated grain boundaries are put forward based on our experiment results.
The corrosion behavior of steel with five different Nb content in bottom plate corrosion environment was studied in homemade cargo oil tank corrosion simulation device. The influence of Nb on corrosion behavior of low alloy steel in strong-acid Cl- solution environment was investigated.The results show that in strong-acid Cl- solution environment, as Nb content increases,the corrosion speed first decreases and then goes up, meanwhile, with the increase of Nb content, the grain size of test steel reduces and dislocation density increases and also the proportion of small angle grain boundary increases, the test steel which contains 0.055% Nb has good corrosion resistance performance in strong-acid Cl- solution environment.
Commercial B4C powders (~10μm) were added at a definite depth in the aluminum surface to produce B4C reinforced aluminum matrix composites by friction stir processing (FSP). SEM, EDS, high temperature friction and wear testing machine were used to study the friction and wear properties.The influence of processing method and the environmental temperature on the friction coefficient and wear scar morphologies were analyzed and wear mechanism was discussed.The results show that aluminum matrix composites produced by FSP can significantly improve the wear resistance of as-cast ZL109 Al alloy under high-temperature wear conditions. The composite exhibits better wear resistance and lower friction and wear coefficient. At 100℃, the main wear of the FSPed composite is oxidation and abrasive wear. As the temperature increases to 300℃, the main wear changes from oxidation wear to adhesive wear.
Nano-mullite was synthesized by micro-boiling method using aluminium nitrate and silica sol as raw materials, and the activation energy was studied. Grain size, phase composition and morphology of the mullite were analyzed by means of thermogravimetry-differential scanning calorimeter(TG-DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. The results show that when Al/Si mole ratio is 3:1 in the raw materials, mullite starts forming at 854℃, Al-Si spinel starts transforming into mullite at 920℃, mullitization is completed at 1200℃, and activation energy of mullite synthesis is (634.52±28.90) kJ·mol-1. After mullite is calcined at 1200℃, and the mole fraction of mullite containing Al2O3 is 59.8%, the average particle size is 31.7nm, with needle shape, and with these needle shape mullite forming a continuous network structure. The synthesizing temperature of mullite and activation energy decrease as mole ratio of Al/Si increases. Activation energy of synthesizing mullite decreases to (514.73 ± 14.40) kJ·mol-1 when mole ratio of Al/Si increases to 6:1.
Three corrosion resistance directionally solidified Ni-base superalloys with varying mass fraction of Re (0%, 2% and 3%, respectively) were optimally designed, microstructural evolution during high temperature aging at 900℃ was analyzed and the stress rupture life of three alloys was tested at 980℃/200MPa after different aging time. The results show that the tendency of σ phase precipitating grows and the high temperature rupture performance of the alloy decreases due to the increase of Re content and the aging time. The rafting structure of stress rupture specimen, which is obviously refined with the addition of Re, as Re content increases, the decrease of stress rupture performance becomes smaller.
The PDMDAAC-AGE-MAA/nano-ZnO composite was prepared by dimethyl diallyl ammonium chloride (DMDAAC), allyl glycidyl ether (AGE), methylacrylic acid (MAA) and nano-ZnO via in-situ polymerization. The effect of the dosage of nano-ZnO on the performance of PDMDAAC-AGE-MAA/nano-ZnO composite was investigated, and the composite was characterized by FT-IR, XRD and TEM. Then cotton fabric was treated with PDMDAAC-AGE-MAA/nano-ZnO composite. The results show that when the dosage of nano-ZnO is 0.8%, the stability of PDMDAAC-AGE-MAA/nano-ZnO composite is the best; The characteristic absorption peaks of the epoxy groups and nano-ZnO exist in the PDMDAAC-AGE-MAA/nano-ZnO composite, Nano-ZnO is good dispersion in composite; Compared with the control cotton sample, the cotton treated with the PDMDAAC-AGE-MAA/nano-ZnO composite after 10 times of standard washing shows the precent reduction of antibacterial properties against Escherichia coli(E.coli) and Staphylococcus aureus(S.aureus) is above 80%, and the percent reduction of antibacterial properties against Candida albicans(C.albicans) is above 75%, because of the antibacterial properties of the synergistic effect by nano-ZnO and N+ in the composite.The PDMDAAC-AGE-MAA/nano-ZnO composite is coated on the surface of treated cotton fibers. After standard washing, the elements of Zn and N still remain in the treated cotton samples, the cotton treats with PDMDAAC-AGE-MAA/nano-ZnO composite possesses good washing fastness. Compared with the untreated cotton,the cotton treated with PDMDAAC-AGE-MAA/nano-ZnO composite has no effect on the breaking strength.
