- 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)
NiTi-based shape memory alloys (SMAs) are one of the SMAs with most outstanding properties, and have been widely applied in aviation, space, electronics, construction, biomedicine and other fields. In recent years, the elastocaloric refrigeration based on elastocaloric effect (eCE) of NiTi alloys has attracted increasing attentions since their excellent mechanical properties, huge elastocaloric strength and good machinability. However, conventional binary NiTi alloys cannot meet the requirements of long-life service since their large superelastic stress hysteresis and poor cyclic stability of superelasticity and eCE. In this paper, the research progress of eCE for NiTi-based alloys was reviewed. The effect of doping alloying element, thermomechanical treatment and novel processing techniques on eCE of NiTi-based alloys were surnmarized. In addition, the developed elastocaloric devices or prototypes based on NiTi-based alloys were also briefly introduced. However, the current researches on NiTi-based elastocaloric materials and the development of prototypes are still in the experimental stage. To realize their commercial application requires further in-depth research and optimization. In the future, the research priorities for the former will concentrate on material miniaturization, alloying or applying special treatment as well as changing circulation methods and so on. On the other hand, the research priorities for the latter will focus on improving heat transfer efficiency, strengthening heat exchange, reducing friction and other losses, and improving mechanical loadings as well as circulation modes.
The irradiation effect is the change of microstructure and macroscopic properties caused by the interaction between incident particles and materials. Irradiation effect is not only an important method to modify the surface of materials, but also an essential part of the reliable evaluation of materials applied in special environment. The TiNi based shape memory alloy is a kind of important intelligent material, which has the unique shape memory effect and superelasticity and can be widely used in spacecraft such as satellites, space stations and biomedical science. The spacecraft will be irradiated by charged particles mainly including protons, electrons and ions. The irradiation effect can influence the microstructure of TiNi based shape memory alloy, which will change the phase transformation and mechanical behavior. However, the current investigation in irradiation effect of TiNi based shape memory alloy is still in its infancy. The change rules and mechanism of microstructure and phase transformation have not been studied clearly. And there are few studies on the effect of irradiation on the shape memory effect have been carried out. In-depth study on the irradiation parameters, microstructure, phase transformation behavior and functional properties is still needed.
Ni-Mn-based magnetic shape memory alloys have excellent shape memory effects induced by the temperature field and magnetic field, superelasticity, magnetocaloric effect, magnetoresistive effect, elastocaloric effect, exchange bias effect, etc. As a new type of multi-functional material, it is expected to be used in many engineering fields such as actuators, sensors and so on. The research status of Ni-Mn-based magnetic shape memory alloys containing the second phase was described in detail. The formation of the second phase and its influence on martensitic transformation, functional performance and mechanical properties were summarized. Several important and unresolved issues currently were presented, such as the impact of the second phase on magnetic functional properties including magnetic shape memory effect. It was pointed out that in future work, it is essential to study the thermodynamic and kinetic factors of the formation and evolution of the second phase, and properly regulate the second phase so as to optimize the functional properties of the alloys.
Ti-Ni-Hf alloy is one of the most potential high temperature shape memory alloys due to the various advantages such as higher phase transformation temperature, relatively lower cost and larger output work. However, the plastic deformation takes place prior to the reorientation of martensitic variants due to the lower matrix strength, which results in the poor shape memory properties. To date, the measures of improving the strain recovery characteristics consist of thermo-mechanical treatment (cold rolling + annealing), alloying, aging treatment and fabrication of single crystal etc. It has been revealed that the strain recovery performances of Ti-Ni-Hf alloys are closely related to the microstructural features. In the present paper, the recent progress in the field of Ti-Ni-Hf high temperature shape memory alloy was presented, mainly consisting of microstructural evolution, martensitic transformation behaviour, mechanical properties and strain recovery features, moreover, the relationship between the microstructure, martensitic transformation as well as the mechanical and strain recovery characteristics was established, based on the previous research results. At present, the poor cold or hot workability of Ti-Ni-Hf high temperature shape memory alloy is the bottleneck which limits its extensive applications. Hence, the future research may focus on the powder metallurgy and additive manufacturing of Ti-Ni-Hf high temperature shape memory alloy.
