Hypersonic flight technology is an important direction in the development of aerospace field and plays an important role in national defense security. The thermal protection materials and structures are the key to the safe service of hypersonic vehicles in extreme environments. On one hand, the thermal protection materials and structures must be able to withstand the harsh aerodynamic thermal environment, and on the other hand, they also must reduce its mass to increase the vehicle payload. Therefore, it is necessary to develop thermal protection structures that can combine high temperature resistance, light weight, and load-bearing characteristics at the same time. The manufacturing methods of lightweight C/SiC ceramic matrix composite structures were firstly introduced in this review, then the research on the room temperature and high temperature mechanical behavior, heat transfer mechanism and behavior of the lightweight C/SiC ceramic matrix composite structures were summarized. At last, integrated thermal protection structures with high temperature resistance and lightweight load-bearing were reviewed based on the lightweight C/SiC ceramic matrix composite structures. Finally, the future challenges of the lightweight ceramic matrix composite structures towards thermal protection application were also forecasted in four aspects: new design theory and method, new manufacturing technology, service characteristics and multi-functional integrated design and realization. This review provides some guidance for the research and development of novel thermal protection structures for the next generation hypersonic flight.

To meet the requirements of high energy density and fast charge for energy storage systems and electric vehicles, the high-energy and high-power density lithium-ion batteries have attracted numerous attentions.Designing thick-electrode can significantly increase energy density and reduce cost, and is also compatible with various electrode materials, which makes it one of hottest researches for the development of high-energy density lithium-ion batteries.Thick electrodes usually suffer from poor mechanical properties and sluggish reaction kinetics. Therefore, it is very important to construct a thick electrode with good mechanical properties and fast transport network for lithium ion and electron.The electrochemical behavior and key scientific issues of thick electrodes were firstly analyzed in this review, the current strategies for constructing thick electrodes and their advantages were then introduced, and finally the design principles and the development direction of thick electrodes were pointed out.

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.

Interface is a key factor affecting the comprehensive performance of magnesium matrix composites, and how to carry out interfacial modulation has been a hot research topic in magnesium matrix composites. Focusing on three types of interface structures of magnesium matrix composites (coherent, semi-coherent and incoherent) and two key issues (interfacial wettability and interfacial reaction) affecting the interface properties, the research progress of interface optimization schemes was reviewed in this paper and the guidelines for the design and regulation of interfacial structures to achieve good interfacial bonding were proposed: good wettability and slight interfacial reaction. In view of the improvement of interface properties of magnesium matrix composites, the addition of rare earth elements can be considered in the future to purify the interface and improve wettability. The matrix and reinforcement are selected according to engineering needs to obtain composite materials with excellent performance in certain aspects. New reinforcement surface coatings will be developed to fully enhance the capabilities of interfacial bonding. First-principles and other computational simulation methods will be used to deeply explore the relationship between interface structure and interface performance.

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^-, PO₄^3- and C₂O₄^2- 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.

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.

In recent years, carbon-ceramic matrix composite materials have become a hot topic due to their high temperature resistance, low density, good corrosion resistance, low thermal expansion coefficient, and strong performance design. Biomorphic carbon-ceramic composites have been prepared by introducing the wood-derived pore structure into ceramic matrix.The pore structure, preparation process, properties and application prospects of biomorphic carbon-ceramic matrix composites were reviewed. The importance of designing the microstructure of materials was emphasized, and the key technology in the preparation process of carbon-ceramic matrix composites-infiltration technology were specified, including: chemical vapor infiltration, melt infiltration, sol-gel infiltration, slurry infiltration, polymer precursor infiltration, and molten salt infiltration. The solutions to the existing problems of each technology were proposed. Composite strength and fracture strength of biomass carbon-ceramic matrix composites were reviewed. Suggestions for future research directions on the performance were put forward. It was pointed out that the mechanical properties of materials should be tested under high temperature, strong acid and strong alkali, and alternating cold and heat environments. The potential applications of biomorphic carbon-ceramic matrix composites were discussed in three aspects, including aero-engine blades, automobile exhaust gas purifiers, and catalyst carriers. Existing challenges and practical limitations such as complex molding, strong mechanical properties and thermal stability were outlined. Finally, the improvement of the preparation process and the study of mechanical properties of biomorphic carbon-ceramic matrix composites were prospected, which provides theoretical basis and guidance for the development and application of biomorphic carbon-ceramic matrix composites.

