- 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 refractory high-entropy alloys (RHEAs) usually form a multi-principal elements alloy with equal atomic ratio or near equal atomic ratio via adding a variety of high melting point elements, showing simple phase composition and excellent high temperature properties, and processing a broad application prospect in the field of superalloy. Based on the performance characteristics and preparation process of RHEAs, and from the perspective of the current situation and challenges in fabrication and forming, the property tuning methods and its research progress of RHEAs were summarized, as well as the achieved breakthrough and the facing dilemma of the additive manufactured RHEAs. A prospection on the composition design and optimization, material preparation and processing, and additive manufactured forming of RHEAs was also proposed.The following suggestions are put forward for the key research trend of RHEAs in the future: tuning phase composition and phases interface to overcome the strength-ductility trade-off of RHEAs, designing alloys by combining the mature traditional strengthening and toughening theory with the properties of RHEAs, modifying the formability and properties of RHEAs by drawing support from the processing characteristics of additive manufacturing technology, and investigating the servicing performance and failure mechanism in high temperature or multi-field coupling condition of RHEAs.
High chemical activity and unique electrochemical behaviour are responsible for the complicated corrosion mechanism of magnesium. Importantly, the anodic hydrogen evolution on Mg electrodes when applied anodic polarization is one of the greatest important characteristics for Mg corrosion. The phenomenon, referred to as negative difference effect (NDE), has always been of an interest in terms of Mg electrochemistry corrosion. In this article, the research progress of hypotheses and theories proposed to interpret this phenomenon was reviewed: assuming that univalent Mg+ existed during anodic polarization of Mg. According to this, increasing oxidation rate of magnesium by applying an anodic polarization increased the rate of hydrogen evolution since the rate of Mg+ entering into electrolyte increased at the same time. However, this theory has raised criticism since Mg+ has never been experimentally detected, despite the requirement of its finite lifetime. Film theory declared that the dark corrosion products containing bilayer of MgO and Mg(OH)2 films form on the corroded surface of magnesium were believed to exhibit enhanced catalytic activity towards hydrogen evolution as well. In addition, this declaration has been proved experimentally: hydrogen evolution rate on the dark corroded regions was faster than that on the uncorroded regions at free corrosion, especially at the boundaries of the corroded/uncorroded regions. However, the latest experiments demonstrated that the increase in cathodic activity of the corroded regions during anodic polarization provided a minor contribution to the increase in hydrogen evolution rate during anodic polarization, and rather the enhanced hydrogen evolution at anodic potentials (NDE) was dominated by the regions where the net anodic reaction occurred. Assuming that enrichment of impurities such as Fe and Mg atoms took place in corrosion products of Mg. It is believed that Fe enrichment was capable of enhancing catalytic activity towards hydrogen evolution. There were indeed evidences (microscope images) showing the enrichment of Fe atoms around the interface of metal/solution. Unfortunately, the accumulation of these atoms on the electrode only contributed to a very small part to hydrogen evolution in NDE in further studies. Further, some researchers asserted the great possibility of the existence of MgH2 which had a similar mechanism of NDE to univalent Mg+. Still, the experimental existence and stability of such intermediate agents were of great concern. Another study proposed a theory that H2O molecules were always of absorption and desorption on Mg electrode, which provided sufficient H atoms for NDE to take place. Though all these assumptions contributed to explaining the NDE phenomenon to some extent, they were still not so reasonable to be generally accepted. At last, it was pointed that the future development direction of the NDE phenomenon by using advanced in-situ electrochemistry techniques and adjusting the electrochemical parameters, to expect a reasonable NDE mechanism, further to develop the corrosion theory of metals.
TiO2 nano-film type gas sensor has the advantages of simple preparation method, high sensitivity, good consistency and miniaturization, and the wide band of TiO2 semiconductor enables it to greatly improve the performance of the sensor by coating other elements. Nowadays, it has received more and more attention from researchers. In this paper, the research progress of TiO2 gas sensor at home and abroad was reviewed. The application of TiO2 thin film gas sensor in the detection of six common reducing gases(H2, NH3, H2S, VOC, CO, SO2) and two common oxidizing gases(CO2 and NOx) was introduced. In the application of gas detection, the sensing performance and sensing mechanism were discussed and the future research and development of TiO2 thin film gas sensor were prospected such as doping conductive particles, precious metals or metal oxides into TiO2 to improve its performance, which provides a reference for the study of new gas sensor.