Polycrystalline Ni-Mn-Ga-Fe fibers were prepared by melt-extraction technique. The internal stress and defects introduced by rapid solidification were modified by step-wise chemical ordering annealing. The microstructure and phase microstructure of fibers were characterized using Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscopy (TEM) and XRD diffraction technique. The phase transition behavior and two-way shape memory effect (TWSME) were tested using Dynamic Mechanical Analyzer (DMA). The results show that after heat treatment, the chemical ordering degree is increased, and the martensite twin boundaries are straight. Complete recoverable strains of parent and martensite phases during thermal cycles are achieved. During the two-way shape memory cycles, two characteristics of thermoelastic martensite transition are displayed in heat-treated fibers: reversibility and thermal hysteresis. In the thermal cycle test, the total strain reaches 1.32% when the fiber is loaded to 198 MPa. The thermomechanical tensile measurement shows that the phase transition temperature follows the Clausius-Clapeyron equation. Compared with other alloys such as Ti-Ni and Cu-Al-Ni, Fe-doped fiber exhibits a smaller strain-stress dependence, which is beneficial to the constant strain output.
Li-rich manganese cathode material(LMCM)is considered to be the most promising cathode material for the next generation of Li-ion battery due to the advantages of high specific capacity (>250 mAh·g-1) and low cost. However, due to factors such as irreversible structural transformation of the cathode material during cycling, these materials suffer from many problems including high first irreversible capacity loss, energy decay, poor rate performance and voltage decay. The problems of LMCM can be partially improved by lattice doping, coating modification and structural optimization design, and the electrochemical performance as a cathode material for Li-ion batteries can be improved. This paper focuses on the primary problems and modification research work of LMCM. The causes of the problems existing in LMCM were firstly analysed. Then, the current research status of the main modification methods was elaborated. Meanwhile, the advantages and disadvantages of each modification method were discussed while the future research directions were pointed out. The current industrialization process and major challenges of LMCM materials were also discussed.Due to LMCM's problems and the slow development of supporting materials, it is only produced in small batches in a few enterprises at present.
Li4Ti5O12 (LTO) anode materials are successfully prepared by sol-gel method using butyl phthalate and lithium acetate as precursors.The phase and morphology of the material were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The effects of calcination conditions and coating modification on transport properties of LTO were also studied.The results show that the ionic conductivity and electronic conductivity of the sample prepared at 800 ℃ and 10 h are 8.8×10-8 S/cm and 8.53×10-10 S/cm, respectively. The ionic and electronic conductivities of LTO/C are 4.35×10-7 S/cm and 9.63×10-8 S/cm, respectively.The electrochemical performance tests show that the first discharge capacity of carbon-coated active materials can reach 172.4 mAh/g at the ratio of 0.1 C.After 50 cycles at 5 C, the capacity retention rate can reach 94.4%, indicating a good electrochemical performance of the samples.
The isothermal deformation behavior of Ni-Cr-Mo low alloy SA508Gr.4N steel at deformation temperature of 850-1200 ℃, strain rate of 0.001-1 s-1, and true strain of 0.9 was studied by using Gleeble-1500D thermal simulation testing machine.The physically based flow stress model including dynamic recovery and dynamic recrystallization and the dynamic recrystallization grain size model were established, and the suitable forging process to avoid the coarse grain structure heredities was put forward.The results show that as the deformation temperature increases and the strain rate decreases, the dynamic recrystallization volume fraction and grain size gradually increase; the true stress-true strain curve of SA508Gr.4N steel has an obvious discontinuous dynamic recrystallization phenomenon; by comparing the experimental value with the predicted value of the model, the correlation coefficient (R) and mean relative error (MRE) of the flow stress model are 0.998 and 4.76%, respectively, and the correlation coefficient (R) and mean relative error (MRE) of the dynamic recrystallization grain size model are 0.991 and 8.69%, respectively. The two models have high accuracy.
