Application features and research status of alternative 3D-printing materials for six typical 3D-printingtechniques were reviewed. From the point of view of physical forms, four kinds of materials of liquid photosensitive resin material, thin sheet material (paper or plastic film) , low melting point filament material and powder material are included. And from the composition point of view, nearly all kinds of materials in the production and life are included such as polymer materials: plastic, resin, wax; metal and alloy materials; ceramic materials. Liquid photosensitive resin material is used for stereo lithigraphy apparatus(SLA); thin sheet materials such as paper or plastic film are used for laminated object manufacturing(LOM); low melting point polymer filament materials such as wax filament, polyolefin resin filament, polyamide filament and ABS filament are used for fused deposition modeling(FDM); very wide variety powder materials including nylon powder, nylon-coated glass powder, polycarbonate powder, polyamide powder, wax powder, metal powder(Re-sintering and infiltration of copper are needed after sintering), wax-coated ceramic powder, wax-coated metal powder and thermosetting resin-coated fine sand are used for selective laser sintering(SLS). Nearly the same above powder materials are used for selective laser melting(SLM), but the printed parts own much more higher density and better mechanical properties. Powder materials are likewise used for threedimensional printing and gluing(3DP), however, the powders are stuck together by tricolor binder sprayed through nozzle and cross-section shape of the part is color-printed on it. Finally, the development direction in both quality and the yield of 3D-printing materials were pointed out to be a bottle-neck issue and a hot topic in the field of 3D-printing.

The AlSi10Mg powder was prepared by supersonic gas atomization. After classified, the powder was fabricated into block by selective laser melting (SLM). The microstructure, phase, and evolutions of powder and block were investigated by optical microscope, scanning electron microscope and X-Ray Diffraction. The tensile properties of SLM block were tested by tensile experiments at room temperature. The results show that the size distribution of AlSi10Mg powder after classified can meet the requirements of SLM technology. The powder always is spherical and spherical-like. Meanwhile, the microstructure of powders is fine and uniform, which contain α(Al) matrix and (α+Si) eutectic. In addition, the melt pool boundaries of SLM block are legible. The microstructure is also uniform and densified, the relative density approaches to 99.5%. On the other hand, only α(Al) and few Silicon phase are detected in this condition, due to the most alloying elements are dissolved in α(Al) matrix. At room temperature, the ultimate tensile strength of SLM block reaches up to 442 MPa.

Solid propellant is an important source of power for rockets and missiles, and its performance improvement is of great significance for improving the combat capability of missile weapons. 3D printing technology as a focus on advanced manufacturing technology, able to complete high-precision, high-complexity device manufacturing that is difficult to achieve by traditional manufacturing processes, solve the problems of uneven mixing, poor product consistency, and low safety, which are difficult to solve by traditional solid propellant pouring process, has broad prospects in the field of solid propellant manufacture.. The slow progress of the research on the preparation of solid propellant by 3D printing is mainly due to the two major problems of safety and process bottleneck. In view of the safety issues of solid propellant 3D printing, solid propellant 3D printing and related work are divided into three stages: 3D printing of partial energetic components, 3D printing of mixed propellants, and 3D printing of solid propellants. The safe printability of energetic components should be demonstrated step by step. In review of the bottleneck problem of solid propellant 3D printing process, the development progress of 3D printing propellant special slurry and equipment is introduced. From the current achievements and development, the future research on solid propellant 3D printing should focus on the development of special formulation and the realization of large-scale printing.

