- 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)
High-strength aluminum alloys (2××× and 7×××, etc.) are widely used in aerospace, automobile and other fields because of their high specific strength and good machinability. With the development of high thrust-weight ratio engine and automobile lightweight technology, the demand for lightweight structural materials is increasing. Meanwhile, parts also present the "thin-walled, hollow and composite" tendency gradually, and the traditional processing methods of high-strength aluminum alloy are increasingly difficult to meet the requirements. As a common metal additive manufacturing (AM) technology, selective laser melting (SLM) is a great potential manufacturing technology for complex parts. SLM is expected to become an emerging technology to expand the application of high-strength aluminum alloys. However, due to their poor casting and welding properties, high-strength aluminum alloys easily produce the periodic hot cracks and coarse columnar grains during SLM, leading to unsatisfactory mechanical properties. Grain refinement is the key to overcome the inherent hot-tearing crack of SLMed high-strength aluminum alloys. The research progress in microstructure and mechanical property control of SLMed high-strength aluminum alloys in recent years was reviewed. The mechanical properties of alloys with different compositions were summarized. Importantly, the main strategies to suppress hot-crack formation in SLMed high-strength aluminum alloys were highlighted, including optimization of SLM process parameters and grain refinement by microalloying or addition of nanoparticles. It was pointed out that the main issue of SLMed high-strength aluminum alloys was the change of alloy composition on the comprehensive properties and heat treatment process was still unclear. The development trends were forecasted, such as designing new high-strength aluminum alloys and evaluating their comprehensive performances, using post-treatment process and other means to further improve the comprehensive performances of the alloys, and designing special grain refiners for SLM and investigating refinement mechanism.
Zr is one of the most deeply investigated and widely used microalloying elements. The low diffusivity of Zr and the formation of thermal-stable Al3Zr dispersoids with the properties of low density, high melting temperature and low interface misfit in Al matrix, making Zr owing a broad prospect of application in developing heat-resistant Al alloys. However, strengthening by Al3Zr has been limited by either low number density or low volume fraction. In addition, the interaction among multiple components is very complex in multi-component Al alloys during solidification, deformation and heat treatment, and it is very difficult to achieve a good combination in strengthening of Al3Zr with the intrinsic phase of each system. In this review, the existing form, the precipitation and coarsening behavior, and the strengthening mechanism of Zr element in Zr-containing Al alloys were summarized. The mechanism of complex microalloying with multiple elements on promoting Al3Zr dispersion was briefly introduced. Finally, the effects of Zr addition on several series of Al-based alloys were summarized. In sum, microalloying with Zr is of great significance for regulating microstructure and improving room temperature/high temperature strength in Al alloys.
Al-Zn-Mg series aluminum alloys have important applications in aerospace, transportation etc, for their excellent properties of low density and high strength. Further optimizing the microstructure to obtain higher mechanical properties and better corrosion resistance is the development direction of Al-Zn-Mg alloys. Microalloying has become an important means of improving the properties of aluminum alloys, owing to the limited space for alloy composition optimization and heat treatment processes improvement. The effects of microalloying elements on the mechanical properties, hot deformation behavior and corrosion resistance of Al-Zn-Mg alloys were briefly summarized, focusing on the different effects of the second phase particles formed by microalloying elements in different process stages, such as effectively refine grains and strongly hinder the movement of dislocations. The effects of pin grain boundaries, sub-grain boundaries and inhibiting recrystallization during hot deformation were discussed. The internal mechanism of improving the corrosion resistance of the alloy was explained. In addition, the further research direction of microalloying of Al-Zn-Mg aluminum alloy was prospected, understanding the interaction mechanism of microalloying elements and dual alloying-microalloying elements to realize the precise and accurate addition of microalloying elements will be one of the main research contents in the future. Clarifying the regulation effect of microalloying elements on deformation structures and dislocation configurations during hot working will provide a reference for improving the corrosion resistance of alloys.