Hot compression properties of aluminium cladded 7B04 composite sheets were investigated by thermal simulation testing at the deformation temperatures of 380-450 ℃ and strain rates of 0.1-30 s-1. The results show that the instability zone of hot processing map gradually expands to the region of high strain rates with the increase of true strains. The most suitable hot working zone is at the temperature range of 380-410 ℃ and strain rate of 5-30 s-1. Electron backscattered diffraction (EBSD) technique was employed to study the deformed microstructure. The results show that the recrystallized grains tend to have flat boundaries and the orientation difference between grain boundaries increases gradually with the increase of temperature and the decrease of strain rate. During deformation, the Al-clad layer shows mainly continuous dynamic recrystallization, while discontinuous dynamic recrystallization and continuous dynamic recrystallization (including geometric dynamic recrystallization) co-exist in the 7B04 matrix. The optimal hot deformation temperature of materials are 410 ℃ at the strain rate of 10 s-1, at this moment, the grain size of both 7B04 matrix and Al cladding is close and small.
Mg-12Gd-3Y-1Sm-0.5Zr alloy was prepared by induction melting, and the microstructure and properties of the alloy after heat treatment at different aging temperatures were analyzed by X-ray diffraction(XRD), optical microscope(OM), transmission electron microscopy(TEM), micro-hardness and tensile test. The results show that the alloy grain size gradually increases with the increase of aging temperature, the number of the second phase in the grain increases, and the time during which the hardness peak appears gradually decreases when Mg-12Gd-3Y-1Sm-0.5Zr alloy is peak aged at 200, 250 ℃ and 300 ℃. The precipitated phase is β' when the aging temperature is 200 ℃ and 250 ℃, and the precipitated phase is β phase when the aging temperature is 300 ℃. The mechanical properties of the alloy peak aged at 250 ℃ are the best. In the process of stretching at room temperature, 200, 250 ℃ and 300 ℃, the tensile strength of the aging peak alloy at 200 ℃ and 250 ℃ shows the abnormal temperature effect of increasing at first and then decreasing, but while no such abnormal phenomenon appears in the alloy after peak aging heat treatment at 300 ℃.
The plastic shear resistance of commercially pure titanium (TA1) surface is low and the protective effect of oxide film is limited. Serious wear behavior will occur during sliding friction. The friction and wear behavior of TA1 disc treated by high temperature oxidation was studied by means of high temperature friction and wear tester, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).The results show, because of the lubrication effect of abrasive debris, under the same load and wear time, the friction coefficient of TA1 with oxide layer ranges from 0.07 to 0.3, and that of TA1 without oxide layer ranges from 0.55 to 0.9.The higher the friction and wear test temperature is, the more and deeper the furrow morphology distribution is at the friction area of TA1 with oxidation layer. For TA1 specimens without oxide layer, with the increase of temperature and the prolongation of grinding time, cracks are easier to propagate and form delamination wear. The main wear modes of TA1 material are delamination wear, adhesion wear and oxidation wear. The adhesion wear of TA1 material without oxide film and oxygen-rich layer is more serious. Different surface hardnesses and wear mechanisms result in different friction and wear properties at high temperature.
Four different types of silica particles (A200, H2000, R812S, T36-5) were used as reinforcing fillers for EPDM to prepare microcellar EPDM foams by supercritical CO2. The viscoelasticity, vulcanization and cell structure of different silica were tested and characterized by scanning electron microscope and rubber processing analyzer. The results show that the EPDM matrix has good rheological property with fumed silica (A200, H2000, R812S) as reinforcing filter, which is conducive to the formation of cell structure and the cell density is increased with the increase of the degree of crosslinking. The modulus and viscosity of the EPDM matrix with silica T36-5 matrix as the reinforcing filler by using precipitation method are too high, therefore the cell structure is formed only in narrow pre-vulcanization interval. Among them, the EPDM matrix with silica A200 as the reinforcing filler can obtain a high degree of cross-linking without losing good rheological properties, and A200 can provide better heterogeneous nucleation, and significantly improve cell density and reduce cell size.
