- 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)
Graphene oxide/copper (GO/Cu) composites were successfully synthesized through the ball milling and vacuum hot press sintering process. The morphologies of the mixture powders, and the microstructure and mechanical properties of GO/Cu composites were investigated by OM, SEM, XRD, hardness tester and electronic universal testing machine, respectively. The results show that the GO/Cu composites are compact. Graphene oxide with flake morphology is uniformly dispersed and well consolidated with copper matrix. When the mass fraction of graphene oxide is 0.5%, the microhardness and compress strength at RT reach up to 63HV and 276 MPa, increased by 8.6% and 28%, respectively. The strengthening mechanism is load transfer effect, dislocation strengthening and fine crystal reinforcing.
Optical microscopy(OM), scanning electron microscopy(SEM), EDX and EIS combined with ultramicrotomy were employed to investigate the micro morphology, chemical composition and electrochemical properties of anodized 2A97 Al-Cu-Li alloy before and after atmospheric corrosion. The results show that when electrolytes containing combinations of tartaric-sulfuric or boric-sulfuric acid are used to grow the films at different temperatures, boric acid addition and higher temperature allow for higher current density that speeds up the film growth. The pore geometry and structure is similar for different electrolytes. Dispersive dark rusty spots composed of O, Al, Cl, Cu are present on the boric-sulfuric acid anodized specimen after exposure in tropical marine atmosphere for 1 month. Deposition of white corrosion product is found on the specimen surface as well. Severe pitting occurs and develops deeply into the alloy substrate after elongated outdoor exposure. Corrosion propagation is associated with θ-phase particles.
The thermal compression experiment of GH984G18 alloy was carried out using thermal-mechanical testing machines Gleeble3800. Based on the stress-strain curves obtained from the experiments, the processing maps of the GH984G18 alloy were established according to the dynamic materials model (DMM), then the hot working process window of alloy was built, and the influence of temperature and strain on the dynamic recrystallization of the experimental alloy was also analyzed. The results show that when the strain is small(ε≤0.2), the optimum deformation temperature is in the temperature range of 1030-1090℃ and strain rate range of 0.01-0.18s-1; with the increase of strain(ε≥0.3), the optimum deformation temperature moves to the high temperature range of 1180-1200℃ and strain rate range of 0.056-0.25s-1; and at the strain rate of 1s-1, dynamic recrystallization does not occur and dynamic recovery dominates when the temperature is lower than 900℃; and partial dynamic recrystallization occurs at the temperature of 1000℃ and the strain of 30%; and then the complete dynamic recrystallization occurs at the temperature of 1000℃ and strain of 60%.
A novel light-mass high Mn-Al austenitic wear-resistant steel was selected as the research object. The microstructure and precipitates were examined by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). Effect of heat treatments on microstructure and mechanical properties of the novel steel was studied. Results show that the optimum heat treatment is water toughening at 1050℃ for 1h and aging at 550℃ for 2h, air cooling. Under the condition of the optimum heat treatment, fine (Fe, Mn)3AlC carbides which have a perovskite structure are found to precipitate within the austenite matrix. The fine carbides not only strengthen the austenitic matrix, but its mechanical properties are also improved significantly. The hardness, strength, impact toughness of the experiment steel under the optimal heat treatment reach the best match with a tensile strength of 825MPa, a yield strength of 574MPa, a impact toughness values (V-notch) of 156 J/cm2, a surface hardness of 271HB. Compared with that of the conventional treatment, the yield strength and hardness increase by 40.0% and 32.2%, respectively.
Al-Si-Cu-Zn filler metal was developed to braze 3003 aluminum alloy. The microstructure and fracture surface of the joint were analyzed by XRD, SEM and EDS, and the effects of brazing temperature on microstructure and property of the joint were investigated. The results show that good joints are obtained at brazing temperature of 540-580℃ for 10 min. The brazed joint consists of α(Al) solid solution, θ(Al2Cu) intermetallic compound, fine silicon phase and AlCuFeMn+Si phase in the central zone of brazed seam, and α(Al) solid solution and element diffusion layers at both the sides of brazed seam, and the base metal. The room temperature (RT) shear fracture of the joint occurs at the interface between the teeth shape α(Al) in the diffusion layer and the center zone of brazed seam, which is mainly characterized as brittle cleavage. As the brazing temperature increases, α(Al) solid solution crystals in the diffusion zone grow up, and the interfacial bonding of the joint is in the form of interdigitation. Brazing at 560℃ for 10 min, the RT shear strength of the joint reaches the maximum value of 92.3MPa, which is about 62.7% of the base material.
