Pure copper/copper alloy has excellent thermal and electrical conductivity, which is an important industrial material. Laser powder bed fusion, which represents the laser additive manufacturing technology, has excellent design freedom and forming accuracy, and is the mainstream development direction of additive manufacturing. Compared with traditional processing and manufacturing technology, the laser powder bed fusion of pure copper/copper alloy can give better play to the excellent performance of copper, and has broad application prospects in the fields of high thermal conductivity/electrical conductivity such as electrical and electronic, automotive, aerospace and other fields. The current research status of laser powder bed fusion of laser high-reflective materials represented by pure copper/copper alloys, the important problems they face, and the analysis of corresponding solutions were reviewed in this paper. On this basis, combined with the team's experience in the laser powder bed fusion process of pure copper/copper alloy, it was pointed out that the use of blue, green and other short-wavelength lasers for the powder bed laser fusion of pure copper/copper alloy and other highly reflective materials is a future study hot spots and development directions.
Additive manufacturing technology as revolutionary manufacturing technology has attracted much attention.This technology transformed traditional processing design and manufacturing concepts and promoted the development of intelligent manufacturing. Intelligent material is a kind of material that has the ability of self-perception, autonomous response, self-healing and adaptation. The combination of intelligent materials and additive manufacturing technology can realize the integrated manufacturing of three-dimensional smart devices with the ability to sense external stimuli or environmental activation. This technology has been widely used in fields such as biomedical devices, flexible electronics, soft robotics, and other fields.Additive manufactured intelligent materials, and the advantages and problems of additive manufactured intelligent materials of metals, polymers, and ceramics were reviewed.As a technical means to realize the organic integration of design, material and structure, additive manufacturing technology will become the key to promote the development of intelligent materials.
AlxCoCrFeNi(x=0.3,0.5,0.7,1.0)high-entropy alloy was fabricated by selective laser melting (SLM),and pre-alloyed powder was prepared by gas atomization.The phase composition, microstructure, hardness, Young’s modulus and creep curve of AlxCoCrFeNi were comprehensively analyzed through X-ray diffractometer, scanning electron microscope and nanoindentation experiments, respectively. The influence of Al content on the microstructure and nanoindentation of AlxCoCrFeNi was discussed.The results show that Al0.3CoCrFeNi and Al0.5CoCrFeNi are FCC structure, while Al0.7CoCrFeNi and Al1.0CoCrFeNi are BCC/B2 structure. The microstructure of Al0.3CoCrFeNi and Al0.5CoCrFeNi are mainly composed of equiaxed crystals, while Al0.7CoCrFeNi and Al1.0CoCrFeNi are mainly composed of columnar crystals. It indicates that the content of Al has great influence on the microstructure of AlxCoCrFeNi high-entropy alloy.With the increase of Al content, defects such as pores and cracks in the specimens increase. There is no obvious molten pool morphology observed in Al0.3CoCrFeNi and Al0.5CoCrFeNi. The residual stress increases with the increase of Al content. The hardness and Young’s modulus of the samples were measured. It was found that with the increase of Al content,the hardness of the sample increases from 447HV to 567HV.The Young’s modulus of Al0.3CoCrFeNi is about 273 GPa, and Al0.5CoCrFeNi is about 233 GPa,while Al0.7CoCrFeNi and Al1.0CoCrFeNi are about 240 GPa and 242 GPa,respectively. The changes in hardness and Young’s modulus are mainly related to the microstructure and phases of specimens. Different from the traditional creep curve, the creep curve of AlxCoCrFeNi includes only two stages, which are instantaneous creep and steady-state creep. The creep mechanism is mainly dislocation creep. Among the samples, Al0.7CoCrFeNi has the best creep resistance. Al0.3CoCrFeNi has the best print formability, with the yield strength of 702 MPa, and the elongation is 27.5%.
Selective laser melting (SLM) was used to prepare LaB6 particle-reinforced titanium matrix composites(PRTMCs), the influence of laser energy on the densification behavior, phase, microstructure and the corresponding mechanical properties under quasi-static and impacting conditions were studied.The results show that the densification behavior of Ti-6Al-4V alloy is changed to some extent by the introduction of LaB6 particles, and the density of PRTMCs is reduced by either too high or too low laser energy input.Significant grain refinement happens after the addition of LaB6 particles, the grain boundary of the initial β and acicular α is weakened.As a consequence, the yield stress and ultimate compressive stress of the PRTMCs are enhanced but the ductility is weakened to some extent, meanwhile, PRTMCs exhibit obvious strain rate strengthening effect.Compared with the SLMed Ti-6Al-4V, the strain strengthening effect in the plastic deformation stage and brittle fracture characteristics in the instability stage of PRTMCs become more notable.Through this study, a theoretical basis for the dynamic compressive performance of laser additive manufactured PRTMCs can be provided.
