Abbreviation (ISO4): Journal of Materials Engineering
Editor in chief: Xiangbao CHEN
Aerogel/fiber composites have shown a wide range of applications in aerospace， defence， environmental management and biomedicine due to their high porosity， low bulk density， high specific surface area and low thermal conductivity.The thermal and mechanical properties and interfacial compatibility of aerogel/fiber composites was reviewed， the heat transfer mechanism， mechanical property enhancement mechanism and interfacial compatibility bonding mechanism was introduced， and the effect of different fiber embedding on the final properties of the composites considering different fiber volume fractions and fiber multiscale i.e. different fiber diameters （aspect ratio） and pore diameters between fibers was summarized in this paper. Finally， the prospective future of the research directions of aerogel/fiber composites were proposed， including heat resistance， improved mechanical properties and material interface bonding.
Narrow-band，high-color-purity luminescent materials are widely used in the fields of ultra-high-definition display and lighting，super-resolution imaging and sensing，bio-imaging and anti-counterfeiting. However，the high-color-purity fluorescent materials mainly used are Ⅱ-Ⅳ semiconductor quantum dots，halide perovskite nanocrystals and so on，which generally contains highly toxic transition metal ions such as Cd and Pb. Moreover，these materials often show low environmental stability. In contrast，carbon dots have many advantages including no heavy metal ions，high photo/chemical stability，low toxicity and wide source of raw materials. Therefore， developing fluorescent carbon dots with high-color-purity has important theoretical and practical significance. Here，the research progress of the synthesis and application of high-color-purity carbon dots was reviewed；the effects of precursor，synthetic methods and some factors on the position and the full width at half maximum of the carbon dots and the application in the field of LED， sensing and imaging were discussed. Additionally，the opportunities and challenges of high-color-purity carbon dots in large-scale synthesis，optical properties including the tune of PL position，the enhancement of the fluorescent quantum yield and color purity，understanding their photoluminescence mechanism as well as developing new applications were proposed.
Reactive oxygen species （ROS） as the substances with strong reactive activity， mainly include hydroxyl radicals （·OH）， superoxide anion radicals （· ） and hydrogen peroxide （H2O2）. Abnormal concentration of reactive oxygen species in mammals can cause serious diseases such as diabetes， cancer， tumors and some neurodegenerative diseases. Therefore， an increasing interest in the detection of ROS and issues was focused on and the consideration of the development of ROS detection sensors （e.g.， biocompatibility， stability of the detection method， variability of different types of ROS， etc.） were raised. In the past， electrochemical sensors based on natural enzymes have been developed， but the drawbacks of natural enzymes such as complicated preparation， difficult purification， poor catalytic activity and stability，which limit their research and application. In recent years， numerous studies have found that nano-mimetic enzymes have unique enzyme-like properties such as catalytic activity， selectivity and stability， which can be widely used to construct electrochemical biosensors for the detection of reactive oxygen species. Recent nano-mimetic enzyme sensors for the detection of · ， H2O2 and ·OH were focused in this paper， which are used in the field of life sciences to prevent related diseases in advance through the detection of reactive oxygen species， and can be used in the field of environmental pollution prevention and control for the quantitative detection of reactive oxygen species content.
Magnesium alloy as the most potential light structural material， has the advantages of high specific strength， specific stiffness and easy recycling， which contributes to the realization of lightweight in the industrial field. Compared with the traditional manufacturing technologies， the new and advanced manufacturing technology of additive manufacturing represent for high manufacturing efficiency， excellent performance， and forming complex structures. The technology of additive manufacturing for magnesium alloy， which has broad application prospects in the industrial field， is urgently required to be studied. In this paper， the recent studies of the three major additive manufacturing technologies for magnesium alloy：selective laser melting， wire+arc additive manufacturing， and friction stir additive manufacturing were summarized and analyzed from the aspects of forming characteristic， defect control， and features of microstructure and property.Finally，the developments in shape and performance control of the additive manufacturing technology for magnesium alloy：simulation analysis， process control， and heat source regulation were discussed.
