To improve the comprehensive mechanical properties of selective laser melting （SLM） TA15 alloy， the microstructure and mechanical properties of SLM TA15 alloy are studied under annealing conditions of 800 ℃+air cooling， 950 ℃+air cooling， and 1050 ℃+air cooling. The microstructure characteristics of TA15 alloy under annealing conditions are characterized by electron backscatter diffraction. The results show that the orientation and texture of the α phase are not changed after the heat treatment at 800 ℃ or 950 ℃， showing the characteristics of a net basket structure. After the heat treatment at 1050 ℃， the texture with the maximum strength of 9.18 appears along the direction ［0001］， showing the characteristic of the weistenite structure. With the increase of annealing temperature： the width of both α' and α phase increases gradually； the aspect ratio of both α' and α phase increases first and then decreases； the geometrically necessary dislocation density of both α' and α phase decreases gradually； the Vickers hardness of the sample decreases first and then increases， with the highest Vickers hardness of （397.2±10）HV for the unheat treated sample； the strength of TA15 sample decreases gradually； and the elongation increases first and then decreases. After tensile tests， the unheat treated samples show mixed fracture characteristics， the samples treated at 800 ℃ and 900 ℃ show plastic fracture characteristics， and the sample treated at 1050 ℃ show brittle fracture characteristics.

As a common additive manufacturing （AM） technology， selective laser melting （SLM） is a great potential manufacturing technology for special-shaped parts，such as porous and thin-walled parts. However， the traditional single beam SLM technology develops slowly due to the problems of lesser forming size and inferior efficiency. On the basis of single-beam SLM， multi-beam selective laser melting （MB-SLM） uses multiple beams and multiple galvanometers to partition scan and perform overlap forming. It greatly improves the forming size and efficiency， perfectly solves the inherent problems of single-beam SLM，and is expected to become an emerging technology to expand the application of metal additive manufacturing. The research progress of multi-beam selective laser melting in forming principle， forming equipment， and formation and control of defects is reviewed. The microstructures and mechanical properties of different alloys manufactured by multi-beam selective laser melting are summarized. Importantly， the main strategies to control defects and mechanical properties are highlighted. Finally， the development trends are forecasted， such as the impact of temporal and spatial difference characteristics between multi-beam on mechanical properties， and the consistency change of process parameters between different regions to reduce defects of formed parts.

As-deposited parts of 2024 aluminum alloy are fabricated by cold metal transfer and pulse （CMT+P） hybrid wire arc additive manufacturing. The distributions of pore defects， grain morphology， and secondary phase precipitation of CMT+P wire arc additive manufacturing 2024 aluminum alloy， and the influence of different process parameters on pore defects， grain morphology and secondary phase precipitation， and corrosion resistance are investigated. The results show that the pores of the as-deposited parts of 2024 aluminum alloy are mainly distributed near the fusion line. In the same heat input， the larger wire feed speed and travel speed result in higher porosity. In a deposition layer， the upper part is the equiaxed grain without preferred orientation， and the lower part is the columnar grain with preferred orientation. In the same heat input， the texture is weakened and the percentage of equiaxed grains is increased due to the fine grain region in the higher wire feed speed and travel speed. The precipitated secondary phases are mainly Al₂CuMg， Al₂Cu， and rich-Fe， Mn phases. The secondary phases distribute continuously along the grain boundaries. In the early stage of corrosion， the main factor affecting the corrosion resistance of as-deposited parts is the precipitation amount of Al₂CuMg. The better local corrosion resistance is mainly caused by lower Al₂CuMg phase fraction in lower wire feed speed and travel speed.