Infection after surgery is one of the common and most challenging clinical problems, and the development of new antibacterial coating is an effective strategy to solve this problem, which has important scientific and social significance. A bioactive coating with antibacterial function was prepared on the surface of a 3D printed porous titanium bone scaffold. It is discovered that silver (Ag) exists in the coating as a simple substance. As the Ag content increases (0%, 0.5%, 1%, 1.5%, mole fraction), the specific surface area of the mesoporous coating is decreased from 377.6 m²/g to 363.35 m²/g. In vitro mineralization results show that with the increase of Ag content, the apatite inducing ability is decreased slightly. At the same time, the antibacterial test demonstrates that the addition of silver markedly enhances the antibacterial performance of the scaffolds. Adding a small amount of silver (0.5%) can achieve 100% antibacterial rate. The MC3T3-E1 cells are cultured with the scaffolds for 1, 3 and 7 days, and it is found that the Ag-doped MBG coatings have good cyto-compatibility, and the addition of a small amount of silver can promote the proliferation of MC3T3-E1 cells. A simple dipping and pulling method was used to apply the Ag-doped MBG coating to the complex 3D printed titanium scaffolds with complex topological structure. The mineralization performance, bactericidal performance and cellular compatibility of the scaffold are significantly improved, providing a new idea for the further development of multifunctional bone implant scaffold.

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.

Thermoplastic polyether ether ketone (PEEK) composites are widely used in aerospace field due to their excellent fracture toughness, impact resistance and material versatility. Sizing agent as the core auxiliary product of carbon fiber has an important impact on the interface of composites. Limited by the decomposition temperature, the traditional thermosetting sizing agents are difficult to meet the use of PEEK composites, which restricts the development and application of high-performance PEEK composites. Therefore, it is of great significance to develop a matching carbon fiber sizing agent for PEEK composites. In this paper, the interfacial properties of composites and the action mechanism of sizing agent were analyzed and introduced; the research progress and results of modified PEEK, polyimide precursor and polyetherimide sizing agents were focused, and different systems of sizing agents were analyzed and summarized.Finally, the relevant suggestions on carbon fiber sizing agents for PEEK composites were put forward while the environmental and multi-function developments for sizing agents were prospected.

With the rapid development of the new energy automotive industry, consumers' requirements for the range of electric vehicles have been increasing. The Ni-rich ternary lithium-ion battery has become the most promising power battery in electric vehicles due to its high specific energy, but the battery system still faces the problem of poor performance at low temperature.The research progress on low temperature performance of Ni-rich ternary power battery in recent years was summarized in this review. The influence factors on the low temperature performance of Ni-rich ternary power battery were summarized emphatically. On the one hand, the effects of low temperature performance from thermodynamics were analyzed, including the structural change of the Ni-rich ternary cathode materials and graphite anode materials, electrolytic phase transformation and solvation structure changes, and glass transition of binder. On the other hand, rate controlling step in the low temperature discharge process in the Ni-rich ternary lithium-ion battery was summed up. According to this, main modification measures of low-temperature performance in Ni-rich ternary power battery were summarized. Low temperature electrolyte was designed by optimizing solvents, improving lithium salts and applying new additives. In order to improve the low temperature performance of electrode materials, three methods were mainly employed: substitution, surface modification and smaller material particle size. The remaining shortcomings of the research on low-temperature performance of the battery were summarized, and the research on the low temperature thermodynamic characteristics of batteries is not clear enough. In addition, the research methods for the low temperature kinetic process of batteries are single, and the influence of the reaction sequence in batteries is insufficiently understood.