The continuous casting mould is the most crucial core component of the continuous casting production line，which undertakes the important tasks of cooling，heat conduction，abrasion resistance and high-precision forming of the billet surface during the high-speed vibration drawing process of the molten steel. Based on the engineering application practice of mould surface protective coatings in domestic steel plants， the advantages，disadvantages and developing trends of electroplated alloy coatings and thermal spray coatings on the surface of mould copper plate were summarized，as well as the main failure forms and formation mechanisms at different locations of mould surface after service under actual working conditions，providing the basis for optimizing the design of coating compositions and corresponding performance in different areas. Moreover，the service results and application advantages of the thermal spraying/vacuum diffusion composite technology developed by the project team in major domestic steel plants were introduced in detail. Finally，it was pointed out that thermal spraying technology will gradually replace electroplating technology and become the core technology of mold surface protection，and high entropy and medium entropy alloy coating has great application potential.
The static and dynamic corrosion experimental platforms of supercritical fluid reactor were used for the static and dynamic corrosion test of Q235， 304， 316L， P91， N80 and 3Cr13 in the supercritical water pseudo-critical region （22.5 MPa， 375.6 ℃） and gas-like region （22.5 MPa， 407.6 ℃） for 72 h. The results show that the dynamic corrosion rate of materials in supercritical water environment is significantly higher than the static corrosion rate， and the flow accelerates the corrosion process， in which 304 is increased by more than 4 times； the strengthening effect of dynamic conditions on corrosion mass gain is weakened with the decrease of corrosion resistance. The factors that exacerbate corrosion under dynamic conditions are： flow shear force accelerates the movement of the corrosive medium in the supercritical fluid to the substrate surface， promoting the corrosion chemical reaction； the flow shear force scours the material surface， promotes the dissolution of Fe on the material surface， and accelerates the corrosion chemical reaction； the erosion effect of shear force promotes the detachment of corrosion product crystals during the formation process of the wall， accelerating the corrosion process.
Under certain solid solution time conditions， the solid solution temperature determines the degree of supersaturation and recrystallisation of the matrix after quenching， and is an important factor in enhancing the performance of the material after aging treatment. Through the solid solution heat treatment of 2050 Al-Li alloy extruded bar at different temperatures for 2 h and artificial aging treatment at 170 ℃ for 40 h， combined with a variety of property testing methods and microstructure observation methods， the effect of solid solution temperature on the microstructure and properties of 2050 Al-Li alloy extruded bar was studied. The results show that the residual phase is continuously redissolved with the increase of the solid solution temperature， and the residual phase is mainly iron-containing phase when the solid solution temperature is 525 ℃.The slight overheating structure appears in the bar when the solid solution temperature is 550 ℃， and the serious overheating structure appears in the bar when the solid solution temperature reaches 570 ℃. Local recrystallization occurs when the bar is heated to 500 ℃， and complete recrystallization occurs when the solid solution temperature reaches 570 ℃. When the 2050 Al-Li alloy extruded bars are solution treated at different temperature （450-550 ℃） and aged at 170 ℃ for 40 h， the number of θ′ and T1 phases increases with the increase of solid solution temperature， and the strength increases rapidly and then slowly，when the solution treatment temperature is 550 °C， the yield strength and tensile strength of extruded rods are the highest， which are 505 MPa and 567 MPa， respectively； the elongation decreases rapidly at first and then remains stable with the increase of solid solution temperature， decreasing from 13.4% at 450 ℃ to 10.7%-10.4% at 500-550 ℃.