The effects of different heat treatment processes on the anisotropy of TB6 titanium alloy fabricated by laser deposition manufacturing were investigated.The evolution of microstructure was analyzed by using optical microscope （OM）， scanning electron microscope （SEM）， and transmission electron microscope （TEM）. The variation trend and influence mechanism of anisotropy with heat treatment were investigated. The present research shows that the original β grains and the morphology of the primary α phase （α_p phase） are greatly affected by the thermal gradient. The original β grains in the microstructure of TB6 titanium alloy fabricated by laser deposition manufacturing are elongated along the deposition direction and are ellipsoidal. In addition， the relative slender α_p phase parallel to the deposition direction is found. These two factors jointly lead to the anisotropy of room temperature tensile property of the as-deposited samples. The tensile strength in the vertical deposition direction （X-direction ） is 7.3% higher， the yield strength is 5% higher， and the elongation is 32.4% lower than that in the deposition direction （Z-direction）. The low-temperature annealing treatment has little effect on microstructure， only the anisotropy of plasticity is decreased. After high-temperature annealing treatment， the difference in aspect ratio of α_p phase is significantly reduced， leading to the anisotropy of the room temperature tensile property decreases. The strength are still higher in the X-direction， and the elongation is higher in the Z-direction. The strengthening mechanism of the solution-aging treating sample is completely changed due to the precipitation of the secondary α phase （α_s phase）. In addition， there is no obvious preferential growth of α_s phase after heat treatment， so the anisotropy of the room temperature tensile property tends to be eliminated as the strength increases.

3D printing， as a new manufacturing technology， has been widely applied in the forming and manufacturing of various materials with enormous development prospects. Graphite has excellent high-temperature resistance， conductivity， thermal conductivity， thermal stability， and chemical stability， widely used in fields such as metallurgy， energy industry， aerospace， and nuclear industry. Using graphite and its composite materials as the matrix and 3D printing technology to produce graphite products can reduce the graphite production cycle， improve material utilization， reduce graphite dust pollution， and provide an efficient and economical comprehensive solution for personalized customization and industrial application of high-performance and complex shaped graphite. This article focuses on the 3D printing technology of graphite and its composite materials， analyzes and discusses the advantages and disadvantages of each technology， introduces the performance and application of graphite products formed by 3D printing， discusses the opportunities and challenges of graphite and its composite materials in the development process of 3D printing， and puts forward expectations and prospects for this. The development of graphite 3D printing technology needs to develop the types of expansion of graphite composite materials and new printing equipment and its supporting equipment， and conduct 3D printed graphite post -processing technology based on traditional graphite process.

The selective laser melted （SLM） GH4169 superalloy has a significant directional columnar dendritic solidification microstructure， which can cause severe mechanical property anisotropy and increase service risk. The GH4169 superalloy prepared by laser selective melting （SLM） technology is taken as the research object， and two different heat treatment processes are designed： hot isostatic pressing+standard solid solution+double aging and hot isostatic pressing+homogenization heat treatment+standard solid solution+double aging for post-heat treatment of the prepared alloy. The effect of two heat treatment processes on the anisotropy of microstructure and high-temperature tensile properties of GH4169 superalloy prepared by laser selective melting is investigated. The results show that the homogenization heat treatment eliminates the Laves phase， and the columnar crystal structure of the as-built GH4169 alloy transforms into an equiaxed crystal structure. The high-temperature tensile results show that the high-temperature tensile strength ratio and plasticity ratio of GH4169 alloy in the transverse and longitudinal directions without homogenization treatment are 1.10（1145/1040） and 0.83（10.2/12.2）， respectively. The high-temperature tensile strength ratio and plasticity ratio of GH4169 alloy in the transverse and longitudinal directions after homogenization heat treatment are 1.00（1041/1038） and 1.00（8.6/8.6）， respectively. The anisotropy of microstructure and mechanical properties of GH4169 alloy prepared by laser selective melting is eliminated.