Primary recrystallization annealing was operated in 3%(mass fraction)Si CGO steels. Different annealing holding time was set up in experiments. Microstructure, dislocations and texture distribution were analysed by OM, TEM and EBSD techniques. Evolution of microstructure and texture in primary recrystallization was studied. Results indicate that as the annealing holding time prolongs, recovery and recrystallization occur gradually. When the holding time increases to 300s, recrystallization is almost fully realized and grains are equiaxed. With the extension of holding time, the dislocation density decreases. Primary recrystallization texture is affected by holding time. As the holding time extends, {111} < 112> texture and {110} < 112> texture are weakened and Goss texture is strengthened. {111} < 110> texture is reduced firstly and then increases. The intensity of cube texture and rotated cube texture is stable. When holding time is short, grains are dominated by small angle grain boundaries with the existence of a large amount of subgrains. As the holding time prolongs, large angle grain boundaries increase.
The curing kinetics of high temperature resistance bismaleimide resin was studied by dynamic DSC analysis, and the parameters of the curing reaction were obtained to establish a phenomenological model based on Kissinger and Crane equations. The relationship between glass transition temperature and curing degree was analyzed with isothermal DSC method based on DiBenedetto equation. Moreover, the relationship between gel-time and temperature was investigated by gelation disk. Finally, the time-temperature-transition (TTT) diagram was built to guide the process of the resin. Results show that appropriate pressure timing can be determined according to the TTT diagram. Thus, air in or between layers of prepreg can be eliminated effectively to prepare composites with good internal quality.
PAN-based carbon fibers were modified by electrochemical oxidization using fatty alcohol polyoxyethylene ether phosphate (O3P), triethanolamine (TEOA) and fatty alcohol polyoxyethylene ether ammonium phosphate (O3PNH4) as organic electrolyte respectively. Titration analysis, single fiber fracture strength measurement and field emission scanning electron microscopy (FE-SEM) were used to evaluate the content of acidic functional group on the surface, mechanical properties and surface morphology of carbon fiber. The optimum process of electrochemical treatment obtained is at 50℃ for 2min and O3PNH4 (5%, mass fraction) as the electrolyte with current density of 2A/g. In addition, the surface properties of modified carbon fibers were characterized by X-ray photoelectron spectroscopy (XPS) and single fiber contact angle test. The results show that the hydrophilic acidic functional groups on the surface of carbon fiber which can enhance the surface energy are increased by the electrochemical oxidation using O3PNH4 as electrolyte, almost without any weakening to the mechanical properties of carbon fiber.
Unstressed exposure tests of Inconel 740H alloy tube were carried out at 750℃ for 500-3000h. The microstructure evolution and microhardness were studied by means of thermodynamic simulation, OM, FEG-SEM and microhardness testing. The results show that the tube is qualified if both chemical composition and tensile properties of the as-received alloy meet the corresponding requirements of ASME. After long term exposure, the main precipitates are γ' and M23C6, and no η and σ phase. With the prolonging of exposure time, the coarsening of γ' becomes faster and the law of relationship between the radius of γ' and time accords with LSW Ostwald ripening law; meanwhile, the change in size of M23C6 is not so obvious. During the whole process, microhardness increases firstly and then decreases, but the fluctuation is slight. The changes of microstructure and hardness indicate that, after long time exposure, the domestic Inconel 740H has good stability and can be used for further carrying out the investigation on the mechanical property of creep-rupture.
Cu2ZnSnS4 (CZTS) thin films were prepared by solid-state sulfurizing Cu-Zn-Sn(CZT) metallic precursors. The effect of sulfurization time on phases, chemical composition, surface morphology and optical properties was investigated by X-ray diffraction (XRD), Raman spectrum, energy dispersive of X-ray (EDS), scanning electron microscope (SEM) and UV-Vis, respectively. The results show that with the sulfurization time and content of Cu increase, Zn particularly decreases. The films that sulfurized over 40min occur with impurities like SnS, Sn2S3 and Cu2SnS3, which lead smaller optical band gap. When the sulfurization time is 20min, the sample is single phase CZTS thin film, which surface is uniform and even, Cu-poor and Sn-rich. The absorption coefficient is over 104cm-1. The band gap energy is estimated 1.56eV.
