Since 1990s, carbon nanotube reinforced metal matrix composites have been received great attention, but have not yet been transferred into commercial applications. Up to now, powder metallurgy has become the main process for preparing this kind of metal matrix composite. By ball milling, extrusion, rolling or sever plastic deformation process, etc., combing with coating on the surface of carbon nanotubes or in-situ carbon nanotubes, the dispersion of carbon nanotubes in the matrix and the interfacial bonding may be improved remarkably. At present, the high-performance metal matrix composites including 0.5% –7.5% volume fraction carbon nanotubes can be prepared. In this paper, the advances in the preparing process, microstructure and properties for carbon nanotube reinforced metal matrix composites are summarized, the potential applications, challenges and future directions are discussed.

With the development of aerospace technology, the performance requirements for key components have been gradually increasing. And single material components are no longer able to meet the performance demands under harsh operating conditions. Therefore, direct near-net shaping of dissimilar metal materials has become a key research direction in aerospace, defense, and military industries. Currently, conventional methods for preparing dissimilar metal materials still face challenges such as processing technique and material property compatibility, interface defect control, and difficulties in achieving integrated shaping. The use of additive manufacturing technology for the fabrication of dissimilar metal components has emerged as an important direction of development in the field of material forming and additive manufacturing. The research status of directed energy deposition, selective laser melting and electron beam melting in the additive manufacturing of dissimilar metals is presented in this paper. An overview and summary are provided with powder deposition processes, compatibility between high energy beam and powder layers, control of fully miscible alloy precipitation phases, joining of immiscible materials using high energy beam, and control of interface composition direction. Additionally, potential solutions to these challenges are proposed. Finally, the future development direction of dissimilar metal additive manufacturing in the aerospace field are prospected.

TA7 ELI (extra low interstitial) high pressure pump shell was prepared by powder metallurgy nearnet shaping technology under the hot isostatic pressing parameters of 930 ℃/120 MPa/3 h. The effects of different batches of powder on the properties of TA7 ELI alloy were compared (surface morphology of the powder was cellular in shape, and their D₅₀ values are 67 μm and 74 μm), and the powder shrinkage law of high pressure pump was studied using finite element method. The cutting of the formed high pressure pump shell was performed for dimensional analysis and microstructure observation. The results show that the mechanical properties of TA7 ELI alloy prepared by powder metallurgy is comparable to the properties of wrought alloy. The particle size deviation of two batches of powder shows no significant influence on tensile properties, the microstructure of high pressure pump shell is homogeneous, the hardness value of the characteristic section fluctuates little, and the maximum deviation between the measured results and the predicted results of the key dimensions of the flow channel inside the shell is 5.37%.

In this study, a microstructure control strategy by combining powder high-energy ball milling, spark  plasma sintering and hot extrusion was proposed. The influence of preparation process parameters on the evolution of grain size, second phase particles and twins was investigated. A CoCrFeNiMnTi_0.2 high entropy alloy with multi-scale heterogeneous microstructure containing coarse grains, fine grains and nanoparticles, and a CoCrFeNiMnTi_0.2 high entropy alloy consisting of ultrafine grains, nanoparticles and nano-twins were prepared. The tensile mechanical properties showed that the yield strength and elongation to fracture of the high entropy alloys were up to 1298 MPa and 13%, and 1507 MPa and 7%, respectively, achieving a good trade-off between strength and plasticity. Lastly, based on the revision of the Holpage coefficient, a strengthening model for nanoparticle reinforced ultrafine grain CoCrFeNi-based high entropy alloy was established. A new coupling mechanism between nanoparticles and heterogeneous structure, as well as a synergetic mechanism of ultrafine grains, nanoparticles and nano-twins were discussed. It was also found that nano-twins could increase the flow stress of high entropy alloy, resulting in multi-level deformation behavior by inducing nucleation of new deformation twins.

In response to the demand for high-temperature resistant porous metal sweating cooling materials for hypersonic weapon engines，the study focuses on nickel based high-temperature alloys. Through comprehensive control of powder particle size selection, forming, and sintering processes, a porous sweating material with uniform pore structure was prepared, and its performance was analyzed. The results show that the maximum pore size of the prepared porous sweating material is less than 21.3 μm. Tensile strength greater than 225 MPa, porosity greater than 25%; By controlling powder particle size, pressing, and sintering processes, effective control of the permeability of sweating cooling materials can be achieved within the range of 10^–13–10^–12 m²; Analyze and characterize the tensile data and fracture morphology of porous sweating materials, and confirm that their fracture mode is ductile fracture.