Ion-imprinting technology endows with the selective separation for target ions, which has the advantages of high predeterminability, recognition, stability and practicality. The ion-imprinted materials obtained by the ion imprinting technology have the characteristics of simple process, easy operation, good stability and high selectivity. In order to meet the needs of lithium resources, ion-imprinted materials have been used for the development and utilization of lithium resources in water samples with complex compositions. In this article, the characteristics of ion-imprinted materials and their preparation principles were briefly introduced, and the main components of Li+-imprinted material preparation systems were summarized. Furthermore, the research progress of Li+-imprinted materials was reviewed with emphasis on the current research status of advanced Li+-imprinted materials. At present, advanced Li+-imprinted materials are mainly prepared by surface ion imprinting polymerization combining with new technologies, such as adsorption columns, magnetic separation, and membrane separation, to enhance selective recognition for lithium and simplify separation and recovery operations. Finally, the problems in the preparation and application of Li+-imprinted materials are proposed, and their future development and application prospects were prospected.
Polymer matrix composites (PMCs) have become one of the most important structure materials in the new generation of civil turbofan aeroengine due to their advantages of high specific strength, high specific stiffness, good designability, excellent vibration damping performance and feasible integrity fabrication. The PMCs application in aeroengine abroad based on fan blade, fan casing, acoustic liner and bushing was introduced firstly in this paper. The advantages of PMCs in structure optimization, economy and environmental friendliness were also illustrated. Moreover, new progress of PMCs including micro/nano material hybridization, 3D printing process and metamaterials in aeroengine was analyzed in details. Finally, some suggestions about PMCs application based on the relationship of "design-material-process-evaluation" were proposed for further development of civil turbofan aero engine in China.
The non-isothermal reaction kinetics of cyanate ester system was investigated by dynamic differential scanning calorimetry (DSC). The analysis of non-isothermal data was carried out by using the model-fitting Kissinger, Flynn-Wall-Ozawa, and Crane methods. The results indicate that the apparent activation energy of the curing reaction is 101.3 kJ·mol-1 and 99.4 kJ·mol-1calculated from Kissinger and Flynn-Wall-Ozawa models, respectively. The reaction sequence of the adhesive is 0.92 calculated from Crane model. In addition, the relationship of the curing degree with the curing temperature and the curing time is established. The curing parameters are obtained by adopting "T-β" and "t-β" extrapolation, and the strength test proves the validity of the curing parameters designed in this paper. These results constitute a theoretical basis for the curing and application of the cyanate ester adhesives.
The carbon fiber/epoxy resin composites with different stitch density were manufactured using modified lock stitching and vacuum assisted resin infusion (VARI) molding process. The influence of stitch space and stitch pitch on mechanical properties of the composites was investigated. The optimum stitch density was obtained. The results show that with increasing stitch space, both tensile and flexural properties enhance and interlaminar shear strength increases first and then decreases. With the increase of stitch pitch, both tensile and flexural properties exhibit an increasing trend. The stitched composites have the optimum integrated mechanical properties when the stitch density is 5 mm×8 mm. Their tensile strength, tensile modulus, flexural strength and flexural modulus reduce by 13.3%, 12.7%, 23.0% and 25.2%, respectively, whereas the interlaminar shear strength increases by 11.3% compared to the unstitched composites.
The morphologies and surface chemical properties of domestic T800 grade carbon fibers A and imported Toray T800H were characterized by means of scanning electronic microscopy(SEM), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The mechanical properties of two kinds of carbon fiber reinforced high toughness epoxy resin matrix composites were studied.The results show that the surface properties of carbon fiber have a significant effect on the interface properties of the composite. The surface roughness and surface chemical activity of domestic carbon fiber A are close to those of Toray T800H carbon fiber, and the interfacial properties of the two kinds of carbon fiber composites are basically the same at room temperature, which indicates that domestic carbon fiber composite M-A has good interfacial properties. Under the condition of 130 ℃ and wet state, both the retention rate of interlaminar shear strength and 90° tensile strength of domestic carbon fiber composite M-A are slightly higher than that of Toray carbon fiber composite M-T800H, which indicates that the domestic carbon fiber composite M-A has good hydrothermal property.