The development of advanced aero-engines with high thrust-to-weight ratios in the future has an urgent need for new high-performance lightweight high-temperature compressor blisks. Laser additive manufacturing TC25G-TiAl4822 gradient structure material is an important material system for the blisk of the lightweight high-temperature compressor. The composition selection and solidification structure research of gradient transition layer alloy have a key influence on guiding the structural performance design of related components. To understand the solidification structure evolution behavior of （1-x）TC25G-xTiAl4822 transition layer alloy with the change of TiAl4822 pre-alloyed powder content in powder raw materials， two kinds of single raw material （TC25G or TiAl4822） alloy ingots and alloy ingots with nine kinds of mixed raw materials are prepared by laser melting technology. Material characterization equipment and hardness measurement devices such as optical microscope， scanning electron microscope， XRD， and TEM are used for the study. The research results show that with the increase of the content of TiAl4822 alloy powder in the raw material， the characteristics of solidified grains change to dendrite → equiaxed → dendrite. The microstructure of the alloy at room temperature changes as follows： α_p+α_s+β+α₂→α_p+ α_s+α₂+β/B2 → α+α₂+β/B2 → α₂+B2 → α₂+γ+B2 → α₂+γ. Due to the change of the phase content of different alloy compositions， the Vickers hardness of the matrix first increases and then decreases， the overall hardness value changes in the range of about 450-620HV when the powder proportion is 50%-70%. If the intermediate composition alloy is directly used as the transition layer， the hardness will suddenly change. Therefore， the selection of the transition layer alloy composition should consider the range close to pure TC25G or TiAl4822.The above results provide the basis for the composition selection of bimetallic transition layer alloys to avoid the intermediate proportion of powder content range.

The microstructure control and corrosion resistance of aluminum alloys fabricated by wire and arc additive manufacturing（WAAM） are important issues that must be studied in engineering applications. The 5356 deposited part is produced by a CMT （cold metal transfer） system. The microstructure and hardness are characterized by metallurgical microscope， X-ray diffractometer （XRD）， scanning electron microscope （SEM） and micro-hardness tester， and the corrosion resistance behavior is studied by using electrochemical workstation， slow strain rate stress corrosion testing machine. The results show that the microstructure of 5356 WAAM aluminum alloy is composed of α-Al matrix and β（Al₃Mg₂） phase. The grains in the deposition layer are columnar crystals with an aspect ratio of ≤2， and the β（Al₃Mg₂） phase exists mainly as finely dispersed particles， while the grains in the interface layer are recrystallized equiaxed grains with smaller size， and the β（Al₃Mg₂） phase is predominantly distributed in large discontinuous blocks along the grain boundaries， with fewer fine granular β（Al₃Mg₂） phase within the grains， leading to a reduction in the matrix strengthening effect. The self-corrosion current density of the deposited layer is 23% of that of the interface layer， which may be caused by the content and morphology of β（Al₃Mg₂） phase. The stress corrosion sensitivity index at a slow strain rate of 5356 WAAM aluminum alloy is 0.57， and samples experience fracture and failure at the interface layer in both silicone oil and 3.5%NaCl solution medium. This is attributed to the lower strength at the interface layer matrix and shearing effect played by large intergranular β（Al₃Mg₂） phase in silicone oil inert medium， while the β（Al₃Mg₂） phase dissolves preferentially in the 3.5%NaCl aqueous solution， and intergranular corrosion propagation is accelerated under tensile stress.

Based on the response surface design， the optimal process parameters for single-side friction stir welding（FSW） of 2195 Al-Li alloy sheets are studied. It is found that the higher the rotation speed and the lower the welding speed， the higher the tensile strength of the welded joint. The results show that in the single-side FSW， when the pin length is 2/3 length of the thickness of the plate， the root of the weld appears unwelded defects， the fracture form of the welded joint is between brittle and plastic fracture， and the tensile strength of the joint is poor. Based on the optimum process parameters of single-sided welding， double-sided FSW can overcome the unwelded defects at the root of single-sided welding. Under different tool pressures， when the stirring head speed is 1600 r/min， the feed speed is 150 mm/min， and the pressure is 0.1 mm， the double-sided welding can improve the tensile strength of the welded joint by about 10% and the elongation of the welded joint by 10%. In two-sided FSW， the material flow on the forward side is obvious， and the fracture mode of the welded joint is a plastic fracture. In double-sided welding， the plate is subjected to secondary stirring and heating， resulting in increased softening of the material in the welding area.The microhardness of the double-sided welded joint is further reduced than that of the single-sided welding.