In order to investigate the solidification microstructures in typical section dimensions of a third generation single crystal superalloy DD9 turbine blade with 1500℃ and 1540℃ mould temperatures during directional solidification process, Optical microscopy (OM) and scanning electron microscopy(SEM) were used to analyse the solidification structure of typical sections of the blade. The results show that with increasing mould temperatures, the dendrite patterns have a tendency of becoming more refined, and the secondary dendritic arms tend to be highly developed. With the same mould temperature, the dendrite patterns in the blade aerofoil section are more refined than those in the tenon section. Also with increasing mould temperatures, the γ' precipitates of the interdendritic regions and the dendritic cores tend to be refined, the γ' precipitation size dispersion decreases, and the size distributions of the γ' precipitates follow the normal distribution law. Compared with the interdendritic regions, almost 61% reduction of the γ' precipitation average sizes is measured in the dendritic core. With the same mould temperature, the γ' precipitation sizes in the aerofoil section are more refined than those in the tenon section. Compared with the decreasing sectional areas, the increasing mould temperatures bring down the γ' precipitation sizes obviously. The sizes and contents of the γ-γ' eutectics decrease with increasing mould temperatures. The morphologies of γ-γ' eutectics show both sunflower-like shape and plate-like shape.

Continuous fiber reinforced and toughened ceramic matrix composites (CMCs) are key thermal structural materials in aerospace and other fields. Mechanical connectivity, as one of the most reliable connectivity methods, is an essential method to achieve connectivity of large and complex CMCs components. At present, research on CMCs joints is rapidly developing, but there is few comprehensive review literature on CMCs joints. Based on the research work in the field of CMCs joints in recent years, the preparation and mechanical property characterization methods of CMCs fasteners were summarized in this paper, the damage and failure mechanism of CMCs fasteners were systematically stored and discussed, and focusing on the influencing factors and laws of mechanical properties of CMCs fasteners from the perspective of material properties and external environment. The research work on CMCs mechanical joints was presented, and the damage law, failure mechanism, finite element simulation and reliability of CMCs connectors were prospected.

Aiming at the problem that surface cracks occur in the service of 15Cr2Mo1 heat resistant steel welds, NiCrFe alloy which was similar to the usage scenarios of this steel was employed to repair welds with different groove depths simulating crack depths. The feasibility of repair process was verified by the microstructure and performance characterization of the welds. The results show that repair welding at different groove depths is well formed and has no obvious defects, the weld metal is composed of austenitic cell dendrites and second phase precipitates, and there are a small amount of eutectic ferrite near fusion area, however, there is no ferrite in the bright white strip between the type Ⅱ boundary and the melting boundary. The increase of repair welding filler mainly reduces the yield strength of the joint, especially when the groove depth increases from 6.5 mm to 13 mm, the yield strength at room and high temperature is both greatly reduced by about 15%, then the decline trend slows down. With the increase of filler amount, the impact toughness of the fusion line and the 2 mm area outside the fusion line is improved, while the hardness of the whole weld decreases first and then increases with the increase of filler amount, which is related to the restraint of the repairing weld and the increase of precipitates formed by alloy element segregation.

Advanced oxidation process based on sulfate radical (SO₄^-·) is recognized as one of the effective methods to degrade organic wastewater. In recent years, as an economical and readily available carbon containing material, biochar has been gradually applied in the advanced oxidation field. Biochar and its composite activated persulfate have become a promising system for organic pollutants degradation. The latest research progress of different typical biochar-based catalysts for persulfate activation was analyzed, including pristine biochar, transition metal loaded biochar, non-metallic doping biochar, and metallic and non-metallic co-doping biochar. In addition, the synthesis methods and physicochemical properties were summarized. Furthermore, the activation performance and mechanism of biochar-based catalysts for persulfate and the degradation mechanism of organic pollutants were discussed, respectively. Finally, based on the current research progress, from the perspectives of different biomass sources, metallic and non-metallic co-modified biochar technology and the dynamic change of ecotoxicity in the degradation process, relevant discussions and future suggestions for biochar and its composites were put forward in terms of degradation mechanism exploration, potential catalyst development and practical catalytic system application.