The friction extrusion additive manufacturing (FEAM) process of aluminum 6061-T651 cylindrical bar was successfully achieved by using independently developed solid-state friction extrusion additive equipment. The forming characteristics, microstructure features and mechanical properties of the final specimen obtained under different rotational speeds were comparatively analysed and discussed. The results show that for a given transverse movement speed of 300 mm/min, a fully dense single-channel double-layer specimen with thickness of 2 mm and 4 mm without any internal defects can be obtained by using the rotational speed of 600 r/min and 800 r/min respectively. The final specimen achieved under the higher rotational speed presents a flat interface, a narrower deposition layer, and a rougher surface because the effects of friction and extrusion experienced by the rotational shoulder are weakened during the deposition process. The plastic deformation and thermal cycle experienced by the bonding interface under 600 r/min are more significant than those under 800 r/min, and the grains are refined to 6.0 μm. The softening degree of the interface obtained under 600 r/min is more serious, and the hardness in this region is only 52.7%-56.2% of the value of the as-received feed rod, while this value can reach 56.0%-61.3% of the hardness of the base material. The final specimen attains a good comprehensive mechanical property. The ultimate tensile strength of the final specimen obtained under rotational speeds of 600 and 800 r/min can reach 66% and 70% of the value of the as-received feed rod respectively, while the percentage elongation after the break can reach 212% and 169% of the value of the base material respectively. The tensile properties of 6061 aluminum alloy prepared in this paper have obvious advantages compared with those of other Al-Mg-Si alloys fabricated by other well-developed additive manufacturing processes.

Based on the traditional manufacturing technology, the “classic” structure, which has a large mass and many weak parts of fatigue is difficult to satisfy the development needs of future fighter aircraft. The innovative structures ( three-dimensional bearing overall structure, bionic structure, gradient metal structure and micro truss lattice structure) based on the advantages of additive manufacturing technology characteristics, breaking through the shackles of traditional structures, with lightweight, long-life, low-cost and other characteristics, can greatly improve the quality of the body platform, providing an effective technical way for the future development of new fighter aircraft. Taking the fuel pipe joint, ring radiators and three-dimensional frame beam integral structure as examples, this paper expounded the whole process of integrated development of new additive structure design and manufacturing, and compared with the original traditional manufacturing scheme, achieved significant benefits, such as substantial weight loss, improvement of finished product rate, and reduction of fatigue weak parts. In addition, the reference significance of cross-domain technologies such as fiber optic sensing and construction structure to the innovation of aircraft structure was also discussed.

In recent years, as the 3D printing technology growing maturity and commercialization, the researchers have attempted to apply this emerging manufacturing technology to the design and fabrication of wave-absorbing materials. In this paper, the recent progress of 3D printing technology in fabrication of microwave absorbing materials, including 3D printing FSS and metamaterial absorbing materials, 3D printing honeycomb absorbing materials, 3D printing ceramics and other 3D printing microwave absorbing materials are reviewed. Furthermore, the limitations of 3D printing materials, the lack of mechanical properties of materials, the problems of testing and analysis of microstructure of 3D printing technology in microwave absorption materials manufacturing are also systematically expounded, at the same time, the future developing trend of 3D printing technology in the manufacturing field of microwave absorption materials, such as miniaturization, multi-function and intelligent is also prospected.

As the most representative additive manufacturing method in the field of aviation equipment at present, the laser additive manufacturing supports the structure design innovation, rapid development and verification. Among them, selective laser melting is mainly used for precision near net shape manufacturing of complex precise functional structures, and laser direct metal deposition is mainly used for manufacturing large and complex load-bearing structures. In order to support the strategic layout of the development of additive manufacturing technology in the aviation field, this paper sorts the current situation and development trend of laser additive manufacturing, and points out that the focus of additive manufacturing development is bound to turn to the metallurgical quality, mechanical properties and their stability control of products. The research and development of intelligent functions such as online monitoring, parameter self-tuning control of additive manufacturing equipment are becoming a research hotspot. Either the research on mechanical behavior of additive parts based on damage failure analysis and life prediction or the performance evaluation and verification technology based on components and characteristic structures have begun to attract the attention of engineering application departments. Based on the analysis of the technology development trend, the development goal of laser additive manufacturing technology in the aviation field in 2035 and the corresponding policy and environmental support and guarantee needs are proposed, and the technical development roadmap in 2035 is put forward. In 2025-2035, the control technology of microstructure, property and deformation for additive manufacturing of ordinary metal, intermetalliccompound, Nb-Si and ceramic based material is to be made a comprehensive breakthrough, the performance verification is to be basically completed, the functional assessment has been partially completed, and some products are to be entered mass production. Important load-bearing structures of aircraft and rotating parts of aeroengine made by additive manufacturing are to be widely used.