The defects in friction stir welding (FSW) of aluminum alloy, e.g., tunnel defect, lack of penetration (LOP) and kissing bond, are with complex shape and narrow gap by inappropriate welding parameters. Firstly, the characteristics of FSW welding and typical defects were briefly described, and the difficult points in ultrasonic testing were summarized from the low time resolution, incomplete characterization of irregular defects, close acoustic impedance between kissing bond and Al alloy and the reduction of detection sensitivity. Subsequently, the research work on the ultrasonic testing for FSW of aluminum alloy were reviewed from the following four aspects, including conventional ultrasonic testing, time-of-flight diffraction (TOFD), phased array ultrasonic testing and other ultrasonic testing techniques. Finally, the research on the ultrasonic signal processing methods and machine learning methods was prospected. The signal characteristics were analyzed and extracted to further improve the resolution and signal-to-noise ratio of ultrasonic testing and realize the accurate identification and quantification for complex shape defects and subtle defects.
Precipitation temperature of Al3(Sc, Zr) dispersed phase in Al-Cu-Li-Sc-Zr alloys was investigated by DSC. Four kinds of triple-step homogenization treatments were designed to obtain the holding temperature and time of Al3(Sc, Zr) dispersed phase particles. After hot rolling, solution treatment and aging treatment, the mechanical properties of homogenized samples were compared by room temperature tensile tests. The apparent activation energy was calculated by the results of aging hardening curves, the morphology and composition of the second phase in homogenized samples were investigated by SEM and EDS, and the grain orientation characteristics of samples after solution treatments were investigated by EBSD. The results show that the Al3(Sc, Zr) dispersed phase at 460 ℃ which is the second step temperature in homogenizations is more favorable than that at 410 ℃ during the multistage homogenization treatments, which can control grain structure, inhibit recrystallization and promote the precipitation of strengthening phase containing Li during aging treatment. The compound action of grain boundary strengthening, texture composition and precipitated phase improves the mechanical properties of the alloys. In addition, for the dispersed particles like Al3(Sc, Zr) separated, many sub-grain microstructures are conserved after hot deformation annealing, which makes alloys deform uniformly during tensile process at room temperature and improves the ductility of the alloys.
Thermoplastic polyether ether ketone (PEEK) composites are widely used in aerospace field due to their excellent fracture toughness, impact resistance and material versatility. Sizing agent as the core auxiliary product of carbon fiber has an important impact on the interface of composites. Limited by the decomposition temperature, the traditional thermosetting sizing agents are difficult to meet the use of PEEK composites, which restricts the development and application of high-performance PEEK composites. Therefore, it is of great significance to develop a matching carbon fiber sizing agent for PEEK composites. In this paper, the interfacial properties of composites and the action mechanism of sizing agent were analyzed and introduced; the research progress and results of modified PEEK, polyimide precursor and polyetherimide sizing agents were focused, and different systems of sizing agents were analyzed and summarized.Finally, the relevant suggestions on carbon fiber sizing agents for PEEK composites were put forward while the environmental and multi-function developments for sizing agents were prospected.
As one of the most common transition metal oxides, manganese oxides have many advantages and show great potential in many fields. Its catalytic activity, adsorption capacity, stability, and other properties of manganese oxides can be adjusted by changing its crystal, morphology, pore structure and oxygen vacancies. To improve the MnOX activity performance, various preparation methods have been developed to adjust its crystal structure and morphology structure. In this work, the relationship between the structure of different crystalline manganese dioxides (α, β, γ, δ, λ) and their catalytic activity/adsorption performance activity was studied. The preparation methods on the morphologies structure (nanorods, nanosheets, nanoflowers, nanospheres) of MnOX materials were comprehensively summarized. Then, the typical application performance of manganese oxides materials in the energy file (catalytic conversion of biomass, electrochemistry) and environment (decomposition of gas pollutants, adsorption of heavy metals, degradation of organic pollutants) were summarized. Finally, the problems such as complicated action mechanism and poor stability of MnOX were analyzed.MnOX still has great application potential in the fields of environment and energy in the future.