Carbon fiber-reinforced Al-Mg-Ti laminated composites were prepared by vacuum hot-press diffusion technique and "foil-fiber-foil" method using 1060 pure aluminum， TC4 titanium alloy， AZ31 magnesium alloy and nickel-plated carbon fiber woven fabric as raw materials. The effect of Al-Mg diffusion layer thickness on the material tissue properties was analyzed by controlling the Al-Mg holding time， and the strengthening mechanism of carbon fiber was discussed. The phase composition， element distribution and crack extension morphology of the composites were analyzed by X-ray diffraction （XRD）， energy spectrum （EDS） analyzer and scanning electron microscopy （SEM）， and the flexural strength and impact toughness of the composites were tested. The results show that the thickness of diffusion layer of carbon fiber-reinforced Al-Mg-Ti laminated composites increases with the increase of holding time， and the mechanical properties show a trend of increasing and then decreasing， and the carbon fiber absorbs a large amount of fracture energy through fiber debonding， fiber pull-out and fiber splitting， which plays a significant toughening effect. The mechanical properties of the composites are optimal at the hot pressing temperature of 640 ℃ for 2 h for Al-Ti and 440 ℃ for 8 h for Al-Mg， with flexural strength of 380 MPa and impact toughness of 26.2 J/cm2， which are increased by 10.8% and 30.3% respectively， relative to the matrix flexural strength and impact toughness.
Using a high temperature solid state reaction at 1600 ℃ for 6 h， （Nd1－ x Ca x ）（Al1－ x Fe x ）O3－ x /2（x=0，0.1，0.2，0.3） was synthesized by introducing Ca2+ and Fe3+ into NdAlO3， and spark plasma sintering （SPS） ceramic samples were used to investigate the effects of Ca2+ and Fe3+ addition on the phase composition，emissivity and ferroelasticity of NdAlO3. The results show that a solid solution can be successfully fabricated through the high temperature solid state reaction. The doping of Ca2+ and Fe3+ in NdAlO3 increases oxygen vacancies and slight lattice distortion occurs，emissivity of NdAlO3 within the wavelength range of 2.5-10 μm increases the maximum to 0.9. The introduction of impurity ions makes the phase gradually transform from rhombohedral to cubic，leading to the ferroelastic domains vanish. However，the fracture toughness of ceramic samples remains at a high level.
In order to improve the interfacial wettability and adhesiveness between matrix and filler in the preparation process of azide-polyether based solid propellant and the processing property of the slurry， the effects of the kind of bonding agents and plasticizers and the ratio of plasticizers on the binding energy of 3， 3-diazide methyl epoxy butane and tetrahydrofuran copolymer （PBT） based matrix and ammonium perchlorate （AP） were calculated by using molecular dynamics calculation method. Three main crystal planes （011）/（201）/（210） of AP were considered. The results show that the rational plasticizers， plasticizer ratios and bonding agents can effectively improve the interface wetting characteristics of ammonium perchlorate and azide-polyether based solid propellants.The binding energy between ammonium perchlorate and PBT matrix system was the highest when dibutyl phthalate （DBP） is used as plasticizer， BUNE is used as bonding agent， and the plasticizer ratio is 0.6. The experimental results of contact angle were used to verify the calculation results. The main factors affecting the characteristics of the interfacial wettability between ammonium perchlorate and azide-polyether in solid propellant slurry were obtained， providing a guidance for improving the interface wettability and adhesiveness， and also the processing property of propellants.
The microstructure and performance homogeneity of 80 mm thick ultra-wide 7B50-T7751 plate with different widths and thicknesses were studied by means of mechanical testing machine and scanning electron microscope，and the fatigue properties were compared and discussed with 7050-T7451 plate. The results show that the ultra-wide 7B50-T7751 plate has excellent mechanical properties. In L and LT directions， the tensile yield strength of 1/2 thickness reaches up to 568 MPa and 545 MPa，and the tensile strength reaches up to 612 MPa and 591 MPa，the compressive yield strength reaches up to 575 MPa and 587 MPa，the fracture toughness in L-T direction and T-L direction reaches 30.16 MPa·m1/2 and 26.47 MPa·m1/2，respectively. The ultra-wide thick plate exhibits certain anisotropy at different width positions，the performance homogeneity in LT direction tends to be better than in L direction. Performance at different width positions with 1/4 thickness shows little difference，while the performance at the edge of 1/2 thickness is better than that of the center. No obvious texture exhibits at 1/4 thickness，however，the main textures at the center of 1/2 thickness are S texture and Brass texture， and the main textures at the edge are R texture，S texture and Brass texture. When the stress ratio is 0.06，the T-L anti-fatigue crack growth rate performance of ultra-wide 7B50-T7751 thick plate is better than 7050-T7451 plate with the same thickness. The fatigue limit of LT smooth sample （K t=1） is about 7.6% inferior than that of 7050-T7451 plate， while the fatigue limit of notch sample （K t=3） is about 3.7% higher.