Wire arc additive manufacturing (WAAM) is an additive manufacturing technology with high deposition rate that produces a variety of high-performance metal structures layer by layer stacking. The research on WAAM technology of large and medium complex aluminum alloy and titanium alloy for aviation equipments has been widely concerned. In this paper, the WAAM technical definition, classification, forming system and principle are discussed. The recent research progress in the microstructure properties, metallurgical defects, quality improvement and technical application of typical components of aluminum alloy and titanium alloy formed by WAAM in aerospace field both at home and abroad is reviewed. The key common problems in the WAAM forming large and medium complex components of aviation equipments are analyzed, and the 2035 WAAM forming technology route planning map is proposed. In 2035, the "shape control" and "property control" technology of WAAM aluminum alloy and titanium alloy component is to be mastered; the large and medium complex structure components of aluminum alloy and titanium alloy which formed by WAAM are achieved comprehensive application in aviation equipment.

Additive manufacturing technology has a broad development prospect in the field of aviation equipments. As an important metal additive manufacturing process, the electron beam additive manufacturing is in a rapid development stage. The wire-feed electron beam additive manufacturing can meet the requirements of rapid and low-cost manufacturing of aviation large size structural parts and can be used to repair high-value damaged parts. Electron beam selective melting has obvious advantages in the manufacturing of complex structures and refractory alloy parts. Based on the analysis of the state-of-arts of the electron beam additive manufacturing technology, the roadmap of the electron beam additive manufacturing for aviation equipments in 2035 is comprehensively analyzed and drawn from the five aspects of development needs, objectives, common key technologies, applications, strategic support and guarantee in order to provide reference for the development of the electron beam additive manufacturing technology of aviation equipments. In 2035, a perfect additive manufacturing standard system is to be built; and electron beam additive manufactured key load bearing components for airplane andaeroengine realize mass production and application.

Laser additive repair technology is suitable to repair the metal parts of military aircraft. It is an important thrust to prolong the flight service life and improve the ability of independent maintenance. This paper introduced the characteristics of laser additive repair technologies such as selective laser melting forming, laser direct deposition forming, laser cladding and laser arc composite additive manufacturing. The common types of defects with different scales, such as edge collapse, surface spheroidization, porosity and crack in the process of laser additive repair were described, and the corresponding control methods were proposed. The laser energy density, overlap ratio, feeding speed of filler materials, shielding gas flow, time parameters and scanning path of laser additive repair technology were summarized, and the repair performance was improved by the application of external energy field and optimization design of special filler materials. Finally, the application of laser additive repair technology in the maintenance of aircraft wing beams, turbine blades, single crystal blades, landing gear and other metal parts was listed. The future research trend of laser additive repair technology in auxiliary system design, multi energy field fusion, evaluation standard formulation was emphasized, the research and development of mobile laser additive repair equipment were discussed.

IIn order to improve the corrosion resistance of 300M steel surface, NCLT was used in cw-1k solid-state Nd: YAG laser system, Hastelloy C276 coating with 800W laser power and 8 mm/s scanning speed was prepared on the surface of cw-1k solid-state Nd: YAG laser system. The macro morphology, microstructure, phase composition, microhardness, friction and wear properties and electrochemical properties of C276 coating were tested. The results show that the microhardness of C276 coating is increased by 1.4 compared with the substrate. However, the wear resistance of the coating is lower than that of the 300M steel substrate, the corrosion potential of the coating is the highest, the self - corrosion current density is the smallest. The C276 coating is prepared on the surface of 300M steel by laser cladding technology, which significantly improves the corrosion resistance of 300M steel surface, and provides a new scheme for improving the corrosion resistance and corrosion resistance of the material surface.

