- 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)
In-situ tracking on grain orientation evolution of AZ31 Mg alloy rolled sheet during tension along rolling direction at room temperature was conducted by the electron backscatter diffraction technique, and activations of slip systems and twinning during former deformation were analyzed. Analysis results show that, former deformation is accomplished mainly by 〈a〉 basal and prismatic slip activations, and there are not obvious changes for grain orientation, numerous 〈a〉 dislocation slip activations obviously increase the percentage of low angle grain boundaries. For extension twins within grain, they are activated in the process of specimen tension, but not in the process of unloading after tension.
Bonded NdFeB/Sr-ferrite hybrid magnets were synthesized by using warm flow compaction(WFC) technique, and the influences of WFC parameters on the magnetic properties were investigated. The results show that the magnetic properties firstly increase and then decrease with the increase of temperature, pressure and time. The selection of parameters for WFC process is associated with the selected binder. When the epoxy phenolic resin BPANE8200 is used as binder, the optimum process parameters of WFC are 77℃, with loading of 900MPa, and holding time for 8min. The values of remanence Br, intrinsic coercive force Hcj and maximum energy product(BH)max of the hybrid magnets are all obtained the maximum, that is, Br=522mT, Hcj=740.48kA/m,(BH)max=39.82kJ/m3.
Core-shell structured polymer microsphere fabricated via seeded emulsion polymerization, taking methacrylic acid and methacrylate as nuclear monomer, styrene as shell monomer. Hollow polymer microsphere was prepared using the method of stepwise alkali/acid treatment, nuclear layer that containing rich carboxylic acid was fully ionized and moved away from the microsphere via swelling. The finial particle size of the hollow microsphere were controlled through adjusting the amount of emulsifier in the seed preparation stage, and two different size of hollow microsphere(551nm and 156nm) were gotten. The polysulfide sealant was prepared by blending the two kinds of microsphere with polysulfide rubber respectively and the property of the sealant was investigated. The structural characteristics, morphology, ingredients and mechanical properties were analyzed by transmission electron microscope(TEM), Fourier infrared spectrometer(FTIR), electronic tensile machine. The results show that hollow microspheres have a uniform distribution of particle size and high degree of hollowness. The addition of hollow polymer microsphere can reduce the density of the sealant, as well as improve mechanical properties. In comparison, hollow polymer microsphere with big size has a better filling effect.
Aluminum matrix composites reinforced by different contents of multi-walled carbon nanotubes(MWCNTs) were fabricated by friction stir processing(FSP), and their high temperature mechanical properties and strengthening mechanism were studied. The results indicate that by adding MWCNTs, the microstructure of the composites becomes finer, and a small amount of nanocrystals and tangled dislocations are brought into the aluminum matrix. Compared with the aluminum matrix, the strength of the composites at high temperature is enhanced significantly through adding MWCNTs. The strength of the composites is improved gradually, as the MWCNTs content increases, on the contrary, the plasticity of the composites decreases constantly. When the test temperature is 350℃, the tensile strength of 6.6%(volume fraction) MWCNTs/Al composite is up to 78MPa, which is 3.9 times of aluminum matrix without adding MWCNTs. The dimples of composites fracture gradually decreases, exhibits brittle fracture, as the testing temperature increases.
The quality of spot welding joint in 1mm SUS304 austenitic stainless steel sheet was evaluated by using ultrasonic water immersion focusing method. The features of the ultrasonic C-scan image and nugget diameters were analyzed under different welding process parameters. Furthermore, the tensile-shear tests were carried out to examine the mechanical behavior of sport welding joint.The results show that the C-scan image can effectively get nugget diameter from the inner pattern of the spot welding joint based on ultrasonic water immersion focusing C-scan method. The measured nugget diameter is range from 4.76mm to 5.25mm, and it is 2.6%-5.3% larger than inspection diameter. When the welding current is changed from 4kA to 8kA, the failure load average increases from 7116.8N to 9707.1N and energy absorption value increases from 66.3J to 196J. And the nugget diameter of the ultrasonic C-scan image increases from 4.76mm to 5.11mm, too. When the welding current is added to 9kA, the failure strength decreases to 6799.5N and energy absorption value decreases to 41.3J rapidly, it can get the information which includes splash, solder to wear and other weld defects from the ultrasonic C-scan image.
Low carbon Si-Mn steel was processed through the processes of intercritical annealing, quenching(I&Q), or the intercritical annealing, subsequent austenitizing, then quenching partition(I&Q&P) and the austenitizing, quenching partition(Q&P). The C, Mn partitioning behavior and their comprehensive effect on retained austenite were studied by means of electron microprobe analysis(EMPA), field emission scanning electron microscopy(SEM) and X-ray diffraction(XRD). The results show that the microstructure of low carbon Si-Mn steel is composed of martensite, ferrite and some retained austenite after treated by I&Q process. C, Mn in martensite of low carbon Si-Mn steel is enriched, and C enrichment level is higher than Mn level. After treated by I&Q&P process, C, Mn of steel exhibits nonuniform distribution in lath martensite, and the local enrichment of C is more obvious. The martensite can be divided into three forms of "high C high Mn", "high C low Mn" and "low C low Mn" according to the different C and Mn contents. The content of retained austenite of the steel treated by I&Q&P process is higher under the comprehensive effect of C, Mn partitioning than that of Q&P process which is stabilized only by C partitioning.