Boron nitride nanotubes were prepared by ball milling and annealing method using boron oxide and ammonia as raw materials and iron or magnesium powder as catalyst. The effect of iron or magnesium content on morphology and yield of boron nitride nanotubes was studied. The results show that uniform fine boron nitride nanotubes can be obtained by annealing process when the precursor of boron oxide does not contain catalyst， but the yield is very low. Appropriate iron can play a good catalytic role， a large number of boron nitride nanotubes with uniform size can be obtained. With the increase of iron content， the productivity of the product decreases and the morphology of the annealed products changes from boron nitride nanotubes with uniform size to boron nitride nanotubes with uneven diameter and length. When the molar ratio of boron oxide and iron content reaches 1∶1， the productivity of the product increases and the morphology of them changes from smooth boron nitride nanotubes to coral-like boron nitride micro-nanostructures with a large number of boron nitride nanosheets growing vertically on the surface of boron nitride nanotubes， and the diameter of the product increases obviously. The change of magnesium content only affects the size， uniformity and productivity of the product， no effect on morphology was observed. Changes in morphology and yield of boron nitride nanotubes can be explained by gas-liquid-solid growth mechanism.
Planning of laser scanning path is the key process strategy of selective laser melting （SLM） additive manufacturing technology. Combining the significant structural characteristics of a three-dimensional model to realize process path planning is an important measure to improve the forming quality of parts. An SLM regional path planning method based on suspension recognition was proposed. By identifying the suspension characteristic region of the three-dimensional model， combined with the contour offset algorithm， the forming region segmentation and scanning path planning are realized. The effects of scanning line angle， interlayer rotation and different offset distance on the forming quality of suspension structure characteristics were studied by means of numerical simulation and process test. The results show that when the overhanging edge is offset by a reasonable distances and the scanning strategy parallel to the overhanging edge is adopted in this area， the deformation and residual stress on the overhanging edge can be reduced by 54% and 73% at most.
The self-healing oxidized sodium alginate-glycol chitosan hydrogel （OSA-GC） based on dynamic imine bonds was synthesized. Oxidized sodium alginate （OSA） was synthesized by oxidizing sodium alginate with sodium periodate， and self-healing OSA-GC hydrogels with different cross-linking degrees were prepared by Schiff base reaction with glycol chitosan （GC）. The effect of GC concentration on the microscopic morphology，viscoelasticity，swelling performance，self-repair performance， degradation rate and in vitro drug release performance of OSA-GC hydrogels were investigated. The results show that OSA-GC hydrogels have the characteristics of porous structure with a pore size ranging from 50 μm to 280 μm by controlling the mass ratio of OSA to GC. The OSA-GC hydrogels can reach the swelling equilibrium at 120 hours， and the swelling ratio reach 71.3-112.1. OSA-GC hydrogel can be degraded in PBS containing lysozyme （10 mg/mL）， and the mass loss of OSA-GC hydrogel is 43.1%-51.9% after 12 days. At room temperature， OSA-GC hydrogels can achieve self-healing within 2 h in the absence of external stimuli. OSA-GC hydrogel loaded with gemcitabine shows a sustained release effect on the anti-cancer drug gemcitabine， and the release time can reach 48 hours in the drug release experiment， which shows promising application prospects in biomedical fields of drug carriers.