Graphene/carbon fiber/epoxy composites were prepared by autoclave co-curing molding process with graphene prepregs as the functional layer, which were paved on the surface of carbon fiber perform. The effect of graphene prepregs on the internal quality, electromagnetic interference shielding performance and mechanical properties of the composites was investigated by ultrasound scanner, metallograph, four-probe instrument, vector network analyzer and electronic universal material testing machine. The results show that the internal quality of the graphene/carbon fiber/epoxy composites will not be influenced by the addition of graphene prepregs, and there are a good interfacial compatibility between graphene functional layer and carbon fiber structural layer. On this basis, graphene prepregs, which serves as the functional layer, taking advantage of excellent electrical conductivity, can improve the electromagnetic interference shielding performance of the corresponding composites rapidly. With only one layer of graphene prepreg (G105/3234), electromagnetic interference shielding efficiency of carbon fiber/epoxy composites is improved from 27.7 dB to 64.7 dB. Meanwhile, the obtained composites still maintain satisfactory mechanical properties.
The residual stresses measured by photo-elastic method in cross section along the thickness direction of optical parts were compared quantitatively between injection molding and co-injection molding. The results show that the residual stress distributions of both injection molded slices and co-injection molded slices are double-parabolic shape, however, the latter has a higher stress level than that of the former. Besides, PC/PC and PMMA/PMMA disks by co-injection molding have no low-stress layer or zero-stress layer on both sides of the interface, on the contrary, there is a high stress peak at the interface. The stress in the PMMA layer of both PC/PMMA and PMMA/PC slices is increased gradually along the side surface toward the interface, which is different from the double-parabolic shape distribution of PMMA and PMMA/PMMA slices. The injection sequence of PC and PMMA layers has remarkable influence on the residual stress at the interface and in the PC layer of co-injection molded composite disks. The residual stress at the interface of PC/PMMA slices is significantly higher than that of PMMA/PC slices, and there still exists low stress layer and zero stress layer near the interface in the PC layer of PC/PMMA slices, while there are no such two stress layers in PMMA/PC slices.
In order to explore the quantitative characterization method of non-oriented acrylic sheet fracture and the correlation between the fracture morphology of acrylic sheet and tensile temperature. The non-oriented acrylic sheet for aircraft was used as the research object. Firstly, the size and surface roughness of the mist region were measured by stereo microscope and 3D Laster Scanner(LEXT). Secondly, the fracture was measured by box counting method. Finally, the energy consumed by the rupture of the acrylic sheet to form the mist zone was estimated by two hypotheses and was related to the fractal dimension of the fractured mist zone. The results show that when the stretching rate is constant, the stretching temperature is raised from -55 ℃ to 60 ℃, the size of the fractured mist zone ${\bar I}$3 is increased from 1.257 mm to 4.978 mm, and the surface roughness ${\bar R}$a is reduced from 0.517 μm to 0.330 μm, the fractal dimension ${\bar D}$is increased from 1.357 to 1.579. The fitting degree factors of the fitting curves of the tensile temperature and the size, surface roughness and fractal dimension of the fracture foggy area are higher than 0.9, and there fitting degree of these curves are higher. Therefore, the morphological parameters of the tensile fracture of the acrylic sheet have a certain correlation with the fracture conditions, and the energy consumed in the formation of the mist region of the acrylic sheet is positively correlated with its fractal dimension.
In order to study the influence of scanning strategy on the printing quality and properties of the formed parts, unidirectional scanning along one axis (X-scan), unidirectional scanning with 90° rotation in each layer (XY-scan), strip partition scanning strategy with direction changes in each layer (S-scan), checkerboard partition scanning strategy with direction changes in each layer (C-scan) were chosen to print 18Ni300 maraging steel by selective laser melting (SLM) process.The effects of different scanning strategies on the surface morphology, relative density, microstructure and mechanical properties of printed parts were studied systematically. The anisotropy of tensile properties of different scanning strategies in different forming directions was analyzed. The results show that the print quality and properties of the partition scanning strategies are better than that of X scanning strategy and XY scanning strategy. The reason is that during the printing process, the partition scanning strategy can divide each layer of laser scanning into multiple areas for printing, which improves the condensing rate for each layer. Compared with X scanning strategy and XY scanning strategy, the scanning direction of the partition scanning strategy changes periodically, which not only helps to fill the bulge and lap gap of the upper layer, but also reduces the heat accumulation and improves the performance of the sample.