Aiming at the need of aero-engines, investigation was made into the curing process and thermal stability of a polyimide-matrix structural composite. The curing kinetic equation of EC-380A resin was established. The curing degree of the resin was simulated as a function of the curing temperature and time. Further, combined with the resin rheology, the curing process of the EC-380A composite was established and verified. Large-scaled aero-engine typical structural components were fabricated. Thermal stability of the composite was estimated by mass loss, internal quality of the flaw-embedded laminate, and mechanical property after thermal ageing. By multi-temperature step curing at 330-380℃, the flaw-free composite could be manufactured under the circumstance of an integrated layup. The composite has excellent thermal stability with thermal resistance of 370-400℃. The mass loss rate is around 1.3% after ageing for 1000 h at 370℃ and 285℃.No new flaw or propagation of the embedded flaw occurs for the composite after thermal ageing at 400℃, indicating a high-temperature structural stability.

High-strength aluminum alloys (2××× and 7×××, etc.) are widely used in aerospace, automobile and other fields because of their high specific strength and good machinability. With the development of high thrust-weight ratio engine and automobile lightweight technology, the demand for lightweight structural materials is increasing. Meanwhile, parts also present the "thin-walled, hollow and composite" tendency gradually, and the traditional processing methods of high-strength aluminum alloy are increasingly difficult to meet the requirements. As a common metal additive manufacturing (AM) technology, selective laser melting (SLM) is a great potential manufacturing technology for complex parts. SLM is expected to become an emerging technology to expand the application of high-strength aluminum alloys. However, due to their poor casting and welding properties, high-strength aluminum alloys easily produce the periodic hot cracks and coarse columnar grains during SLM, leading to unsatisfactory mechanical properties. Grain refinement is the key to overcome the inherent hot-tearing crack of SLMed high-strength aluminum alloys. The research progress in microstructure and mechanical property control of SLMed high-strength aluminum alloys in recent years was reviewed. The mechanical properties of alloys with different compositions were summarized. Importantly, the main strategies to suppress hot-crack formation in SLMed high-strength aluminum alloys were highlighted, including optimization of SLM process parameters and grain refinement by microalloying or addition of nanoparticles. It was pointed out that the main issue of SLMed high-strength aluminum alloys was the change of alloy composition on the comprehensive properties and heat treatment process was still unclear. The development trends were forecasted, such as designing new high-strength aluminum alloys and evaluating their comprehensive performances, using post-treatment process and other means to further improve the comprehensive performances of the alloys, and designing special grain refiners for SLM and investigating refinement mechanism.

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.

Zr is one of the most deeply investigated and widely used microalloying elements. The low diffusivity of Zr and the formation of thermal-stable Al₃Zr dispersoids with the properties of low density, high melting temperature and low interface misfit in Al matrix, making Zr owing a broad prospect of application in developing heat-resistant Al alloys. However, strengthening by Al₃Zr has been limited by either low number density or low volume fraction. In addition, the interaction among multiple components is very complex in multi-component Al alloys during solidification, deformation and heat treatment, and it is very difficult to achieve a good combination in strengthening of Al₃Zr with the intrinsic phase of each system. In this review, the existing form, the precipitation and coarsening behavior, and the strengthening mechanism of Zr element in Zr-containing Al alloys were summarized. The mechanism of complex microalloying with multiple elements on promoting Al₃Zr dispersion was briefly introduced. Finally, the effects of Zr addition on several series of Al-based alloys were summarized. In sum, microalloying with Zr is of great significance for regulating microstructure and improving room temperature/high temperature strength in Al alloys.

Cobalt (Co) based oxygen reduction catalysts have become one of the important choices to replace platinum based oxygen reduction catalysts because of their low price, high reserves and easy availability. ECP600 JD was pretreated with nitric acid, mixed with cobalt acetate tetrahydrate, and then pyrolyzed at 800 ℃ in ammonia atmosphere to prepare Co-N/C oxygen reduction catalyst. The infrared spectrum test, alkali neutralization titration and specific surface area measurement show that the number of oxygen-containing functional groups on the surface of ECP600 JD increases, the pore size of ECP600 JD remains unchanged, but the proportion of mesopores increases after nitric acid acidification pretreatment. XRD and TEM tests show that Co_5.47N is formed from ECP600 JD and cobalt acetate tetrahydrate after ammonia heat treatment, the Co-N/C catalyst is dispersed evenly without agglomeration. Electrochemical tests show that after pretreatment, the electrocatalytic performance of the prepared Co-N/C catalyst for oxygen reduction reaction (ORR) is better. Under alkaline conditions, the current density reaches 4.2 times that before pretreatment, and belongs to four electron transfer in catalytic kinetics.