Porous Inconel 625 alloy products were prepared by a combination of the binder jetting and powder sintering technology. The effect of sintering temperature on the porosity, pore characteristics, microstructure, sintering neck, and tensile properties of porous samples were studied. Firstly, the binder jetting technology is used to prepare green parts, followed by debinding and pressureless sintering to obtain porous specimens. Metallography and fracture morphology were observed through optical microscopy and scanning electron microscopy respectively to characterize and analyze pore characteristics, microstructure and sintering behavior, and the porosity and mechanical properties were characterized by Archimedes drainage method and tensile test respectively. The experimental results show that when the sintering temperature increases from 1150 ℃ to 1280 ℃, the porosity of the sintered product decreases from 24.8% to 8.63%, and the tensile strength increases from 316 MPa to 515 MPa. The best comprehensive performance can be obtained when sintered at 1250 ℃, with a porosity of 17.16% and a tensile strength of 451 MPa. This method provides a new approach for the preparation of porous materials and provides a reference for the influence of sintering temperature on pore structure and mechanical properties of Inconel 625 porous materials formed by binder jetting.

BNi-2 braze was used to brazing C/C composite panel and GH3536 superalloy honeycomb under the brazing parameter at brazing temperature of 1040 ℃ and holding time 15 min. The influence of the thickness of brazing braze on the microstructure and flatwise tensile strength of C/C composite and superalloy honeycomb sandwich structure was analyzed. Results show that the panel-honeycomb interface can be divided into reaction zone between C/C composite and braze, reaction zone between braze and honeycomb and braze solidification zone. Cr₃C₂ reaction layer is formed between braze and C/C composite. Intermetallic compounds of Si are formed within the reaction zone between braze and honeycomb. With the increase of thickness braze, flatwise tensile strength increases first and then decreases. When the braze thickness is 0.12 mm, flatwise tensile strength reaches the maximum level at 9.69 MPa. The fracture site mainly occurs in the C/C composite base material.

In this paper, stainless steel coatings with different NbC contents were prepared on the surface of EA1T axle steel using laser cladding technology. The phase structure and microstructure evolution of the composite coatings were analysed using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), and the hardness and tribological properties of the coatings were determined. The results show that the addition of NbC plays a role in grain refinement, while Fe (Nb, C) type hard phases are precipitated between the grains. However, the addition of NbC resulted in the disruption of the directionality of the dendrites in the coating, but the coating properties were enhanced and increased with the addition of NbC. In particular, when the mass fraction of NbC is 20%, all of the added NbC melts and then precipitates islands of hard phase between the grains. The hardness and wear resistance of the coating is significantly improved by the fine grain strengthening and diffusion strengthening caused by the NbC addition. The addition of 20% NbC increased the hardness by 15% compared to the uncoated NbC, reaching a maximum hardness of 60HRC; The wear coefficient was significantly reduced to 0.75, with the best reinforcement effect. The wear surface plough furrows of the composite coating with 20% NbC were shallow, and the wear mechanism was abrasive wear.

The tool wear not only affects the surface quality and machining accuracy of the workpiece, but also frequent tool change will reduce the machining efficiency and increase the production cost. Studying the mechanism of tool wear, the factors of affecting the tool wear and the modeling technology of tool wear prediction, can provide technical support for reducing the tool wear. The research progress of tool wear and its prediction modeling technology in cutting process was reviewed. Firstly, based on the research progress of tool wear mechanism in recent years, the manifestations and characteristics of several main tool wear mechanisms were analyzed respectively. Secondly, the influence of cutting parameters, tool geometric parameters, tool and workpiece material properties and processing methods on tool wear in the cutting process were discussed, and the modeling method and form of tool wear prediction were summarized and analyzed. Finally, combined with the development concept of green energy-saving in manufacturing industry and the computer technology of high-speed development, the future development direction for the machining methods to reduce tool wear and tool wear prediction modeling technology were pointed out.

The milling processing technology is one of the key technologies in machining parts with the thin wall and complex surface in aerospace. This method can ensure high precision, high-quality and high-efficiency, etc. As one of the important phenomena in milling processing, cutting force directly affects the tool wear, deformation, the processing efficiency and quality of workpiece, and so on. In order to make better use of cutting technology, it is necessary to review and analyze the prediction of cutting forces. As one key method to predict cutting forces, experiencebased milling force models are widely used. Therefore, this paper summarizes the state of art in predicting cutting forces using experience-based models and then analyzes the effect of cutting force coefficient, uncut chip thickness, tool runout, and deformation on cutting force. In order to provide useful reference, the future research direction of this field is finally discussed.