Solid state shear milling(S3M) followed by melt mixing process was applied to prepare linear low-density polyethylene(LLDPE)/aluminum(Al) composites with high performance. The morphological change of Al particulates during S3M was characterized by scanning electron microscope(SEM) and laser scattering particle analyzer. The thermal conductivity, mechanical properties and thermal stability of the LLDPE/Al composites were investigated. The results indicate that, under the complex combination of shearing, compression, stretching and friction actions, the spherical Al particulates are squeezed into flakes during compounding with LLDPE by S3M, and their dispersion and interfacial adhesion are improved as well, leading to significance properties enhancement of the resulting composites. At 80%(mass fraction) filler loading, thermal conductivity of the composite prepared by S3M for 10 cycles is as high as 8.782W·m-1·K-1, and the tensile strength and flexural strength respectively are 33.00MPa and 31.16MPa. Moreover, a significant increase of 13℃ in the onset decomposition temperature of degradation is observed, which suggests that the thermal stability of the composite prepared by S3M is also improved.
The curing behavior of a carbon fiber/epoxy prepreg under microwave radiation was investigated using differential scanning calorimetry(DSC) and Fourier transform infrared spectroscopy(FTIR), respectively. The carbon fiber/epoxy composite laminates were manufactured through microwave curing-vacuum bag molding process, and the existing overheating and broken issues of vacuum bags were studied. The results show that compared with thermal curing, microwave curing can significantly shorten curing time without altering molecular structure of the cured products. It seems that the size of the carbon fiber/epoxy prepreg influences its microwave curing characteristic. The problem of vacuum bag breakage, due to overheating in microwave curing of carbon fiber/epoxy composites, can be solved by controlling the microwave power, and the fabrication of the laminates with microwave radiation can be accomplished in about 60 minutes with more than 95% curing degree, indicating that microwave processing is shortened by more than half of curing time than conventional thermal curing(curing time more than 2h).
The chromized and laser quenching treatment were conducted on the surface of Cr12MoV cold worked die steel with salt bath method, the morphologies and phase components of the chromized layer were analyzed with SEM and XRD, respectively. The friction coefficient, wear properties and wear mechanism of the chromized layer were discussed. The results show that the thickness of the chromized layer is about 20μm, where Cr element exhibits gradient distribution to form the enrichment layer. The phases of chromized layer are composed of CrC3, CrC2,(Fe, Cr)2C3 and Cr with dense Cr2O3 film on the surface of chromized layer after chromizing and laser quenching treatment; the combination mode of chromized layer-substrate is metallurgical combination and mechanical combination, and metallurgical bonding ability is enhanced with chromizing and laser quenching. The friction and wear test is conducted using SiC ceramic ball as fiction pair, average friction coefficient of the chromized layer after laser quenching is 0.5795, decreases by 40.9% and 19.2% comparing with that of the original state and chromizing treatment respectively, reducing adhesion wear, the wear mode is abrasive wear, and the hardened layer and hard phase are main mechanisms of increasing wear performance.
Sodium ethaxide, one kind of nucleophiles, was added into bleached seedlac alcohol solution as dechlorination agent. It can react selectively with the carbon atom connected with chlorine, as a result the chlorine was removed by means of elimination reaction, and the products with low chlorine content was prepared. The effects of factors controlling the reaction on dechlorination efficiency were studied, such as dosage, temperature and time etc., and the structure of seedlac, shellac and low chlorine shellac were characterized by ultraviolet spectrometer. The results show that the conditions routed as dosage of 4.2g sodium ethanol per 100g bleached shellac, temperature as 90℃ and time as 90min are the optimal, and that the content of chlorine in the final products is 0.28% which is far smaller than 2.6% that of the products without dechlorination. Ultraviolet spectrometer analysis indicates the maximum adsorption wave of shellac is blue shifted to 222nm from 236nm, however it is recovered while the shellac is processed by dechlorination with sodium ethanol. As a result, the compacted chlorine of shellac can be eliminated by the process with the nucleophile, and the structure of shellac before and after elimination is different.
The AlxFeCrCoCuV(x=0, 0.5, 1.0) high-entropy alloys were fabricated by non-consumable vacuum arc melting furnace, the characteristics including microstructure, hardness and wear properties were examined by XRD, SEM, EDS and DSC. The results show that with the addition of aluminum, Al0.5CrFeCoCuV and Al1.0CrFeCoCuV alloys from single BCC phase of FeCrCoCuV to a transition duplex FCC/BCC phase;the hardness of Al1.0CrFeCoCuV alloy is larger than Al0.5CrFeCoCuV alloy. The alloys show adhesive wear behaviors, the wear-resisting performance of the alloys is proportional to its hardness. With the increase of friction time, the three alloys generate a layer of oxide on the surface and attach to the friction surfaces to improve the wear resistance.