The effects of Mg and Ag contents on the corrosion resistance of Al-Cu-Mg-Ag alloy were investigated by intergranular corrosion (IGC) testing. The corrosion mechanism of the alloys with different chemical composition was discussed by transmission electron microscopy (TEM) and electrochemical analyses. The results indicate with increasing Mg and Ag content, the age hardening rate of the alloy increases. The size of the strengthening phases Ω decreases with increasing Mg content whereas phase volume fraction increases. More solution atoms are consumed to form the precipitation on the grain boundaries of the alloy with higher Mg content, which increases the potential difference between precipitation free zone (PFZ) and the matrix and subsequently, the IGC resistance of Al-Cu-Mg-Ag alloy decreases. Increasing the Ag content, the main strengthening phases transform from great amounts of θ' with less Ω to plentiful Ω with less θ'. The variation of Ag content hardly affects the potential of PFZ, and the corrosion resistance of the alloy depends mainly on the width of PFZ. With increasing Ag content, the precipitations on the grain boundaries are refined; the width of PFZ decreases and correspondingly, the corrosion passageway becomes narrow. The IGC resistance of Al-Cu-Mg-Ag alloy is enhanced with increasing Ag content.
Effect of intermediate annealing on the microstructure and properties of 5182 aluminum alloy sheet with full annealed state (5182-O) was investigated by means of optical microscope, scanning electron microscope and universal testing machine. The results indicate that compared with 5182-O sheet without intermediate annealing, 5182-O sheet with intermediate annealing possesses too fine grain size, intermetallic compounds not broken enough, larger size intermetallic particles, less dispersed phase. Yield strength and ultimate tensile strength, work hardening exponent and normal anisotropy of plastic strain ratio decrease but planner anisotropy of plastic strain ratio increases. The mechanical properties and forming ability of 5182-O aluminum alloy sheet and its microstructure are not improved significantly after intermediate annealing.
The Mg-4.4Zn-0.3Zr-0.4Y (mass fraction/%) alloy ingots were prepared by two casting processes namely air cooling and water cooling. These two types of Mg-4.4Zn-0.3Zr-0.4Y alloy ingots were extruded and then ageing treated under the same conditions, and the effect of ageing treatment on the microstructure and mechanical properties of the alloys was studied. The results show that the lamellar eutectic structure and dendrite cell size are significantly refined under water cooling, which restrain the formation of W phase (Mg3Y2Zn3) and promote the increase of volume fraction of I phase (Mg3YZn6) in the as-cast alloy. For the different original microstructure and second phase, the ultimate tensile strengths of the extruded Mg-4.4Zn-0.3Zr-0.4Y alloy under water cooling and air cooling reach 327MPa and 306MPa respectively, and the elongations of the alloy reach 14.8% and 10.0% respectively. After ageing treatment, the grain size and texture intensity change slightly. Thus, the contents of precipitated phases (MgZn and MgZn2) mainly affect the mechanical properties of the extruded alloy. The aged as-extruded alloy exhibits a tensile yield strength, an ultimate tensile strength and an elongation of 330, 348MPa and 14.4% respectively under water cooling, and 344, 359MPa and 8.6% respectively under air cooling.
The stress relaxation behavior and springback equation of 7050 aluminum alloys during the age-forming process were studied through self-designed uniaxial tension device. The results show that in traditional aging temperature, the stress relaxation curve of 7050 aluminum alloys exhibits a classical logarithmic decrement curve. The stress relaxation process can be divided into three stages, which are the initial stress decayed fast stage, the subsequent stress slowly decayed stage and the stress constantly maintained stage, respectively. Stress relaxation limit of 7050 aluminum alloys decreases with increasing aging temperature. The threshold stress presents during the stress relaxation process due to the interaction between precipitation behavior and dislocation creep of 7050 aluminum alloys. The stress relaxation equation of 7050 aluminum alloys is obtained through resolving the feature and Taylor equation of relaxation process, and using the stress relaxation equation can precisely predict the springback of workpiece after age-forming.