The effects of low angle grain boundaries on the tensile properties and stress rupture properties of second generation single crystal superalloy DD5 at medium temperature and high temperature were investigated. The test plates were prepared by using seeds and processed into mechanical samples. The results show that the tensile strength at 760 ℃ is higher than 1100 MPa, the elongation is higher than 8% and the percentage reduction of area is higher than 14% when the angle is below 14.8°. The tensile strength, elongation and percentage reduction of area are decreased when the angle is above 14.8°. But the yield strength shows no difference. The tensile strength at 980 ℃ is higher than 760 MPa, the yield strength is higher than 630 MPa, the elongation and percentage reduction of area are decreased quickly when the angle is below 19.4°. The elongation is 1.4%, the percentage reduction of area is 2.8% when the angle is 19.4°. The rupture life at 870 ℃/551 MPa is higher than 110 h, the elongation is higher than 19.8% and the percentage reduction of area is higher than 23.1% when the angle is below 7.8°.But they are decreased quickly when the angle is above 7.8°.
The grain boundary engineering (GBE) treatment of heat treatment and cold rolling was adopted.The fretting wear behavior of Inconel 690TT alloy in air at room temperature and 320 ℃ was studied by OM, SEM, EBSD and white light interferometer. The results show that the proportion of low-∑ CSL boundaries of the best GBE sample is more than 70%, which is produced after 5% cold rolling, high temperature and short time annealing. The wear volumes and friction coefficients of the Inconel 690TT alloy samples at room temperature and 320 ℃ decrease with the increase of hardness and increase with the increase of grain size and low-∑ CSL boundary fraction. The fretting zone characteristic of Inconel 690TT alloy samples with larger grain sizes and higher proportion of low-∑ CSL boundaries under the same fretting experimental parameters is prone to full sliding, whereas it tends to partial sliding. Compared with grain size, the low-∑ CSL boundary fraction plays a more important role in determining the fretting behavior of GBE samples. The sample with higher fraction of low-∑ CSL boundaries has lower resistance to fretting wear, so GBE treatment is inimical to improving the fretting wear resistance of materials.
In order to prevent the damage of the connected electronic components at high temperature and improve the wettability of the commonly used low-temperature SnAgCu(SAC) solder on the surface of the base material 25%AlNP/Al(volume fraction) composite and 6061Al alloy, the Ni thin layer or the Ti/Ni bimetal thin layer on the surface of the base metal were pre-metallized by magnetron sputtering, and then connected with a SnAgCu solder, a well-bonded joints was obtained. After double metallization, the interface on both sides of the joint is composed of base material /Ti-Al/Ti/Ti-Ni/Ni/Ni-Sn-Cu/β-Sn+Ag3Sn. The difference in diffusion speed between different elements leads to differences in the phase composition of the interface reaction layer at different positions. From the Ni plating layer to the center of the weld, the phase of the reaction layer is (Ni, Cu)3Sn, (Ni, Cu)3Sn2, (Ni, Cu)6Sn5, (Ni, Cu)3Sn4. The addition of Ti element can significantly improve the bonding strength between the Ni-plated layer and the base metal. The joint shear strength of the joint material obtained by brazing the base metal after double metallization at 250 ℃ for 1 min to 5 min can reach 28-35 MPa, fracture occurs at β-Sn matrix.
Dry sliding wear tests and specially designed double sliding wear tests of TC11 titanium alloys were carried out at sliding velocities of 2.68 m/s and 4 m/s by using a MPX-2000 type pin-on-disc wear tester. The phase, composition and morphology of worn surfaces and tribo-layers were analyzed in detail by X-ray diffractometer, scanning electron microscope and energy dispersive spectrometer. The microhardness distribution from tribo-layers to the matrix was measured by using a digital microhardness tester. The results show that tribo-layers are always found to be formed on the worn surface of TC11 titanium alloy at different sliding rates. The phase, state and property of the tribo-layer vary with the sliding conditions. Tribo-layers can be divided into tribo-oxide layer and no-oxide tribo-layer. Through 4 m/s & 2.68 m/s double sliding wear test, the tribo-oxide layer formed in the dry sliding wear process of TC11 titanium alloy is proved to possess good wear-reducing effect. The wear mechanism of TC11 titanium alloy is delamination wear at 2.68 m/s, and oxidative wear at 4 m/s and 4 m/s & 2.68 m/s.