Resin matrix composites have many advantages such as high specific strength and modulus, good fatigue performance, corrosion resistance, and have become the application and development trend of aero engine components under 400 ℃. Foreign research on resin matrix composites for aero engine started earlier, which have been applied in fan blades, fan casings, outer ducts, nacelles and other components of multi-engine, and developed towards the trend of better structure, higher material performance, lower manufacturing cost and higher automation degree. The development foundation of domestic resin matrix composites is good, but compared with foreign countries the application proportion of resin matrix composites in engines in not high. It is necessary to furthur improve the technical level of design, materials, manufacturing, experiment and engineering ability. In this paper, foreign development status was discussed in the field of structures, materials and processing methods of aero engine composite components, the development trend was analyzed and corresponding suggestions were given, from the aspects of building composites system for aero engine, strengthening application research and design guide, promoting the transformation of pre-research achievements and application of automation technology.
In most cases, friction and wear are not conducive to mechanical equipment. As a large country in machinery manufacturing, reducing friction and wear is of great significance to industrial progress and sustainable development. Ceramic-based composite coating is one of the common systems in industrial applications. It uses ceramic materials as the matrix and dopes with lubricating materials as the second phase. On the one hand, it inherits the excellent high temperature stability and strength of the ceramic phases; on the other hand, it improves the lubricating performance in the common friction environment. Therefore, it is widely used in ships, aerospace, biotechnology and high speed trains, etc., and it has received extensive attention and exploration by researchers. Ceramic-based high-temperature self-lubricating composite coatings were focused on in this paper. First, the basic classification of coatings and solid lubricating materials were explained. Then the present researches progress was reviewed, meanwhile, the influence of process parameters on the performance of ceramic-based high-temperature self-lubricating coatings and improvement methods were focused on. Hence the key factors for improving the surface tribological properties of ceramic-based high-temperature self-lubricating composite coatings were summarized, and the feasibility or research potential of improving the friction reducing and wear-resistant performance was discussed. Finally, the current shortcomings of ceramic-based high-temperature self-lubricating composite coatings were summarized in two points: (1) the phase analysis of composite coatings is still focusing on the phenomenon, and without complete theoretical basis; (2) the methods for improving the structure and tribological properties of composite coatings under different preparation processes are relatively simple. Therefore, the corresponding solutions and possible development orientation were proposed preliminarily: (1) further explore the synergistic mechanisms between the ceramic-based and different lubricating phases, additional components, high temperature environment, and establish the theoretical basis of the system; (2) for the different forming mechanisms of preparation processes, the influence of the synergistic effect of process parameters on the microstructure of the composite coating needed to be focused on, expanding the improvement method of the preparation process.
Carbon nitride has the advantages of excellent thermal stability, high thermal conductivity, larger forbidden band width and negative electron affinity. Therefore, carbon nitride is a promising field emission cathode material. On the basis of introducing the structure and properties of carbon nitride and its research status as a field emission material, the preparation methods of carbon nitride films and powders were emphatically reviewed in this paper. Then the methods to improve the field emission performance of carbon nitride were discussed from the following aspects: optimizing the number and size of sp2 clusters, texture modification, elements doping and forming hybrid field emitters by compounding with other field emission materials or surface modification. In the end, the problems that still exist in the carbon nitride films and powders as field emission cathode materials were summarized respectively. Based on this, the focus of future researches on field emission of carbon nitride was concluded, which is to continue to optimize its field emission performance, and to explore the influence of its internal structure and defects on the field emission performance.