Turbine blades of long-life civil aircraft and gas turbines are affected by high temperature oxidation during service, which greatly reduces the surface strength under complex working conditions and significantly shortens the service life. Therefore, oxidation resistance is one of the most specific properties that must be considered in the application of turbine blades. The influence of the different drilling processes for cooling holes on the oxidation behavior of Ni-based SX (single-crystal) superalloy at 980℃ and 1100 ℃ was investigated. The difference in the oxidation mechanism of the cooling holes under different drilling processes provided a basis for the establishment of the blade life model under service conditions. The results indicate that the film cooling holes processed by millisecond laser exhibit poor oxidation performance, and all oxidation kinetic curves basically obey the parabolic or linear law. In the initial oxidation stage of the millisecond laser specimen, the oxidation reaction is primarily determined by the growth pattern of outer NiO. Subsequently, a three-layer oxide layer（(Ni, Co)O-Spinel phase layer-α-Al₂O₃） gradually formed around the hole. There are relatively micro-holes under the internal α-Al₂O₃ layer and the γ'-free zone, which makes the oxide layer easy to exfoliate. Discontinuous α-Al₂O₃ is rapidly formed in the initial oxidation stage of the picosecond laser specimen, and then connected to each other to form the dense α-Al₂O₃ layer.

According to the repair demand of aircraft 30CrMnSiA high-strength steel pull rod, the laser cladding process research and pull rod repair were carried out using gas atomized 30CrMnSiA powder as cladding material. The effects of different process parameters on forming quality were compared. The microstructure, mechanical properties and wear resistance of the cladding area under the optimal laser process were studied, and the damaged part of the pull rod was repaired by this process and dimensional measurement was carried out. The results show that using the optimal laser cladding process, the cladding layer with good metallurgical bonding with the base metal and dense microstructure can be obtained. The cladding layer is composed of columnar or honeycomb shaped ferrite and surrounding martensite. The microhardness of the cladding layer is about 475HV, about 36% higher than that of the base metal, and the average tensile strength of the joint is about 9% higher than that of the base metal. Compared with forged 30CrMnSiA steel, the depth of wear track of the cladding layer is reduced by 27.7%, and the width of wear track is also reduced by 35.2%, which means better wear resistance. By using this process, a repaired pull rod with good cladding quality, satisfactory dimensional accuracy and basically no thermal deformation is obtained, so the qualified products are delivered.

In the current aviation industry, laser melting is an ideal technique for repairing and surface treatment of TC4 alloy parts, which has advantages over traditional metal repair techniques in terms of process. In this work, laser melting repair processes were performed on the surface of alloy specimens by different laser scanning speeds at a power of 2 kW, and the changes in metallographic organization, electrochemical corrosion properties and mechanical properties of the repaired surfaces were detected and analyzed. The results show that the significant microstructural changes are occurred during the laser repair process. The best corrosion resistance of the repaired surface is achieved at a laser scanning speed of 150 mm/min. The best microhardness and wear resistance of the repaired surface are achieved at 200 mm/min.