Near-isothermal canned forging for molybdenum powder sinter was investigated by using finite element software. The influence of process parameters (temperature, friction coefficient and forging rate) on strain distribution was discussed. The results show that the average equivalent strain increases with the rising of forging temperature, but the corresponding deformation is non-uniform. Average equivalent strain increases with the increase of friction coefficient, meanwhile, the fracture crack easily occurs owing to non-uniform deformation. The effect of forging rate on strain is not obvious. Through analysis on the orthogonal experiment, the effect of temperature on deformation uniformatity is the most remarkable.
The morphology, size, distribution and chemical composition of precipitates and the microstructure of the low carbon bainitic steel with different content of Ti were investigated by field emission scanning electronic microscopy (FE-SEM), high resolution transmission electron microscope(HR-TEM) and energy disperse spectroscopy (EDS). The results show that the test steels holding at 450℃ and 520℃ for 2h, the microstructure of three kinds of steels is granular bainite. Compared with the low titanium steel, the yield strength of the high titanium steel and titanium-vanadium steel increases by over 150MPa.There are two kinds of the nanometer-sized precipitate particles in high titanium steel:one of these is titanium carbide, which size is more than 15nm. The other is composite precipitate with the FCC(face-centered cubic)-(Ti,Mo)C structure, which size is smaller than 10nm. In the matrix of titanium-vanadium steel, there are a great amount of (Ti,V,Mo)C composite precipitates with the size smaller than 10nm.
The casting titanium alloy ZTC4 is widely used in aircraft and aircraft engine. Through in-depth investigation of the total fatigue life prediction methods for ZTC4, the present thesis aims at exploring new ways for damage tolerance design and life prediction of aero's key components. By a combination of macro- and microscopic analysis methods, ZTC4 was studied systematically under constant-amplitude loading with three types of tests, i.e. high-cycle fatigue test of plane specimens, long crack growth test of center crack tensile (CCT) specimens and direct SEM observation. The main causes of fatigue failure, namely material's initial defects (inclusions or pores), were quantitatively characterized. The baseline long crack growth data of ZTC4, (da/dN)-Keff, was generated based on the Newman crack closure model. By fracture mechanics analysis of embedded elliptical cracks, and starting from the initial flaw sizes determined from statistical analysis of the material's microstructure and fractographic observation of fracture surfaces, total fatigue life of ZTC4 under constant-amplitude loading for two stress ratios was predicted and experimentally verified. The good research results with both academic significance and engineering application value are obtained.
Small angle X-ray scattering (SAXS) method was applied to investigate the evolution of microvoids structure during carbonization and graphitization for polyacrylonitrile (PAN) fiber. The SAXS patterns of the PAN based carbon fiber treated by integration are both smooth curves.The scattering signals come from the microvoids structure within fiber. The parameters of the micro-voids structure including mean square radiuses of gyration, relative volume of the microvoids, porosity and specific surface area were calculated. The results indicate that the evolution of the micro-voids structure during carbonization and graphitization can be divided into three stages: 400-700℃, the volume change (mergence of the small microvoids) is faster than the shape change; 700-1800℃, the volume change (split and shrinking of the microvoids) keeps pace with the shape change (complicating of the surface structure); 1800-2400℃, the volume change is slower than the shape change.