In order to improve the crystallization properties of polylactic acid, the crystallization accelerator of graphene oxide grafted polyethylene glycol (GO-g-PEG) was prepared by esterification. The GO-g-PEG/poly(L-lactic acid) (PLLA) composite materials with different GO-g-PEG contents were prepared by solution blending method, and the structure was confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometer (XRD). The effect of GO-g-PEG on the crystallization behavior and thermal stability of PLLA was studied by differential scanning calorimeter (DSC), polarizing microscope (POM) and thermogravimetric analyzer (TGA). The results show that under the heterogeneous nucleation and plasticization of GO-g-PEG, the crystallization nucleation density of GO-g-PEG/PLLA composites is increased significantly, the crystallization ability and crystallinity are improved; when the grafting amount of PEG is 11.8%(mass fraction), comparing the thermal stability of GO-g-PEG/PLLA composites with PLLA neat, the thermal decomposition temperature of GO-g-PEG/PLLA composites is increased by about 20 ℃.
Multilayer graphene(MLG) and MLG/Fe2O3composite nanomaterials were prepared by liquid-phase stripping. The prepared MLG, MLG/Fe2O3composite nanomaterials and MLG+Fe2O3mechanically mixed nanomaterials were directly added onto the titanium alloy/steel sliding interface. Subsequently, the dry sliding friction and wear tests were performed, and the friction and wear behavior of TC11 alloys was measured. The X-ray diffractometer, laser Raman spectrometer, scanning electron microscopy, 3D laser scanning microscopy and energy spectrometer were employed to analyze the structure, morphology and component of the worn surface and subsurface for TC11 alloys. The results show that, as for the single additive of MLG, the variation tendency of wear loss and friction coefficient for TC11 alloy is similar to that without any additives. There is only Ti and no other phases on the worn surface. The characteristics of adhesive wear and abrasive wear are presented, which are manifested as plastic tearing, adhesive traces and furrows. Underneath the tribo-layer, there exist a plastic layer, which means that TC11 alloy substrate suffers a plastic deformation during sliding. When MLG/Fe2O3composite nanomaterials and MLG+Fe2O3mechanically mixed nanomaterials are selected as the additives, the wear loss and friction coefficient invariably maintain extremely low values and close to zero, in a certain range of sliding revolutions. There retain the phases of MLG and Fe2O3 on the worn surface. The typical black regions and grey regions are observed, and the tribo-layers are presented a double-layer structure. With an increase of cycles to 25000, the double-layer tribo-layer form with the addition of composite nanomaterials disappear, and the severe wear appears. However, as for the addition of mechanically mixed nanomaterials, the double-layer tribo-layer steadily exists. Therefore, the single addition of MLG is unable to improve the friction and wear properties of titanium alloy. With an addition of MLG to the Fe2O3-contained tribo-layer, a new tribo-layer, i.e. double-layer tribo-layer is formed. This layer simultaneously possesses lubrication and bearing function, resulting in a significant improvement for the friction reduction and wear resistance of titanium alloys. Especially, the titanium alloys present more excellent tribological properties with the addition of mechanically mixed nanomaterials, because of more layers and higher content of MLG in the double-layer tribo-layer.