WC is one of the cladding synthetic materials that effectively improve the surface tribological properties of TC4 alloy, but it is easy to produce residues in the coating, which always plagues the quality and performance of the coating. In this study, TC4+WC titanium wear-resistant coatings with different WC addition ratios (5%, 10% and 15% (mass fraction /%)) were prepared on the surface of TC4 by coaxial powder feeding laser cladding technology, and the macrostructure, microhardness and tribological properties of the coating were analyzed and studied, focusing on the melting and residue mechanism of WC in the molten pool. The results show that the addition of WC does not affect the types of phases formed in the coatings. The precipitated phases mainly include in-situ TiC and matrix phases α-Ti and β-Ti. Among them, TiC and the remaining WC particles in the coating form a coherent package mosaic structure phase. The decomposition of WC in the molten pool is prevented, leading to the remaining WC is prone to residue and agglomeration. The amount of WC added is positively correlated with the microhardness of the coating. As the WC content in the material system gradually increases, the wear resistance of the coating gradually increases, and compared with the TC4 substrate, the wear rate of the coating decreases by about 21.1%, 38.2%, and 56.1%, respectively, but the residual WC leads to local stress concentration in the friction and wear process of the coating, the tribological performance fluctuates significantly.

4D printing technology has attracted people's attention since it came up in 2013. 4D printing is a kind of new manufacturing technology which is based on 3D printing and smart materials. In other word, 4D printing is evolved from 3D printing and aimed at the improvement of structure, property and function. 4D printing predicts that the self-assembly, multifunction and self-healing can be achieved. This paper reviews the whole research progress of 4D printing in time sequence, and summarizes the achievements of this technology in material science, manufacturing industry, bioengineering and medical science. In addition, the application perspectives in this field are also discussed.

Additive manufacturing technology (AM) is a new type of manufacturing technology based on the discrete-stacking principle and processing component with computer model data. Selective laser melting (SLM) is an important technology in the field of additive manufacturing. With its integrated manufacturing characteristics and significant advantages in the field of complex structural parts manufacturing, it has become a key development technology and frontier direction in the field of aerospace manufacturing. This article reviews the material system and application fields of SLM technology, and mainly analyzes the latest process research of SLM technology and typical applications in the aerospace field. It focuses on the research progress and results of SLM iron-based alloys, nickel-based alloys, titanium alloys and aluminum alloys. While SLM technology is widely used in various fields, there are also many problems and shortcomings, such as many internal defects of forming materials, cracks and deformations of high-performance materials, lack of standard systems, and low compatibility of powder materials. Constraints require further in-depth work in these areas.

4D printing is a new developing technology that has been developed rapidly in recent years. It is of great significance for the development of intelligent structure of aeronautical and aerospace equipments. This paper discusses the development process and the demand for the multifunctional structure of the fighter, and explains the important functions of 4D printing in the realization of aircraft functions integration, explores the definition of 4D printing, special materials, processing equipment and structure characteristics. The application potential of 4D printing in intelligent variant structure, the new generation of thermal protection technology and the new stealth technology are also discussed. The development proposals of 4D printing in technical maturity, key technical breakthrough and discipline integration are given.

In order to solve the problems existing in airworthiness verification of the large integral metallic structure for civil aircraft main bearing part, the airworthiness verification of the metallic structure additive manufacturing technology was carried out. Through the analysis of applicable airworthiness clauses of additive manufacturing technology, the general idea of airworthiness verification of the metallic structure additive manufacturing technology of civil aircraft is given, including the establishment of material specification, the determination of material strength properties, the selection of structural special factor, and the verification of structural performance. Each verification method gives a specific implementation approach. Taking outer cylinder of the nose landing gear pillar which is made by additive manufacturing technology with A-100 ultrahigh strength steel as an example, a specific implementation plan for airworthiness verification of additive manufacturing technology for large integral metallic structure is given.