The corrosion behavior of X100 steel was studied in simulated solution of Yingtan soil with and without sulfate-reducing bacteria (SRB) by means of mass-loss measurement, linear polarization curves and electrochemical impedance spectroscopy (EIS) techniques,combined with scanning electron microscopy(SEM) and spectroscopy analyzer(EDS). The results show that the corrosion rate with and without SRB with time is:decrease→increase→decrease,the corrosion rate with SRB is less than without SRB,SRB inhibit the corrosion of X100 steel;Corrosion rate is controlled by uniformity and compactness of corrosion product films, Corrosion product film is loose,uneven and less protective in the solution without SRB.In the solution with SRB,however, a compact and homogeneous bonding film is formed on the steel surface, which could suppress the mass transfer so that to mitigate the steel corrosion.Corrosion products are Fe2O3,Fe3O4 and α-FeO(OH) in the solution without SRB,while corrosion products are Fe3O4 and FeS in the solution with SRB.
The influence of stress ratio on the fatigue crack growth (FCG) behaviour of K55 casing-drilling steel was investigated by means of scanning electron microscopy (SEM) and fatigue tests. The results show that stress ratio possesses a remarkable influence on ΔK responding to starting point of crack unstable zone. The FCG rates responding to starting point of crack unstable zone exhibit a significant decrease with the increase of stress ratios, and the FCG threshold value possesses a significant decrease. The average load,which is gradually instead of ΔK, turns into the dominant drive force of the FCG when the fatigue crack propagates into the unstable zone from Paris region bit by bit. The fatigue fracture surface exhibits obviously impact facture characterization, when the crack propagates into overload tensile zone.
Nano-Fe3O4 powder materials were prepared by using chemical co-precipitation method.The structure and properties of nano-Fe3O4 powder with citrate and without citrate were characterized and analyzed by solution adsorption, transmission electron microscopy, X-ray diffraction and Gouy magnetic balance method. The results reveal that: the specific surface area of nano-Fe3O4 powder which prepared by adding citrate is 1.499, grain particle size is 8nm, magnetic susceptibility is 11.6534, smaller particle size, better dispersion and strong magnetic performance.
A huge challenge was presented on mass reduction and noise reduction of the traditional structural material with development of aerospace vehicles toward high-speed, light mass and multi-function, application of the precise electronic equipment and improvement of comfort requirements. In recent years, with the rapid increase of fiber-reinforced composite materials in the application proportion in aerospace, development of the new structure-damping multifunctional materials with both high mechanical properties and high vibration damping performance has become one of the hot topics of research. The damping mechanism of structure-damping composites was described firstly, further the major domestic and international research results of structural damping composites were reviewed, and then its future development trends were discussed, including the development of new multi-purpose damping intercalation materials, the introduction of new damping mechanisms, the development of multi-level structure model and multi-scale simulation of mechanical properties and damping properties.
The characteristics and types of traction motors for hybrid/electrical vehicles and the requirements to non-orientation silicon steel sheets were systematically reviewed. It was summed up that the non-orientation silicon steel sheets, which are suitable for traction motor, not only require high strength, fatigue properties, but also good magnetic properties, i.e. high permeability and low iron loss at high frequency. The specific contents of the relevant patents on the high strength non-orientation silicon steel sheets of the leading Iron and Steel Companies in Japan were introduced comprehensively, and the involved technological routes in the patents were analysized with thermodynamic calculations. It was concluded that precipitation strengthening technological route is the future developing trend. Particulary, Ti precipitation strengthening is not feasible; Nb precipitation strengthening is feasible but the composition and process window is narrow, and must be combined with the solution strengthening of Ni, Mn; while Cu precipitation strengthening process is simple, cost-effective, and practical.
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