The glass fiber fabric reinforced polytetrafluoroethylene （GF/PTFE） self-lubricating composite was investigated by using a high frequency and high load oscillating friction and wear tester MYB-500 to carry on a whole life wear test. The self-lubricating performance and damage characteristics were studied， and the wear debris and wear surface were analyzed by microscopic detection method to discuss the key factors affecting the self-lubricating stability and service life of material. Results show that the life cycle of GF/PTFE self-lubricating composite exhibits an obvious stage characteristics， and can be divided into three stages， including running-in， stable stage and failure stage based on the change of friction coefficient and wear depth. Real-time monitoring of friction coefficient and friction temperature can effectively reflect the self-lubricating performance and life stage of the material. The change of wear depth and wear surface analysis show that the wear exhibits notable non-uniformity. According to wear mechanism， the inhomogeneity of the initial thickness of the material has a significant influence on the inconsistency of the damage during the wear process as well as its life. Therefore， by improving the curing process， the stable stage in life cycle can be prolonged and the service life of the material can also be increased.
Cr-Ni resource-saving Sn-containing ferritic stainless steel （FSS） was taken as the research object. The microstructure evolution and properties change of the experimental steel under different hot rolling processes were explored by means of optical microscope（OM）， electron backscattering diffraction（EBSD）， X-ray diffraction（XRD）， room temperature tensile test， electrochemical corrosion test， etc. The results show that when the finishing rolling temperature （FRT） is in the range of 940-730 ℃， properly reducing the FRT has a significant role in refining the grains of hot-rolled and annealed sheets and final cold-rolled and annealed sheets， as well as increasing the orientation density of recrystallization texture， and thus the yield strength， tensile strength and elongation are significantly increased. When the FRT is 800 ℃， the tensile strength is 509 MPa， the yield strength is 331 MPa， and the elongation reaches a maximum of 42%， and meanwhile， the maximum cupping value and plastic strain ratio are obtained， leading to the best mechanical properties. In addition， the pitting potential and self-corrosion potential are increased， while the corrosion current density and corrosion rate are decreased by properly reducing the FRT. When the FRT is 800 ℃， the pitting potential reaches the maximum， the corrosion current density reaches the minimum and corrosion rate reaches the lowest， thus the optimum corrosion resistance is obtained in the steel. The properties of Sn-containing FSS are significantly improved compared with SUS430 FSS by optimizing the hot rolling process.
The BNNS-CNT/PVDF composite film with high in-plane thermal conductivity and insulation was prepared by using the strategy of hybrid synergy and orientation enhancement of different thermally conductive fillers. The boron nitride nanosheets（BNNS）/polyvinylidene fluoride（PVDF） fiber film by electrospinning was first prepared， and then surface sprayed carbon nanotubes（CNT） and multi-layer film hot pressing were used. Electrospinning technology enables BNNS to achieve in-plane orientation in PVDF films. The sprayed CNTs build an efficient thermal conduction path between the film layers and bridge the BNNS in the adjacent fiber films， which promotes the construction of in-plane thermal conduction network， but still maintains good insulation performance. As a result of the optimization of film preparation conditions， the in-plane thermal conductivity of the BNNS-CNT/PVDF composite film with 30%（mass fraction，the same below） BNNS and 3%CNT content reaches 3.25 W∙m-1∙K-1， which is 1104% higher than that of pure PVDF. Meanwhile， the film has an ultralow out-of-plane conductivity of 2.09×10-12 S∙cm-1. It is found that BNNS and CNT synergistically build an efficient thermal conductivity network， and the enhancement efficiency of 3%CNT for BNNS/PVDF is as high as 52.2% at 5%BNNS filling. At the same time， the thin film has good tensile strength and flexibility.