The stuffed shield with multi-layer insulation(MLI) was designed by improving on Al Whipple shield, and a series of high-velocity impact tests were practiced with a two-stage light gas gun facility at vacuum environment. The damage model of the stuffed shield with different MLI location by Al-sphere projectile impacting was obtained. The effect of MLI on damage of the stuffed shield by high-velocity impact was studied. The results indicate when the MLI is located at front side of the first Al-plate, the protection performance of the stuffed shield is improved with the larger perforation diameter of the first Al-plate and more impact kinetic energy dissipation of the projectile. When MLI is arranged at back side of the first Al-plate, the expansion of the secondary debris cloud from projectile impacting the first Al-plate is restrained, it is not good to improve the protection performance of the stuffed shield. When MLI is arranged at front side of the stuffed wall, the perforation size of the stuffed wall increases; when MLI is arranged at front side of the rear wall, the distribution range of crater on the rear wall decreases.
Fatigue life evaluation of retired parts is always one of the most difficult problems in remanufacturing engineering. Tension-tension fatigue experiments of precut groove sucker rod specimens were conducted, and on-line magnetic memory signals on the surfaces of specimens under different cyclic numbers were measured by magnetic memory testing instrument, and the variation regularities of the tangential amplitude and normal peak-peak value with different fatigue damage were exploited simultaneously. The Lissajous figure introduced shows that the surrounded area becomes larger, the largest and smaller finally, whilst the maximum closure area corresponds to the critical state of macroscopic crack about to unstable propagation. Furthermore, the maximum value of synthetic magnetic field gradient is proposed as an index to predict fatigue life. The results demonstrate that the characteristic parameter can reflect different development stages of fatigue cycles, and the quantitative relationship between the characteristic parameter and the normalized life is established by virtue of Gauss function, which can be used to predict the fatigue life of sucker rods.
An amphiphilic random copolymer of polyglycidyl methacrylate-co-N-vinyl carbazole P(GMA-co-NVC) was synthesized by free radical polymerization and was used to noncovalently modify multi-walled carbon nanotubes (MWCNTs). The obtained P(GMA-co-NVC)/MWCNTs was mixed with epoxy resin and used to reinforce epoxy resin. Polymer modified carbon nanotubes/epoxy resin composites were prepared by a casting molding method. Tensile test, electrical resistivity test and differential scanning calorimeter(DSC) analysis were used to study the effect of polymer modified carbon nanotubes on the mechanical, electrical, and thermal properties of epoxy resin. The results show that the epoxy composite reinforced with P(GMA-co-NVC)/MWCNTs shows a remarkable enhancement in both tensile strength and elongation at break compared to either the pure epoxy or the pristine MWCNTs/epoxy composites. In addition, the electrical conductivity of epoxy is significantly improved and the volume resistivity decreases from 1014Ω·m to 106Ω·m with 0.25% mass fraction loading of P(GMA-co-NVC)/MWCNTs. Moreover, glass transition temperature of the epoxy composite also increases from 144℃ to 149℃.
Amorphous Ni-P alloy coatings were prepared on 45 carbon steel blocks using electrodeposition method. The thermal effect and quality change of Ni-P alloy coating under heating rate of 20℃/min were analyzed by differential scanning calorimetry (DSC) and thermogravimetry (TG). Coatings were heat-treated at 300℃ and 400℃ for 0, 15, 30, 45, 60, 75min respectively, coating surface was characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), microhardness tester. The result shows that the exothermic peak of Ni-P alloy coating appears at 284.8℃, coating quality and elemental composition are stable during the heat treatment. Crystallization process experiences a transformation of amorphous, metastable state NiP and Ni5P2, stable state Ni3P. The microhardness of coating can be improved remarkably after heat treatment, namely, the maximum value of heat-treated coating is 1036.56HV, which is nearly 2 times as hard as as-deposited coating. The corrosion resistance of heat-treated Ni-P alloy coating in NaCl solution is inferior to as-deposited coating, but they are both much better than 45 carbon steel substrate.
Properties, research progress and application status of polyimide composite bushings for aeroengine were reviewed. The manufacture technology, performance and applications of graphite filled composite bushings, braid composite bushings and chopped fiber composite bushings were primarily introduced. It is pointed out that low cost, continuous manufacture process, high heat resistance and long-service life will be the main directions of polyimide composite bushings for aeroengine and its materials system in the future.
|
Founded in 1956 (monthly) ISSN 1001-4381 CN 11-1800/TB Sponsored by AECC Beijing Institute of Aeronautical Materials |