Using a ball-on-flat contact mode, the torsional fretting wear of 5083 aluminum alloy flats against GCr15 steel ball were investigated under normal load(15, 50N) and torsional angular displacement amplitudes(from 0.1°to 10°).The results reveal that the T-θcurves change with the increasing of cycle numbers. It shows three types, i.e. the linear, elliptic and parallelogram loops.The torsional fretting running behaviors of 5083 aluminum alloy can be defined as three fretting regimes(i.e. partial slip regime(PSR), mixed fretting regime(MFR) and slip regime(SR)).The friction torque has a low value in the PSR but changes regularly in the MFR and SR. The wear scars observed by SEM reveal that the damage in the PSR is slight but serious damage wear is observed in the MFR and SR. The running condition fretting maps of 5083 aluminum alloy are set.
Aimed at the fiber crossover and undulation, a meso-scale model was proposed to analyze the residual stress in the undulation regions of filament-wound composites. The process induced residual stress fields of filament-wound composites during curing process was numerically simulated by commerce software. Based on transit heat conductive equation, curing kinetics model and composite laminated stress analysis theories, the corresponding formulas of the finite element analysis were introduced. The time's course and variation scope of residual stress during curing process were fully investigated through the example analysis. The results show that there is great difference of residual stress in different positions of fiber bundle. In laminated zone, the fiber bundle is under tensile stress state, while in fiber undulation zone, that is under compressive stress state, and the maximum residual stress appears in resin rich zone. The residual stress shows V-shaped trend along undulation direction, and it appears tensile or compressive stress state in different position of fiber bundle. The maximum compressive residual stress appears in the fiber maximize undulation angle.
The aging properties, absorption and mechanical properties of T700/5224 composites which were in hygrothermal environment and in 15# hydraulic oil, 4010# lubricating oil, RP-3 kerosene and AHC-1 cleaner were studied. The properties' changes and Tg of the T700/5224 composite were analyzed by infrared analysis(IR) and dynamic mechanical analysis(DMA). The results show that the absorption is 1.05% in environment of 80℃-85%RH, and 1.35% in environment of 80℃-100%RH. Shear strength is not changed obviously, but flexural strength decreases greatly. Open-hole tensile strength changes a lot, but on the whole, not decreases. Open-hole compression strength is always gradually decreasing. There is no evident impact on mechanical properties of composite by chemical solutions. The effect of AHC-1 cleaner on T700/5224 composite is bigger than the other three media, Tg declines 10℃ after soaking in AHC-1 cleaner for 45 days.
The stability of nano-scale oxides with the size less than 5nm in the helium atmosphere under irradiation in the ODS(oxide dispersion strengthened) materials was researched. The 14YWT alloy with pre-implanted with helium was irradiated at high temperature. Size, density, and composition of the nano-scale oxides were investigated by the atom probe tomography. The results show that nano-scale oxides are composed of oxides enrich in Ti and Y. The change of the size and composition of the nano-scale oxides under irradiation is trivial, indicating the good stability of nano-scale oxides in helium pre-implanted ODS materials under irradiation at 600℃.
The general situations of abradable coating in China and abroad were reviewed in this research, and the structure and application features of abradable coating in aeroengine were also introduced. The performance evaluation and technological researches of abradable coating were emphasized, too. The advantages and disadvantages of different abradable coatings and evaluation methods were compared. The application prospects and future research directions were put forward and clarified. The further focused research directions of both the abradable coating technological research and performance evaluations in China were declared, the study on coating preparation, structure of the coating, high temperature coating research and simulation technology need further development.
The present paper summarized abundant crucial results about the second phase particles(SPPs) for Zr-Sn-Nb-Fe zirconium alloy in the recent years, and systematically analyzed the influence of alloy elements(Sn, Nb, Fe, etc.) on the intrinsic characteristics(crystallographic structure, microchemistries, size, distribution, etc.) of SPPs. The precipitation and evolution mechanism of SPPs were analyzed during the processing and thermal treatment process. In addition, some measures to improve the type, size and distribution of SPPs were presented in the paper.
Solid state welding(SSW) has been increasingly applied in advanced metallic materials because of its outstanding advantages. Cold pressure welding(CPW), as a special SSW process, its interface bonding mechanisms and strength prediction are two difficult problems that have been puzzled the researchers for a long time. This paper reviewed the research status on the interface bonding mechanisms of CPW, emphatically discussed the influencing factors and prediction models of the interface bonding strength of CPW. It is pointed out that further research work on interface bonding mechanisms should overall consider the influences caused by diffusion, recrystallization and dislocation, while, building interface bonding strength models should overall consider the functions of deformation degree, deformation velocity and deformation temperature.
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