The joining of aluminum/copper dissimilar metals is successfully achieved by ultrasonic-assisted nano-enhanced plasma arc fusion brazing， and a well-formed aluminum/copper lap joint is obtained. The effects of ultrasonic waves and SiO₂ nanoparticles on the macroscopic and microscopic morphology， organizational structure， mechanical properties and conductive properties of lap joints are analyzed and studied by SEM， EDS， XRD， tensile test and conductivity test. The results show that the lap joint is obtained under the coupling action of ultrasonic waves and SiO₂ nanoparticles， and the spreading and wetting effect of liquid aluminum on the copper surface is better， the front side of the weld is well formed， and the joint is mainly composed of intermetallic compound layer region and Al-Cu eutectic region. The thickness of the intermetallic compound layer is reduced obviously，and the mechanical properties of the joint is significantly improved. The relative conductivity of the aluminum/copper joint using SiO₂ nanoparticles and ultrasonic waves is 153.527%IACS， exhibiting improved mechanical properties and electrical conductivity.

To study the static recrystallization behavior of laser additive manufacturing superalloys and their effect on mechanical properties， the solid-solution strengthened nickel-based superalloy GH3536 was investigated.The selective laser melting（SLM）method was used to prepare test blocks and bars， which were subjected to solution treatment at 1175 ℃ for different time. The static recrystallization behavior during heat treatment was investigated by EBSD analysis to explore its influence on the tensile properties. The results show that the as-built state organization is dominated by columnar grain growing along the build direction with 〈001〉 fiber texture. The recrystallization fraction after heating at 1175 ℃ for 1 h is 61.8%. Twinning is the main formation of recrystallization nucleation， and the degree of recrystallization gradually increases with the extension of the heating time. The recrystallization kinetic curve was obtained by fitting the Avirami equation， which matched the experimental results well. Static recrystallization significantly suppresses the anisotropy of the mechanical properties. The change magnitude of mechanical properties is small after the heating times more than 1 h.

Continuous fiber-reinforced resin matrix composites are widely used in aerospace， automotive and marine industries due to their low density and excellent mechanical properties. However， traditional manufacturing processes are expensive and unable to form complex parts due to mold limitations. Additive manufacturing has the advantages of high freedom of design， rapidity， and flexibility，and is considered an important directions for the future production of continuous fiber reinforced composites. At present， the additive manufacturing technology of continuous fiber reinforced composite is still in its infancy. This paper systematically reviews the research status of continuous fiber reinforced resin matrix composite， summarizes the research progress of printing equipment， process and materials， and provides directions for the construction of printing platform and engineering application of continuous fiber reinforced resin matrix composite. The influence of printing process parameters， such as temperature， speed， and layer thickness on printing quality is analyzed， providing a reference for the intelligent additive manufacturing of continuous fiber reinforced composite materials. Meanwhile， the development of the two-dimensional and three-dimensional structural design for continuous fibers for lightweight manufacturing， such as fiber path laying and structural topology optimization is discussed. The research trends of equipment， materials， printing process， and structural design for additive manufacturing of continuous fiber-reinforced composites are summarized and outlooked.

Due to the large temperature gradient in the laser melting deposition process， the coarse primary β columnar grains with preferred orientation are formed along the deposition direction， resulting in significant anisotropy of materials. This study aims to change the morphology of the primary β grains， refine the microstructure and weaken the texture of titanium alloy by adding Cu element in the materials during the process of laser melting deposition. The effects of Cu content on the microstructure and texture of TC4 titanium alloy manufactured by laser melting deposition are studied systematically. The results show that Cu element addition can refine the columnar primary β grains significantly and make the grain size distribution more uniform. The columnar grains are transformed to fully equiaxed grains when 4% Cu （mass fraction， the same as below） is added into the material， and the average size of primary β grains decreases to 385 μm from 1490 μm of TC4 titanium alloy. Basket-weave microstructure composed of α-Ti， β-Ti， and a small amount of Ti₂Cu is obtained inside primary β grains of the samples with Cu addition. The short rod-like Ti₂Cu distributes at the boundary of the α-Ti lath， and its proportion in the microstructure increases with the increase of Cu addition. The average width of α-Ti is 0.44 μm when 8% Cu is added， which is reduced by about 63% compared with 1.18 μm of the sample without Cu addition. When 4% Cu is added， the maximum multiples of uniform distribution（MUD） value of α-Ti pole figure is reduced by about 71% compared with TC4 titanium alloy，which demonstrates that the addition of Cu can significantly reduce the texture strength of titanium alloy manufactured by laser melting deposition.