Shape-stabilized SiO2 aerogel phase change composites (PCCs) was prepared by physical adsorption method with SiO2 aerogel as support material, and then used for secondary packaging.The optimal adsorption ratio of SiO2aerogel and phase change materials was explored, and microscopic morphology, chemical composition, pore structure, phase change characteristics, thermal reliability, shape stability and thermal insulation performance of composites were also characterized. The results show that the PCCs with 80%(mass fraction) phase change material (LS-80) has the optimization proportion, the composites exhibit shape-stability during the phase change process, and the melting point and melting enthalpy are -15.6 ℃ and 170.2 J/g respectively. The successful adsorption of SiO2 aerogel makes the specific surface area, pore size and pore volume of LS-80 reduced to 59 m2/g, 13 nm and 0.2 cm3/g. After 20 thermal cycles, the latent heat of packaged phase change material is decreased by 13.4%, while the SL-80 is only decreased by 2.8%, which proves good thermal reliability. Besides, the thermal conductivity of the composites is reduced and the thermal insulation capacity is enhanced due to the addition of SiO2 aerogel. The results provide experimental basis for the application of SiO2 aerogel PCCs in the field of cold chain logistics.
The traditional preparation process of superhydrophobic surfaces(SHS) is complicated and the mechanical stability of SHS is less than satisfactory in most cases, which seriously restricts the practical application. The "binder+nanoparticles" strategy was used to prepare a nonfluorinated, durable and stable superhydrophobic epoxy composite coating on magnesium alloy. The contact angle test results show that the maximum contact angle of the composite coating is 160.2°, and the contact angle is still as high as 103° even after 30 days of soaking in 3.5%(mass fraction) NaCl solution; EIS results indicate that the |Z|0.01 Hz of the composite coating is still above 109 Ω·cm2 even after five accelerated aging cycles, demonstrating excellent resistance to salt fog and anticorrosion performance; Friction and wear test results reveal that the |Z|0.01 Hz of the composite coating is as high as 1.84×109 Ω·cm2 after mechanical friction under 19.6 N load for 8 h. Due to the excellent blocking barrier of "air cushion", the composite coating can provide efficient and durable corrosion protection for magnesium alloy and the "adhesive+nanoparticles" strategy provides a new direction for the preparation of superhydrophobic coating.
Both deformation temperature and strain rate affect the mechanical properties of β titanium alloy, and are related to the change of deformation mode in the process of plastic deformation. The effects of deformation temperature and strain rate coupling on the mechanical properties of {332}〈113〉 twinning induced plastic effect Ti-15Mo alloy were studied by TEM, EBSD, SEM, XRD, OM and tensile testing machine.The results show that as increase of strain rate, yield strength increases at 298 K and 573 K, which is intensively dependent on dislocation thermal activation behavior. The larger contribution of dislocation activation at 573 K exhibites the higher strain rate dependency on yield strength. At 573 K, the Ti-15Mo alloy is deformed by {332}〈113〉 twinning and dislocation slip, which is different from that at 298 K, and the established flow stress model indicates that dislocation strengthening has a greater contribution. At a high strain rate, the formation of more twins at early deformation suppresses the subsequent formation of twins, decreasing the work hardening rate, whereas can effectively decrease the local stress concentration due to the inhomogeneous distribution of dislocations, delaying the necking. Consequently, these two factors result in the lower strain rate dependency on flow stress in the Ti-15Mo alloy under the coupling effect of deformation temperature and strain rate.
A spinel type of urchin-like MgCo2O4 electrode material was obtained by facile hydrothermal method. The products were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and electrochemical performance of the products was tested by electrochemical workstation measurements. By changing the hydrothermal reaction time, cluster structure, uniform distribution, together with high density of urchin-like MgCo2O4 material can be synthesized. The results show that as the hydrothermal reaction time reaches 6 h, the structure of MgCo2O4 electrode material is relatively perfect, its size is more uniform, and the electrochemical performance is better. Furthermore, at a current density of 1 mA/cm2, area specific capacitance reaches up to 6.75 F/cm2. Additionally, the specific capacitance is maintained at 88.4% after 1000 cycles at the current density of 20 mA/cm2, showing good cycle performance.