Improving the extraction and separation rate of electron-hole couple in photocatalysis is one of the key technologies to improve the catalytic performance of photocatalysts. Flower-like g-C3N4/BiOBr positive and negative (P-N) heterojunction composite were prepared by in-situ method using graphite phase carbon nitride as basic dopant, which was obtained by stripping bulk carbon nitride with concentrated sulfuric acid. The effect of pH value on morphology of g-C3N4/BiOBr composite was studied. Crystal structure, morphology and composition properties were characterized by X-ray diffraction(XRD), scanning electron microscope(SEM), energy disperse spectroscopy(EDS), transmission electron microscope(TEM), ultraviolet-visible(Uv-vis) and specific surface area(BET). The results show that heterojunction is established between g-C3N4[002] facets and BiOBr[001] facets inside g-C3N4/BiOBr composites, accelerating the collect and separation of the photo induced electron(e-)-hole(h+) pairs. Graphite phase carbon nitride reduces the band gap width of g-C3N4/BiOBr composites to 2.71 eV, compared with BiOBr to 2.75 eV, which can expand the light absorption range. Beside, the specific surface area of BiOBr and g-C3N4/BiOBr are 1.27 m2/g and 6.43 m2/g, which means increased reactive side. The photocatalytic activity of g-C3N4/BiOBr composite is better than pure g-C3N4and BiOBr, which also shows high efficiency when reused. g-C3N4/BiOBr composite has best photocatalytic performance with pH=8, its degradation rate of orange yellow G, rhodamine B and methyl orange are 91.00%, 95.51% and 96.72%, respectively.
Reducing NOx emission in the exhaust gas under the extremely low temperature of engine cold start was important for the ecological environment and human health.MnO2 has high catalytic activity for NOx in the low temperature range, which is a promising nanocatalyst.The intrinsic relationship between the surface structural characteristics and denitrification activity of MnO2-Fe2O3-CeO2/Al2O3 nanocatalysts produced by ultrasonic assisted coprecipitation method with different manganese contents was discussed. The results show that when the manganese content is 15%(mass fraction), the nanocatalyst has the largest specific surface area and the smallest grain size. At the same time, the distribution of active substances is the most uniform. Meanwhile, the crystallinity of metal oxides is suppressed, and Mn, Fe and Ce are in the best coexistence state, which can promote the enrichment of chemisorption oxygen. The catalytic oxidation of NO to NO2 improves the reaction rate of fast SCR, and the NO2 conversion reaches 88.5% at 50 ℃. Optimizing manganese content is an extremely effective method to improve the structure-activity relationship of catalytic materials and promote the performance of NO preoxidation and fast SCR reaction.
The homogeneous dispersion of the raw materials is the key process to prepare 3Y-ZrO2/Al2O3 ceramics. In engineering, the three-roller mixing is suitable for dispersing the high viscosity slurries containing the fine ceramic powders, which benefited reducing the amount of dispersion medium and drying time. The commercial 3Y-ZrO2 powder (80 nm) and two kinds of Al2O3 powders (3 μm and 0.3 μm) were used as the starting materials. 3Y-ZrO2/Al2O3 composite ceramics were prepared by three-roller mixing, die pressing, and sintering. The relation of phase compositions, microstructures, and bending strengths of the ceramics was investigated by XRD, SEM, and universal testing machine. The results show that the microscopic aggregation area of Al2O3 grains with the maximum size of 5-10 μm exists in the 3Y-ZrO2/Al2O3 composite ceramics in addition to the normal dispersed phase of Al2O3 and the continuous phase of 3Y-ZrO2. The transition from the tetragonal to the monoclinic phase of 3Y-ZrO2 occurs with the addition of coarse Al2O3 powders. However, the tetragonal phase shifts to the right with no monoclinic phase detected in the samples with fine Al2O3 powders. The proper addition of the two Al2O3 powders is beneficial to achieving the maximum bending strength when the 3Y-ZrO2/Al2O3 ceramics are sintered at 1600 ℃. However, the curve change of the bending strength of the composite ceramics with fine Al2O3 powder is smoother than that of the samples with coarse Al2O3 powder with the increase of Al2O3 volume fraction.