The bioactive coatings were prepared on the surface of Ti6Al4V by micro-arc oxidation in the electrolyte system consist of CaSiO3, Na2SiO3·9H2O, EDTA-2Na, K2HPO4·3H2O and the electrical parameters were fixed at 400 V, 600 Hz, 15%, 10 min with constant voltage mode. The value of concentration of CaSiO3 and Na2SiO3·9H2O were changed, and the range of change was 0.0835-0.15 mol/L and 0-0.06 mol/L respectively. Structural properties and microstructure of bioactive coating fabricated by micro-arc oxidation were detected by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), electrochemical workstation, eddy current thickness profiler, scratch tester and Image-Pro Plus 6.0. The effects of CaSiO3 and Na2SiO3·9H2O concentrations on the bioactive coating were studied. The results show that thickness, roughness, micropore diameter and porosity, calcium phosphate ratio gradually increase and corrosion resistance, bond strength gradually deteriorate with the increase of CaSiO3 concentration. Micropore diameter and porosity first grow larger and then become smaller, thickness, roughness, calcium phosphate ratio and bond strength gradually increase and corrosion resistance becomes better first and then deteriorates with the increase of Na2SiO3·9H2O concentration. The performance of the coating is the best when the concentrations of calcium silicate and sodium silicate are 0.15 mol/L and 0.015 mol/L, respectively.
Lithium-ion battery cathode materials of Mg doped Li1.2Mn0.6Ni0.2O2 were prepared by combustion synthesis. The phase structures and morphologies of the as-prepared samples were characterized by X-ray diffractometer, Raman spectroscopy and scanning electron microscope, respectively, and their electrochemical performance was measured. Results show that the as-prepared samples have better hexagonal layered structure, with spherical-like appearance. Through Mg2+ doping, the initial coulombic efficiency, cyclic stability and rate capacity are efficiently enhanced for the Li1.2Mn0.6Ni0.2O2 material. When the Mg2+ content is 0.02, the battery sample exhibits excellent electrochemical performance.
TiO2 nanowires were prepared on fluorine-doped tin oxide(FTO) glass by hydrothermal synthesis, and then the MoO3/TiO2 composite films were prepared by electrodepositing MoO3 films onto TiO2 nanowire arrays. The parameters such as diffusion coefficient(D), the responding time of colored and bleached, optical density(ΔOD), electrochromic reversibility and coloration efficiency of MoO3/TiO2 composite film were obtained by electrochromical measurement technologies and spectrum tests. The effect of TiO2 nanowire substrates with different hydrothermal growth time on the electrochromic properties of MoO3/TiO2 composite films was studied. The results show that the MoO3/TiO2 composite films with 6 hours of hydrothermal growth TiO2 nanowires have the best electrochromic properties. The diffusion coefficient is 2.86×10-12 cm2·s-1, the cyclic reversibility is 60.88%, the optical density is 0.41, the coloring efficiency reaches 124.49 cm2·C-1, and its responding time of colored and bleached is 13.53 s and 12.65 s.
A strategy based on grafting organocatalytic units as side-chain on the organic linkers, a TEMPO radical decorated terphenyl-dicarboxylic acid linker was synthesized. By employing acetic acid as modulator, TEMPO radical decorated UiO-68-TEMPO nanocrystals were synthesized by using H2tpdc-TEMPO as organic linker and ZrOCl2 as metal source under solvothermal conditions. UiO-68-TEMPO are monodispersed nanocrystals with side in the range of 800-1200 nm, with high BET areas (up to 1320 m2/g), and contain a large number of TEMPO radicals as evidenced by solid-state EPR spectrum. UiO-68-TEMPO nanocrystals enable selective oxidation of a broad range of alcohols, including primary aromatic alcohols, secondary aromatic alcohols, and heterogeneous atomic alcohols, with high efficiency and selectivity. The catalytic activity of UiO-68-TEMPO nanocrystals remains 75% after catalysis for four cycles. Finally, a plausible catalytic mechanism for the oxidation of benzyl alcohol by UiO-68-TEMPO was proposed, that is the TBN co-catalyst produces NO2/NO redox mediator, which enables the oxidation of TEMPO radicals to oxoammonium cations by O2, and finally oxidize benzyl alcohol to benzaldehyde.
By using industrial CT equipment, the three-dimensional digital volume image of the specimen of the 3D printing material before and after the deformation was obtained, and then the internal three-dimensional displacement field and three-dimensional strain field of the specimen were calculated by using digital volume correlation (DVC), from which the internal deformation and damage evolution of the specimen under load were studied. By designing and fabricating an in-situ loading device with 1700 N tensile and compress loading capacity, and combining it with micro-nano CT equipment, the DVC method test device with in-situ loading and observation capability was established, and the highest imaging resolution is 10 μm. The results show that when the in-situ tensile test is carried out on the 3D printing aluminum alloy specimen prepared by the laser selective melting (SLM) process, and the full field displacement and strain data inside the specimen are obtained by the DVC method, the elastic modulus data measured from cloud image is in good agreement with the results of conventional test methods. It is proven that DVC is an effective method for measurements of internal displacement field and strain field.
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