In order to improved the defects of xylan-based films such as strong hygroscopicity and low mechanical strength， a collaborative modification protocol of citric acid （CA） and MPTMS-modified xylan （MSMX） was proposed. Xylan from sugarcane bagasse was firstly modified by （3-mercaptopropyl）trimethoxysilane （MPTMS）， and then citric acid was used as crosslinking agent or plasticizer. The MSMX/PVA/CA films were prepared by casting method and the effects of citric acid content on the structure and packaging performance of the composite film were studied. The results show that with the increase of CA content， the cross-linking degree of MSMX/PVA/CA films increases and the internal structure becomes more dense， which lead to the significant enhancement of mechanical properties and water vapor barrier performance. Meanwhile， the hydrophobicity of the MSMX/PVA/CA films is improved with the decrease of hydrophilice groups. When CA content is 20% （mass fraction）， the tensile strength of MSMX/PVA/CA film is 41.8 MPa， water contact angle is 82°， and the water vapor transmittance reaches 2.79×10-13 g·cm·cm-2·s-1·Pa-1， which is 37.79% lower than that of film without CA. The addition of CA improves the moisture barrier properties and mechanical strength of xylan composite films， which makes it have a potential application in the field of food and drug packaging.
In order to improve the preparation process and practical process of magnetic refrigerant， a method of accelerating phase formation by cold compression plastic deformation at room temperature was proposed. The grain structure， phase composition and magneto-thermal effects of La0.6Pr0.4Fe10.7Co0.8Si1.5 alloy were systematically studied. The results show that with the increase of compression ratio， the number of grains per unit area increases and the grain size is uniform. Compared with the uncompressed sample， the proportion of magnetothermal phase increases after annealing under the same conditions. When the compression rate is 30%， the ratio of 1∶13 phase after 3 days annealing is 92.68%（volume fraction）， and the pre deformed sample is obviously better than the undeformed sample.After annealing for 3 days， the Curie temperature （T C） of 30% pre-deformed La0.6Pr0.4Fe10.7Co0.8Si1.5 is 289 K， and the magnetic entropy change （ΔS max） is -7.1 J/（kg·K） under 2 T magnetic fields.The suitable Curie temperature and value of ΔS max make it an attractive potential candidate for the room temperature magnetic refrigeration application.
Molten pool monitoring is the basis of forming process optimization， playing a pivotal role in improving the formation quality. A machine vision monitoring system was set up for the laser cladding process. Based on the OpenCV software library， a method combining K-means image segmentation and dual threshold Otsu image segmentation was proposed， which realizes the accurate distinction between molten pool and plume with the accuracy of extracting geometric features of molten pool contour up to 95%. By designing an orthogonal experiment of laser cladding Ti-6Al-4V metal powder， typical cladding samples were selected to analyze the width and shape change of the weld pool in time domain， obtaining the fluctuation rule of the weld pool of the cladding layer. The results show that the fluctuation frequency and amplitude of the molten pool are affected by the process parameters and their combinations， and gradually stabilize with the progress of the cladding. Abnormal fluctuations in the molten pool during the cladding process are conducive to the positioning and identification of cladding defects， helping to optimize process routes.
With the development of the Internet of Things， the rapid development of miniaturized self-powered electronic products and further micro-modulation greatly stimulate the urgent demand for microscale electrochemical energy storage devices. In each electrochemical energy storage device， the supercapacitor based on the plane pattern shape is highly compatible with modern electronic products in terms of functional features such as miniaturization and integration. In this work， the flexible 3D interdigital electrode symmetric micro capacitor was prepared by the combination of semiconductor preparation technology and electrophoresis printing technology， and the 3D printing was carried out by using oxygen enriched activated carbon ink. The 3D interdigital symmetric electrode was prepared by adjusting and optimizing the electric field strength， line width， number of printing layers and other parameters. The energy dispersive spectrometer （EDS）， scanning electron microscopy（SEM），rheometer，electrochemical workstation and test system were used to characterize materials， pastes and microcapacitor devices， and to explore the influence of materials and pastes on the performance of 3D interdigital microcapacitor. The results that the 3D interdigital supercapacitor prepared by the combination of semiconductor and electrophoresis printing process has good performances， and its area capacitance can reach 22.3 mF·cm-2. In addition， the device can achieve 96% capacity retention after 2000 cycles through packaging optimization. This simple and controllable 3D jet printing technology provides an effective way to prepare advanced miniaturized electrochemical energy storage devices.
ISSN 1001-4381 (Print)
Started from 1956
Published by: AECC Beijing Institute of Aeronautical Materials