In order to develop a binderless phase cemented carbide to reduce the application of cobalt in conventional cemented carbides, (W, Mo)C/Al2O3/La2O3 were prepared by chemical methods. Ammonium paratungstate, ammonium molybdate, aluminum nitrate, lanthanum nitrate, urea and glucose were used as raw materials to explore the different ratios of nitrate, urea and glucose by low temperature combustion method, and the optimal ratio of carbon was obtained to prepare (W, Mo)C/Al2O3/La2O3powder.The (W, Mo)C/Al2O3/La2O3 binderless phase materials were prepared by SPS sintering at 1500-1800 ℃.The mechanical properties were studied and the strengthening and toughening mechanism was analyzed. The results show that the optimum molar ratio of nitrate to urea is 1:2, the optimum molar ratio of nitrate to glucose is 1:0.5, the grain size is reduced by 0.28 μm after adding glucose, and the specific surface area is increased by 75.64%.Density, Vickers hardness and flexural strength reach maximum at 1600 ℃: 98.45%, 2202HV30 and 1203 MPa, respectively, and the fracture toughness reaches a peak of 7.52 MPa·m1/2 at 1500 ℃. (W, Mo)C/Al2O3/La2O3 are mainly intergranular fracture and transgranular fracture due to the influence of grain refinement and toughening of the second phase particles at 1500-1600 ℃; the reason why (W, Mo)C/Al2O3/La2O3 is mainly intergranular fracture at 1700-1800 ℃ is grain growth and the appearance of pore.
The resource utilization of solid waste is an important way to achieve energy saving and emission reduction. A lauric acid (LA)/raw fly ash (RFA)-diatomite(DT)/carbon nanotubes(CNT) composite form-stable phase change materials (FSPCM) for thermal energy storage were prepared via simple direct impregnation method, in which LA, RFA-DT binary matrix and CNT were employed as phase change materials(PCMs), the supporting material, and thermal conductive additive, respectively. The loading capacity, structure and thermal properties of FSCPCM were investigated through the diffusion-oozing testing, Fourier transform infrared spectrometer (FTIR), differential scanning calorimetry (DSC), thermo gravimetry analysis (TGA) and paperless recorder, respectively. The results show that the RFA-DT binary material can effectively prevent the leakage of LA. When the mass fraction of LA in composite is 28%, the FSPCM without leakage can be obtained. What's more, the utilization rate of RFA reaches 55%. The FTIR demonstrates that FSPCM has good compatibility between its four components, LA, RFA-DT, and CNT. The melting onset temperature of FSPCM is 45.79 ℃ measured by DSC, and the corresponding latent heat of FSPCM is determined as 51.06 J/g. TGA analysis shows LA/RFA-DT has good thermal stability. The storage/release performance curve indicates that when mass fraction of CNT is added with 5%, the melting and solidification time of LA/RFA-DT/CNT are decreased by 60% and 62.5%, respectively, indicating that the heat transfer performance is remarkably improved.