Direct-current ZnO varistor ceramic samples were prepared by traditional ceramic sintering process with B2O3, In2O3 and Al2O3multi-donor doping. The effects of B2O3 doping ratio (0.1%-0.4%, molar fraction) on the microstructure and electrical properties of direct-current ZnO varistor ceramics were investigated. The phase, morphology, composition and electrical properties of the samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and digital source meter. The results show that the co-doping of multi-donor dopants (Al2O3, In2O3 and B2O3) can significantly improve the comprehensive properties of direct-current ZnO varistor ceramics. Al3+ improves the conductivity of the samples and reduces the residual voltage ratio of the samples; In3+ restricts the growth of grains through pinning effect and improves the voltage gradient of the samples; the doping of B3+ improves the surface state density of the sample, increases the barrier height and effectively suppresses the increase in leakage current. When the doping amount of B2O3 is 0.3%, the comprehensive performance of the sample is the best: the voltage gradient is 486 V/mm, the leakage current density is 0.58 μA/cm2, the nonlinear coefficient is 85, and the residual voltage ratio is 1.55.
Polyether imide (PEI) flat ultrafiltration membrane was prepared by immersion precipitation phase inversion method. The effects of polymer PEI concentration and additive polyvinylpyrrolidone (PVP) concentration on the structure and properties of membrane were investigated. In order to improve the solvent resistance of ultrafiltration membrane, hexamethylenediamine (HDA) was used for chemical crosslinking, and the difference of membrane performance under different crosslinking time was studied. The results show that the flux of the crosslinked membrane is effectively improved without reducing the membrane separation performance compared with the uncrosslinked ultrafiltration membrane. Under the operating pressure of 0.1 MPa, the flux of pure water is increased from 667.1 L/(m2·h) to 1126.1 L/(m2·h), while the rejection rate of 1.0 g/L BSA solution remains above 97%. After soaking in six different solvents for 48 h, it was found that the uncrosslinked membrane is completely dissolved in N, N-dimethylformamide (DMF), while the crosslinked membrane still maintains a good membrane morphology with an adsorption capacity of 0.86 g/g. The adsorption capacity in ethanol, isopropanol, n-hexane and 1 mol/L HCl solution is smaller than that of the uncrosslinked membrane, but is increased in 1 mol/L NaOH solution, which indicates that the prepared crosslinked membrane has good solvent resistance and strong acid resistance, but the strong alkali resistance becomes worse.
The effect of the substrate surface roughness on tribological properties of MoS2/Ti films, and the friction and wear mechanism was studied. MoS2/Ti films were deposited on bearing steel with different surface roughness by magnetron sputtering. The adhesion strength between the film and substrate, phase composition, surface morphology and surface roughness of MoS2/Ti films were obtained respectively by scratch tester, X-ray diffractometer(XRD), scanning electron microscope (SEM) and roughness profiler. And the tribological properties of MoS2/Ti films under dry friction, solid-oil composite lubrication and solid-grease composite lubrication were studied by a ball-on-disk tribometer. The results show that with the increase of the substrate surface roughness, the surface roughness of MoS2/Ti films increases, the intensity of (002)MoS2 and (100)MoS2 diffraction peaks first decreases and then increases, and the adhesion strength between the film and substrate decreases. When the surface roughness of the substrate is 0.01 μm, the MoS2/Ti films have good lubrication characteristics under dry friction condition. The average friction coefficient is 0.101, and the wear scar is shallow and small. With the increase of substrate roughness, the average friction coefficient and the wear rate of the samples increase first and then decrease. Meanwhile, the main wear mechanism of the film changes from abrasive wear to chip formation and fragmentation. And the effect of intermolecular interaction is greater than that of mechanical engagement, when the substrate roughness of the samples is large (Ra=0.26 μm). Under the condition of solid-oil composite lubrication, there is no fragmentation phenomenon on the worn surface with large substrate roughness. The wear scar is shallow, and the average friction coefficient is reduced by about 19%. Under the condition of solid-grease composite lubrication, the tribological properties of the samples are poor, and the effect of the substrate surface roughness on the friction coefficient is not significant.
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