Buoyant materials, as an important counterweight material of the deep-sea devices, play an important role in providing the equipment with enough buoyance as much as possible. Solid buoyant materials (SBMs) have received extensively attention in deep-water surveying and development and petroleum exploration fields in recent years due to their low density, high strength and low water absorption characteristics.In this paper, the classification and the application of SBMs and their recent developments both at home and broad were firstly discussed. Typically, the SBMs can be mainly divided into the chemical and the composite syntactic foams according to their chemical composition and the composite syntactic foam was especially elaborated in this study. Secondly, four basic types of the composite syntactic foams, namely metal-, polymer-, and ceramic- matrix and other types of the syntactic foams, based on their chemical composition of the matrix and the reinforcement. The influence factors such as the essential composition, the surface microstructure, and the loading rate on the physical, mechanical, and the failure mode of the syntactic foams were summarized. The dynamical behavior and failure mechanism under different loading rates can be analyzed and revealed by the computed X-ray tomography technique combined with the finite element method. The prospects of improving overall mechanical performance and advanced experimental characterization methods of syntactic foams are summarized as follows: the overall mechanical performance can be improved by modifying functional groups of filler and resin matrix or adding a second reinforcement phase; the microstructure can be characterized and the failure mechanism revealed by means of μ-CT and scanning electron microscope.
Nano-sized Dy2O3 doped ZrO2 powders (DySZ) were synthesized by cocurrent co-precipitation method. The effects of Dy2O3 content, cation concentration, pH value and calcination temperature on the phase composition, crystal structure, grain size and micromorphology of DySZ powders were investigated. Results show that under different synthesis conditions, the spherical DySZ powders have nano scale characteristics with a size range of 10-30 nm, Dy2O3-doping can promote the DySZ stabilized as tetragonal structure. The doping amount of stabilizer has a significant effect on the phase composition of DySZ powder. Single tetragonal DySZ can be obtained with 10%(mass fraction) Dy2O3-doping. No significant effect can be found between the tetragonality, microstructure of DySZ powders and the stabilizer content, cation concentration, pH value as well as calcination temperature. The average grain size exhibits a slight decrease with the increase of stabilizer content, cation concentration and pH value. Meanwhile, the elevated calcination temperature can promote the crystal growth of DySZ.
Three kinds of porous transition metal oxide materials, Fe2O3, Co3O4 and CoFe2O4, were successfully prepared by oxalate-routed pyrolysis method. The crystal structure, morphology, specific surface area, magnetic property and surface chemical state of those materials were characterized by XRD, SEM, BET, VSM and XPS, respectively. The catalytic performance towards PMS activation for degradation of simulated printing and dyeing wastewater were evaluated, taking a typical cationic dye methylene blue(MB) as the degradation model. The results show that all the three materials present hierarchical micro/nano porous fibrous structure, and a much higher PMS activation performance of CoFe2O4 is observed comparing with Fe2O3 and Co3O4 due to its highest specific surface area as well as the concerted catalytic effect between iron and cobalt elements. Through a series of single-factor experiments, the optimal process conditions for MB(10 mg·L-1, 500 mL) degradation in CoFe2O4/PMS system are determined as follows: PMS dosage of 3 mL(0.1 mol·L-1), catalyst dosage of 0.07 g and reaction time of 50 min. Under this reaction condition, MB removal rate of 89.77% can be achieved. Meanwhile, effect of common anions on CoFe2O4/PMS advanced oxidation system is also investigated. It is found that the presence of Cl-, PO43- and C2O42- all exhibit inhibition for MB degradation in different degrees. Besides, quenching experiments and electron paramagnetic resonance (EPR) identification results both confirm that 1O2 is the primary active specie in CoFe2O4/PMS advanced oxidation system. Furthermore, the recycling experiments indicate that CoFe2O4 presents a long-term stability. More importantly, CoFe2O4 can be easily separated from liquids after the reaction with an external magnet owing to its good magnetic property. The results demonstrate that CoFe2O4 is a promising catalyst candidate in activating PMS to degrade dyeing wastewater.
PC/PCCD blends with different PCCD contents were prepared by melt blending. The optical performance test results show that PC/PCCD blends have high light transmittance and low haze. SEM, TEM, DSC, FTIR, 1H NMR and 13C NMR spectra test have been used to investigate PC/PCCD to reveal the internal mechanism of the optical transparency of the blends. The results show that PC/PCCD has a homogeneous structure at the scale of tens of nanometers, which is the direct reason for its high optical properties. All PC/PCCD blends with different PCCD contents show a single glass transition temperature, indicating that PCCD and PC are completely compatible. This complete compatibility leading to the homogeneous structure is the inherent reason for the high transparency of PC/PCCD blends. The mechanism of compatibility between PCCD and PC was further analyzed, and the results show that no transesterification reaction occurs during the melt blending of PC and PCCD. The compatibility of PC and PCCD results from the similarity between their molecular structure, and has nothing to do with whether the transesterification reaction occurs.