The titanium alloy-superalloy dissimilar material composite structure can give full play to the respective advantages of the two materials and achieve complementary performance, which has important application prospects in the field of aeroengine manufacturing. In this paper, the (V-15Cr)+0Cr13 intermediate layer structure was designed for TC4-GH4169 composite structure, and was prepared by laser melting deposition technology. The effects of the laser power and the powder stacking method on the metallurgical quality of the interface of the laser melting deposited TC4-GH4169 dissimilar material were studied. The results show that the interface metallurgical control of the (V-15Cr)+0Cr13 composite interlayer is a key factor affecting the metallurgical quality of TC4-GH4169. For the powder feeding laser melting deposition process, when the laser power is 400 W, there is no effective metallurgical reaction between 0Cr13 and V-15Cr due to the low laser energy, resulting in interlayer peeling; when the laser power is 600 W, a small amount of brittle σ phase appears at the interface of (V-15Cr)/0Cr13; when the laser power is increased to 800 W, there is a greater dilution ratio between the 0Cr13 and V-15Cr cladding layers, and the continuously distributed σ phase with a thickness of about 20 μm is formed at the interface. By using powder presetting laser melting deposition process and focusing the laser on the surface of the V-15Cr layer, the dilution ratio between the 0Cr13 and V-15Cr cladding layers can be controlled at a reasonable level, the formation of the σ phase at the interface can be effectively avoided. The shear test results show that the fracture occurs in the V-15Cr alloy layer. The interfacial strength reaches 299 MPa and the strength coefficient reaches 0.61.

This paper reviews the recent research progress on laser assisted machining technology. On the experimental research aspect, the technical characteristics of various processes including laser assisted turning, milling, drilling, and grinding have been summarized, and the effects of laser and cutting parameters on machining quality have been stated. Investigations show that properly increasing laser power and decreasing cutting speed and feed rate within limits is propitious to fully soften the workpiece material in the cutting zone, and therefore improves the machinability of the workpiece material and enhances the machining efficiency and quality. Current simulation research on laser assisted machining is mainly focused on the cutting temperature field and machining process. By establishing the model of temperature field, the best temperature range for removing workpiece material can be predicted and the cutting parameters can be optimized. Cutting process simulation discusses the influence of physical quantities in machining such as stress, strain, and temperature, providing a basis for controlling the quality of the machined surface in real operations. In the future, the study on machining mechanism, processing techniques and simulation for optimization should be strengthened, and the data base for laser assisted machining processes should be found, in order to promote the industrial application of the technology.

As a novel structural material proposed by topology optimization, metamaterials present unusual properties, such as negative Poisson’s ratio, negative indexofrefraction and so on. Metamaterials have potential application in the aspect of wave controlling and stealth. Therefore, it has aroused great interests in the world. Additive manufacturing technology, also called 3D printing technology, is suitable to make structures with complicated geometries. It is a high geometric freedom to fabricate stealth metamaterials via additive manufacturing technology, which provides technical support for the wide applications. The design of structure and the theory of stealth are both mentioned based on the basic theory of metamaterial. Moreover, a variety of additive manufacturing processes for the preparation of stealth metamaterials, such as light curing method, fusion deposition method, laser selective sintering / melting method are described in detail in the present paper. Problems, for instance, the staircase effect, raw material adhesion, thermal diffusivity, dimensional accuracy and roughness occurred in the fabrication of additive manufacturing metamaterials are discussed in order to provide references for the follow-up researchers.

Sandwich panels with multilayer pyramidal truss cores were manufactured by additive manufacturing. The compressive resistance and destructive behavior were obtained by test under compressive load. The experimental results show that the compressive behavior is very stable, and the load-displacement curves show the same change regulation. The node regions of pyramidal lattice emerge plastic deformation firstly with the increase of compressive load, and then several fractures occur at the node regions of the middle two layers. The average compressive strength of the sandwich panels with multilayer pyramidal truss cores is 6.72 MPa. The molding quality of the back of pyramidal truss is bad owing to the restriction of the technology, so the radius of the truss is smaller than theoretical value. The experimental compressive strength is smaller than theoretical value and simulation calculation value. The compressive strength by theoretical analysis is higher than experimental value because of idealized assumption; while the simulation calculation result agrees with experimental result, the error is around 20%. Comparing the load-displacement curves and deformation, the simulation calculation method will exactly calculate the compressive resistance and destructive behavior of sandwich panels with multilayer pyramidal truss cores.