Diatom is a natural active amorphous material. A diatom-based ion-imprinted composite adsorption material was prepared by the surface ion imprinting technology with diatom as matrix, mercaptopropyltrimethoxysilane(MPS)as the functional monomer, Cd(Ⅱ)as the template ion, and epichlorohydrin(ECH)as the cross-linking agent. The changes in surface morphology were characterized by SEM.The process of diatom surface fabric transformation was studied by XPS and FT-IR. The results show that the hydrolyzed MPS and the diatom surface active silane hydroxyl group are combined by dehydration condensation, and this process introduces the functional group (—SH) into the diatom surface. The ECH and —SH form network imprinted-sites under the effect of cross-linking. Combined with XPS semi-quantitative analysis, the formula for the degree of grafting of MPS on the surface of diatom is derived, and the grafting mode of the diatom-based Cd(Ⅱ) ion-imprinted composite adsorbent is determined. The grafting method of MPS on the surface of diatoms is mainly single-grafting, and accompanied by double-grafting; and the mechanism of adsorption between SH/DE-ⅡP and Cd(Ⅱ) ions is through the coordination of the lone pair of S atoms of MPS with Cd. The adsorption mechanism between SH/DE-ⅡP and Cd(Ⅱ) ions is the coordination of Cd with the lone pair of electrons.These lone pairs of electrons come from the S atom on —SH.The selective adsorption results show that the diatom-based Cd(Ⅱ) ion-imprinted composite adsorbent can selectively adsorb Cd(Ⅱ) ions. The removal rate of Cd(Ⅱ) ions in aqueous solution has increased from 24.4% to 97%, and it has the ability to directionally remove Cd ions.
The montmorillonite/Fe3O4/humic acid composite (MFH) was prepared by hydrothermal method. The effects of pH value, MFH dosage, adsorption time, initial concentration of U (Ⅵ) and temperature on the adsorption of U(Ⅵ)by MFH were investigated. The experiment shows that the dosage of MFH has the greatest influence on the adsorption of U(Ⅵ) within the selected test conditions; when the initial concentration of U(Ⅵ) is 5 mg·L-1, the pH value is 6, and the dosage of MFH is 0.3 g·L-1, and the temperature is 30 ℃, the removal of U(Ⅵ) by MFH reaches the adsorption equilibrium after 30 min, and the adsorption rate reaches 97.7%. The adsorption of U(Ⅵ) by MFH conforms to the quasi-second-order kinetic model and Langmuir model; the removal mechanism of MFH to U(Ⅵ) is complexation and reduction. The adsorption-desorption tests show that the adsorption rate of U(Ⅵ) by MFH composites is still as high as 90% after 5 cycles. The test shows that MFH has a good removal efficiency and efficient reusability for U(Ⅵ).
Gradient aluminum honeycomb structure is an effective energy-absorbing structure. According to the concept of gradient rate, four types of aluminum honeycomb sandwich components with the same mass and different gradient rates were designed by changing the cell wall length of the honeycomb core layer. On the basis of the same mass, the deformation mode of gradient aluminum honeycomb sandwich structure under quasi-static state, as well as the dynamic response and energy absorption characteristics of layered homogeneous honeycomb structure under impact load and layered gradient honeycomb structure with different gradient rates were compared by combining quasi-static compression experiments and the deformation and mechanical properties of gradient aluminum honeycomb sandwich structures under quasi-static and impact states, which were simulated by nonlinear finite element. The results show that during the quasi-static compression process, the deformation of the aluminum honeycomb gradient sandwich panel has obvious localization characteristics. The deformation of the honeycomb core is preferentially low density until compaction, and the densification strain difference between the layers is gradually decreased as the core layer density is increased. Besides, under high-speed impact, the gradient honeycomb panel is not strictly deformed step by step in the quasi-static process until it is densified. It is the linear elastic deformation, elastic buckling, plastic collapse and compaction that occur as a whole under the interaction of the hammer head inertia and the core layer density. In addition, during the range of the gradient rate designed in this paper, when the gradient rate is γ1=0.0276, the energy absorption of the gradient honeycomb sandwich panel is the best. Compared with a homogeneous honeycomb sandwich panel of the same mass, the energy absorption is improved by 10.63%.
|
Founded in 1956 (monthly) ISSN 1001-4381 CN 11-1800/TB Sponsored by AECC Beijing Institute of Aeronautical Materials |