One-staged forming of porous C/C composites as well as volume fraction control of pores were realized, based on thermophysical property analysis and proportioning design of raw materials. Short fiber reinforced C/C-SiC composites with high densification and low content of residual Si were prepared by hot-pressing-infiltration two-step method at low temperature. The structural evolution of C/C-SiC composites was analyzed in detail, the mechanical properties as well as failure behaviors were also investigated. Results show that the porous C/C composites present bipolar distribution in pore size, adding aramid fibers is an effective method to improve the connectivity of network pores, exhibiting a significant regulatory effect. Both SiC network skeleton and pinning structure with strong interface between SiC matrix and carbon fiber bundle can entrust the excellent mechanical properties of C/C-SiC composites with high carbon fiber content. In addition, the fracture toughness of C/C-SiC composites can be improved significantly with the addition of aramid fibers, resulting in the increase of crack propagation path. The isotropic distribution of carbon fiber in plane and the uniform distribution of ceramic phase between layers play a positive role in improving the bearing capacity and friction stability of C/C-SiC composites.

Stress corrosion cracking (SCC), as an important research direction in the interdisciplinary of material mechanics and corrosion electrochemistry, is one of the main failure modes of stainless steel components. Compared with traditional wrought technology, additive manufacturing (AM) 316L stainless steel has complicated microstructure and inherent defects including pores and lack of fusion places (LOF) caused by additive manufacturing process, resulting in more complex SCC behavior. Herein, the basic SCC behavior of 316L stainless steel was discussed in detail on the basis of the researches of AM316L stainless steel at home and abroad. The main contents include two stress corrosion mechanisms of hydrogen induced cracking and anodic dissolution. Two behavior of transgranular cracking and intergranular cracking were described. The effects of microstructure on SCC behavior of AM316L, including twins, different crystal interface, pores, LOF, and element segregation were summarized. The current situation and advantages of three in-situ characterization methods, including electrochemical noise, high-resolution neutron diffraction and three-dimensional morphology characterization were introduced, which are of great significance to explore the SCC behavior of AM316L. Finally, the prospective future of the research directions of SCC behavior of additive manufacturing stainless steel were proposed, including the research of SCC characteristics under high temperature irradiation environment and the principle of stress distribution and restructuration at crack tips.

Since the 1960s, aluminum matrix composites have been being investigated globally, and series of high-performance aluminum matrix composites, namely, damage tolerance, corrosion resistance, high-strength, heat resistance and low-thermal expansion aluminum matrix composites, have been developed. These composites have been used in the fields of aviation, aerospace, electronics and transportation. However, the present market for the application of high-performance aluminum matrix composites is still small, as compared to conventional metal materials and polymer matrix composites. In this paper, the advancements in reinforcements, aluminum matrix, processing methods, microstructure, properties and applications for high-performance aluminum matrix composites were reviewed. The problems existing in raw material, engineering, quality stability, property data, cost, application and materials development were discussed. Future directions from the aspects of applied basic research, materials development, engineering and applications were presented. The future directions for high-performance aluminum matrix composites include increasing the quality of raw materials, improving the stability of processing, lowering the cost, strengthening engineering, expanding applications, exploring the additive manufacturing plus die forging process, and developing new-generation nano reinforced and nano/micro hybrid reinforced aluminum matrix composites.

The defects in friction stir welding (FSW) of aluminum alloy, e.g., tunnel defect, lack of penetration (LOP) and kissing bond, are with complex shape and narrow gap by inappropriate welding parameters. Firstly, the characteristics of FSW welding and typical defects were briefly described, and the difficult points in ultrasonic testing were summarized from the low time resolution, incomplete characterization of irregular defects, close acoustic impedance between kissing bond and Al alloy and the reduction of detection sensitivity. Subsequently, the research work on the ultrasonic testing for FSW of aluminum alloy were reviewed from the following four aspects, including conventional ultrasonic testing, time-of-flight diffraction (TOFD), phased array ultrasonic testing and other ultrasonic testing techniques. Finally, the research on the ultrasonic signal processing methods and machine learning methods was prospected. The signal characteristics were analyzed and extracted to further improve the resolution and signal-to-noise ratio of ultrasonic testing and realize the accurate identification and quantification for complex shape defects and subtle defects.