In order to prepare capacitor materials with low cost, higher specific capacitance and better cycle stability, the graphene-based nickel-containing metal organic framework material (Ni-BTC/RGO) was prepared by electrochemical method to study the synthesis conditions of Ni-BTC and the electrochemical properties of Ni-BTC/RGO. A series of Ni-BTC materials under different conditions were analyzed by XRD. SEM, cyclic voltammetry and constant current charge-discharge tests were carried out for Ni-BTC, RGO and Ni-BTC/RGO. The results show that working voltage of 6 V, reaction time of 3 h, and reaction system temperature of 35 ℃ are optimum synthesis conditions of Ni-BTC; Ni-BTC and RGO are successfully combined and RGO has no effect on the structure of Ni-BTC; the composites mainly exhibit pseudocapacitive electrochemical behavior. At the current density of 0.5 A·g-1, the specific capacitance of Ni-BTC/RGO is 468.72 F·g-1, and the power density is 0.249 W·g-1; after 500 cycles at the current density of 1.0 A·g-1, the specific capacitance retention rate is 50.08%.
Without adding any interlayers or coatings, the lap welding experiment of AZ31B magnesium alloy and DP980 high-strength steel was performed with the laser-induced tungsten inert gas welding (TIG) arc technology. Through optimizing the process parameters, a high-quality lap weld joint was obtained. The effect of TIG arc current on the forming and mechanical properties of the joint was studied significantly. The results indicate that the wetting and spreading ability of magnesium alloy in high-strength steel is improved with the increase of arc current, which increases the weld width and reduces the wetting angle. Additionally, the maximum tensile load of magnesium alloy/steel welded joints increases first and then decreases with the increase of arc current and the fracture mode of the joint is changed from fracture along the interface to fracture along the weld. When the TIG current is 80 A and the laser power is 350 W, the maximum average tensile load of the welded joint reaches 279 N/mm.The increase of weld width, thickness of interfacial layer and pinning of laser keyholes together enhance the performance of magnesium alloy/steel joints.
Corundum-based (Al2O3) refractory materials prepared by powder metallurgy superalloy powder were heat treated at 950-1350 ℃ for 60 min in order to study the effect of temperature on the microstructure and particle shedding of corundum-based refractory materials. The phase structure of the refractory materials before and after heat treatment was analyzed by XRD. Scanning electron microscopy (SEM) with energy dispersive spectrum (EDS) was used to characterize the microstructure and phase composition of the refractory samples. In addition, the adhesion experiment was used to evaluate the particle shedding of the refractory materials after heat treatment at different temperatures, and explore the mechanism of pre-heating treatment reducing the possibility of particle shedding. Thermal shock test was used to evaluate the thermal shock resistance of refractory materials after heat treatment at different temperatures. The apparent porosity and bulk density were measured. The results show that with the increase of preheating temperature, the composition of calcium aluminate cement binder in refractories is gradually changed from CaAl2O4 (CA) to CaAl4O7 (CA2), and the fine ceramic particles in refractories are sintered together until the interconnected network structure is formed. With the increase of preheating temperature, the fine refractory particles in the refractory are gradually wet and spread on the large particles as aggregated and connected to form a network structure, and finally the large particles are coated. The particle adhesion of refractory gradually increases with the increase of heating temperature. The heat treatment has minor effect on the apparent porosity, bulk density and heat shock resistance of the refractory materials. However, with the increase of heating temperature, the local peeling degree of the refractory surface and mass loss rate in the thermal shock test are significantly improved. The particle shedding is obviously reduced whereas preheating for 60 min at 1150-1350 ℃, and the relative suitable preheating temperature is in the range of 1250-1350 ℃.