High-entropy alloys have attracted great attention in various fields due to their high-entropy effect, severe lattice distortion, slow diffusion and special and excellent material performance due to the combination of various alloying elements in equal or near-equal molar proportions. Its high strength and hardness, fatigue resistance, excellent corrosion resistance, radiation resistance, near-zero thermal expansion coefficient, catalytic response, thermoelectric response and photoelectric conversion make high-entropy alloys have potential applications in many aspects. High-throughput computation and machine learning technology have rapidly become powerful tools to explore the huge composition space of high-entropy alloys and comprehensively predict material properties. The basic concepts of high-throughput computing and machine learning were introduced in this paper as well as the advantages of first-principles calculation, thermodynamic/kinetic calculation and machine learning in the research of high-entropy alloys. The application research status of high-entropy alloy composition screening, phase and microstructure calculations and performance prediction were summarized. In the final part, the existing problems, and the solutions and future prospects of this field were summarized, including developing tools for first-principles calculations and machine learning of high-entropy alloys, building high-quality databases for high-entropy alloys and integrating high-throughput computing with machine learning to globally optimize the mechanical property and service performance of high-entropy alloys.

In order to prepare a high-bandwidth absorbing material with both mechanical properties and electromagnetic absorption properties, a nano-particle modification and physical blending method were used to design and prepare a carbonyl iron room temperature vulcanized silicone rubber composite material based on polydimethylsiloxane. The mechanical properties and wave absorbing properties of the composite material were systematically analyzed. The results show that when the mass fraction of white carbon black is 3%, the composite material has the best comprehensive mechanical properties and is convenient for material processing; the composite material is a magnetic loss type wave absorbing material, and the attenuation constant of the material is positively correlated with the carbonyl iron content and frequency. According to simulation calculations, the absorption peak of electromagnetic waves gradually shifts to low frequency as the thickness of the composite material and the content of carbonyl iron are increased at 2-18 GHz. When the thickness of the composite material is 1.5 mm and the mass fraction of carbonyl iron is 75%, the effective absorption bandwidth of the absorbing material can reach 9.07 GHz, accounting for 56.68% of the target bandwidth. In practical applications, the formula can be optimized and the thickness of the material can be controlled according to the needs of the application scenario to achieve the best absorbing effect.

MXene has a wide application prospect in energy storage, electromagnetic interference shielding, catalysis, medicine and other fields due to its unique layered structure, high electronic conductivity and rich surface chemical properties.Ti₃C₂T_x, as the earliest discovered MXene material, has the possibility to achieve both high energy density and power density in the field of sodium ion batteries because of its inherent metal conductive characteristics, wide layer spacing and abundant surface functional groups, which is attracted by many researchers. Based on this, the research progress of Ti₃C₂T_x based materials in sodium ion batteries in recent years was reviewed in this paper. Firstly, the structure and electrochemical properties of Ti₃C₂T_x materials with multi-layer and few-layer were summarized by introducing the preparation of Ti₃C₂T_x. Then, combined with the application trend of the study, the influences of layer spacing modification, doping modification and morphology regulation on the sodium storage behavior of the two kinds of Ti₃C₂T_x materials were summarized. The structural design ideas of the two kinds of Ti₃C₂T_x based composites applied to the anode of the sodium ion battery were also analyzed. It was pointed out that the reasonable structural design is vital to the battery performance. Finally, some suggestions for the problems and challenges faced by Ti₃C₂T_x based composites in the field of sodium ion batteries were given.

C_f/SiC composites are considered as one of the most important candidates for aerospace thermal protection systems because of their low density, high specific strength, good thermal shock, oxidation and ablation resistance, and excellent high temperature strength retention. However, C_f/SiC composites are prone to oxidize at a temperature above 500 ℃ due to inevitable fabrication defects. So it is necessary to carry out effective oxidation protection for the composites. Oxidation resistant coating is an efficient technology to realize long-term oxidation protection. Based on harsh requirement of thermal protection systems, the research progress of anti-oxidation coatings for C_f/SiC composites was summarized, mainly focusing on the coating material systems and their preparation technologies. Improving the service temperature (≥1800 ℃) and bonding strength of the coatings is an important issue to be solved at present.The preparation of multi-functional coating with longer service time and higher service temperature, as well as oxidation resistance, water vapor corrosion resistance and even good heat insulation performance is an important direction for future development.

Metal foam composite is a kind of lightweight composite with low density, high strength, high shielding performance, high damping performance and other characteristics. It has a wide range of application prospects in aerospace, drilling trap floats, artificial bone and other fields, which has attracted people's attention. In this paper, based on the research of the existing literature, the fabrication methods of metal foam composites were introduced, the effect of microstructure on the properties of metal foam composites was analyzed, the progress of mechanical properties, damping properties, shielding properties and heat insulation and their mechanisms of metal foam composites and their applications in relevant fields were reviewed, which provides a theoretical basis for the development of metal foam composites in the future, and the new fabrication technology, modeling research, sandwich structure of metal foam composites and the fabrication of high performance foam hollow sphere composite were also prospected.

Melt growth ceramics (MGC) is a new type of ceramic material with microstructure obtained by melting and solidification of raw materials. The clean and high-strength bonding interface shared by atoms makes it have excellent high-temperature mechanical properties and microstructure stability close to the melting point. It shows great application potential in the field of high thrust weight ratio aero-engine and heavy gas turbine hot end components in the future. Laser directed energy deposition (LDED) technology can effectively overcome the limitations of traditional preparation methods of MGC in terms of cycle, energy consumption and structural complexity. It provides a new solution for direct additive manufacturing of MGC components, and has become a research hotspot at home and abroad. Based on the introduction of the process principle of LDED technology, the microstructure characteristics and properties of different MGCs prepared by this technology at home and abroad were summarized in this paper, and the main research on the control of microstructure and cracking behaviour was comprehensively discussed. Based on the existing research progress, the development trend and key scientific problems to be further solved in this field were discussed. It was pointed out that inhibiting cracking and improving microstructure and properties are the primary problems faced at present. The development of materials and new processes is the key to breaking through the existing bottleneck and promote the development and application of MGC-LDED.

SiC ceramics has been extensively used in heat exchangers because of their excellent mechanical properties, high thermal conductivity, and superior thermal shock, corrosion, and oxidation resistance. However, there is a wide variation in the thermal conductivity of SiC ceramics, depending on the raw materials, molding process, sintering process, and sintering additives. The thermal conductivity of SiC ceramics (≤ 270 W·m^-1·K^-1) is much lower than that of 6H-SiC single crystals (490 W·m^-1·K^-1) because of pores, grain boundaries, impurities, and defects in SiC ceramics. In this work, the important factors affecting the thermal conductivity of SiC ceramics were analyzed, including temperature, pore, crystal structure, and second phase. Further, the preparation processes of high conductivity SiC ceramics were systematically compared based on hot-pressed sintering, spark plasma sintering, pressureless sintering, recrystallization sintering, and reaction sintering. The improvement measures of thermal conductivity of SiC ceramics were summarized, including the optimization of the type and content of sintering aids, high-temperature annealing, and adding a high-thermal-conductivity second phase. Finally, the prospects and research directions of low-cost and high-thermal-conductivity SiC ceramics are proposed.

To improve the interface compatibility, dielectric properties and energy storage density of polyimide(PI)-based composite materials, the core@dual-shell nanoparticles, BT@TiO₂@PDA were obtained via facile solution method using the dopamine to coat on the BT@TiO₂ nanoparticles, which is barium titanate (BT) coated with amorphous-TiO₂, hydrolyzed from tetra-n-butyl titanate (TBT). A series of modified BaTiO₃/PI (BT@TiO₂@PDA/PI) composites with different contents of BT@TiO₂@PDA were prepared through a solution casting film formation method. The results show that the dispersion of nanofillers in the polymer matrix and the interface compatibility between them can be improved by utilizing core@dual-shell nano-structured BaTiO₃. The permittivity κ of BT@TiO₂@PDA/PI composite films with 40%(mass fraction) filler loading increase to 8.8 (1 kHz), which is about 2.7 times higher than that of pristine polyimide, 1.4 times higher than that of pristine BaTiO₃/PI composite films. Temperature-dependent and frequency-dependent dielectric performance tests confirm that BT@TiO₂@PDA/PI composites possess good temperature and frequency stability. In the frequency range of 100 kHz, the dielectric loss of the composites is less than 0.010; when the filler loadings are under 40%, the permittivity of the composites decreases by less than 0.6 (1 kHz) from 25 ℃ to 160 ℃.