In order to study the fatigue properties of 2024 aluminum alloy under different corrosion fatigue conditions, First, an in-situ corrosion fatigue platform was established, and then non-corrosion fatigue test, pre-corrosion fatigue test and in-situ corrosion fatigue test were used to comparatively study the fatigue life and fracture mechanism of 2024 aluminum alloy. Scanning electron microscopy(SEM) was used to characterize the macro and micro fracture characteristics and explore the failure mechanism. The results show that the samples with the same corrosion environment and corrosion time, the fatigue life in in-situ corrosion fatigue test and in pre-corrosion fatigue test is 92% and 42% of corrosion fatigue life, respectively. Under the condition of in-situ corrosion fatigue, the squeeze and the extrusion of slip zone leads to the increase of surface roughness, which adsorbs more corrosive medium, exacerbates pit evolution, accelerates the initiation of crack and forms multiple crack sources. The connection of cracks forms a larger size of damage, and rapidly expands inside the material. A lot of brittle fringes are observed in the fracture of the pre-corrosion and in-situ corrosion fatigue test specimens, and the average distance between the fringes under in-situ corrosion fatigue is about two times larger than that under non-corrosion fatigue, indicating the crack propagation rate is faster under the in-situ corrosion fatigue condition.
To investigate the microstructure and magnetic properties of hot-rolled industrial pure iron during annealing, X-ray diffraction and magnetic hysteresis analysis were performed. The evolution of dislocation density, and magnetic parameters, i.e. the maximum permeability, coercivity, and remanence, were analyzed respectively. Results show that the near equiaxed grain structure of industrial pure iron has no obvious change before and after annealing, and the grain size number is about 3.70. With the annealing time increasing to 5 h at 650 ℃, the dislocation density gradually decreases from the hot-rolled state of 1.80×1014 m-2 to 1.16×1014 m-2, with an amplitude of 35%. At the same time, the diffraction peaks are observed to shift to the left to a certain extent compared with the hot-rolled state, and then to the right. It indicates that the existence of residual compressive stress in micro scale and a subsequent releasing process. The shape of the magnetic hysteresis loops is narrow and changes little with the increase of annealing time. However, the maximum permeability shows a continuous increment, and some abrupt changes are observed in the coercivity and remanence.This might be attributed to the comprehensive influences of dislocation density, internal stress and carbon content. It is indicated that annealing treatment could improve the magnetic properties of industrial pure iron. With a further consideration of the effects of impurity elements, an integrated strategy of composition and microstructure control will improve the ferromagnetic performance of industrial pure iron and expand its electromagnetic applications.
In order to explore the influence of the physical crosslinking network structure of polyborosiloxanes(PBDMSs) on the viscoelasticity of the system, hydroxyl terminated polydimethylsiloxane (PDMS) with different hydroxyl contents were reacted with boric acid to prepare PBDMSs with different boronization crosslinking densities. Thereafter the structure, thermodynamics and rheological properties of the as prepared samples were characterized. The results show that PBDMSs contain Si—O—Si, Si—O—B, CH3—Si—CH3 and B—O—B structural units. And PBDMSs have excellent low temperature resistance, while their glass transition temperature increases with the increase of hydroxyl content in PDMS. And at low hydroxyl content of PDMS (1% and 2%, mass fraction), crystallization of PBDMSs are observed. Moreover, PBDMSs possess the characteristics of frequency sensitivity, good impact resistance, excellent damping dissipation and excellent resilience. The hydroxyl content of PDMS obviously affects the physical crosslinking network structure of PBDMSs, and thus has a significant impact on the dynamic modulus of PBDMSs. In practical application, the viscoelasticity of PBDMSs can be adjusted by changing the hydroxyl content of PDMS.
Stress-strain curves are of great significance in studying the changes of work hardening, dynamic recrystallization and dynamic recovery of metal during hot deformation, and predicting the stress-strain curves under different thermal deformation parameters is helpful to study the machinability and instability of metal in hot working process. The thermal deformation behavior of Nb-V-Ti microalloy steel was studied by hot compression experiments at strain rates of 0.01-3 s-1 and deformation temperatures of 1000-1200 ℃ on Gleeble-3500 thermal simulation testing machine. The BP neural network model and GA improved BP neural network model were established to predict the stress-strain curves at the strain rate of 0.5 s-1 and deformation temperature of 1050 ℃, and the strain rate of 1 s-1 and deformation temperature of 1100 ℃. The results show that the BP neural network model improved by GA is in good agreement with the stress-strain curves of the test data and the experimental curves. The correlation coefficients are 0.99202 and 0.99734 respectively, and the errors are only 2.7816% and 2.1703%. The relative errors between the predicted results and the experimental results are within the range of [-2, 2]. It is proved that the model is reliable and applicable to a wide range of strain, which provides theoretical guidance for rolling process in industrial production.