The additive friction stir deposition (AFSD) technology is a new solid-state additive manufacturing technology. The metal bars, powders, and wires are used as feedstock. During the additive process, the friction heat generated by the friction between feedstock and the plate and the plastic deformation heat generated by the severe deformation of feedstock form a viscoplastic deposition layer. The deposition layer is stacked layer by layer to form three-dimensional parts. Because of its solid phase characteristics, it has many advantages over fused-based metal additive technologies and has become a research hotspot in the field of additive manufacturing. In this paper, the latest research progress of AFSD technology at home and abroad was reviewed from four aspects of equipment development, microstructure evolution, material flow characteristics and mechanical properties change. The feasibility of the application of this technology in engineering practice was analyzed and the application prospect in the field of metal coating reinforcement for material repair parts of additive manufacturing was forecasted. Finally, it was pointed out that the heat generation mechanism, material flow characteristics, auxiliary optimization process, and intelligent equipment development are the future research directions.

The effect of carbon nanotubes (CNTs) on the aging behavior of Mg-9Al matrix composites was studied, and the evolution of microstructures, mechanical properties and thermal conductivity of composites during the aging treatment were discussed. Results show that the addition of CNTs increases the solid solubility of Al in Mg matrix and limited the migration of grain boundaries during the aging process, which can promote the formation of continuous precipitated phases β-Mg₁₇Al₁₂ in CNTs/Mg-9Al composites. The rod-shaped continuous precipitates in coherent relationship with Mg matrix can effectively hinder the dislocation movement, which can improve the mechanical properties of the composites. Besides, the reduction of solid solution Al atoms during aging process and the addition of CNTs can improve the thermal conductivity of the composites. The property evaluation indicates that the tensile yield strength, ultimate tensile strength, diffusivity and thermal conductivity of peak-aged 0.4CNTs/Mg-9Al composite are 275 MPa, 369 MPa, 34.5 mm²/s and 68.4 W/(m·K) respectively, showing 17%, 23%, 43% and 45% increasing in comparison with those of Mg-9Al before aging.

Fuel cell, which directly enables the generation of electricity from the conversion of the fuel through an electrochemical reaction at the electrode and electrolyte interface, without going through the heat engine process, is an incredibly powerful renewable energy technology. The electrochemical reaction in fuel cell is not restricted by the Carnot cycle, so it has high energy conversion efficiency. Proton exchange membrane fuel cell (PEMFC), in particular, has been regarded as the most promising candidate for transportations, portable equipment and fixed devices.However, there are still some problems in PEMFC, including high cost, insufficient power and poor stability, which limit the large-scale commercial application of PEMFC. The basic reason behind these problems lies in the key materials, such as cathode catalyst, gas diffusion layer, proton exchange membrane and bipolar plate in fuel cell, which can not meet the requirements of PEMFC commercialization owing to their high cost and low performance. Therefore, in order to achieve large-scale application of PEMFC, advanced cathode catalysts, gas diffusion layers, proton exchange membranes and bipolar plates are needed. For the requirement of low-cost and high-performance advanced materials for PEMFC, the research status of these key materials and main challenges in their practical application were summarized in the review, and the future development direction was pointed out: developing the technology of large-scale preparation of platinum alloy and metal-nitrogen-carbon (M-N-C) compound catalysts, preparation of proton exchange membranes with high proton conductivity and excellent mechanical property, studying the influence of modified gas diffusion layer on PEMFC performance under different working conditions, developing coatings or new metal materials with excellent corrosion resistance and electrical conductivity for bipolar plates.