Single crystal superalloy turbine rotor blade is one of the core hot-end components of the aero-engine， which has a decisive role in the thrust and performance of the aero-engine. Additive manufacturing for repair technology is one of the most challenging tasks in the special machining of aviation equipment. In this paper， the repair processes and their application for single crystal superalloy turbine rotor blades were systematically reviewed. Aiming at the problems of hot cracking defect， the cracking formation mechanism， key influencing factors， and control methods were summarized. In addition， the research progress in microstructure and mechanical properties of single crystal superalloys repaired by additive manufacturing technology are summed up. Furthermore， the prospective developing direction of single crystal superalloy turbine rotor blade repair is indicated. Specific filler material composition design， new process development， and multi-objective collaborative optimization based on deep learning are considered to be important future research directions.

To improve the impact resistance of metal and composite material joint structures， a metal synapse structure was manufactured using metal laser selective melting technology. The structure was co-cured and molded with T300 twill woven carbon fiber-reinforced composite material （CFRP） to form a through-thickness reinforcement joint structure. The impact resistance of the synapse joint structure was verified through Charpy pendulum impact tests. Analysis and optimization of the synapse morphology were conducted based on CFRP damage patterns and impact absorption energy， as well as other influencing factors. Finite element simulations and comparative calculations were performed. The experimental results indicate that the penetration-enhanced joint method can prevent metal stress concentration and carbon fiber cutting caused by drilling holes. The impact absorption energy measures at 68.54 J， with a 216.1% improvement compared to the bolted connections. Increasing the height of the synapses effectively inhibits the composite material impact delamination. The synapse feature size and synapse array density affect internal defects in the composite material. With increasing synapse feature size and synapse array density，the impact absorption energy first increases to a point and then decreases. Finite element simulations based on synapse feature size variations showed that the simulation results deviated from the experimental results by less than 17%， and the damage form is highly consistent.

The novel Ti69NbCrZrX （X=Sn，W，Al，Mo，1%-2%， mass fraction） was used as an interlayer to join TiAl alloy with Ti₂AlNb alloy by pulsed current diffusion welding at 900 ℃/30 min/8 MPa. The post-weld joint microstructure and properties were analyzed by SEM， EDS， EBSD， and room temperature tensile test. The results show that defect-free TiAl/Ti₂AlNb joints can be obtained using Ti69NbCrZrX as the connecting interlayer. The joint interface microstructure is mainly composed of TiAl diffusion affected zone， interlayer diffusion zone， and Ti₂AlNb diffusion affected zone. The TiAl diffusion affected zone structure is composed of white β phase and gray block α₂ phase，the interlayer diffusion zone structure is mainly composed of gray block α₂+ α phase， and white β/B2 phase composition， Ti₂AlNb diffusion affected zone is composed of β/B2 matrix phase with lath and acicular O phase. The average value of room temperature tensile strength of the joint is 642.5 MPa， which reaches 91.57% of the strength of the base material. The fracture mode of the joints is dominated by brittle intergranular fracture， supplemented by brittle transgranular fracture.

Laser melting deposition is more suitable for repairing thin-walled substrates of single crystal alloys compared to argon arc welding and micro plasma arc welding. This article used laser melting deposition technology for additive repair of DD6 single crystal superalloy. The microstructure characteristics of the repaired zone and heat affected zone of the additive repaired joint were analysed by optical microscopy， scanning electron microscopy， and EBSD. And the microhardness distribution and high-temperature tensile properties of the repaired joint were tested. The results indicate that in the heat affected zone adjacent to the repair interface， γ' phase is partially coarsened and dissolved， and the hardness decreases significantly. The microstructure of repaired zone is an oriented columnar crystal structure grown epitaxially， and composed of γ+γ' phase and a small amount of dispersed carbides between dendrites. Many elongated columnar stray grains remain in the repaired zone， mostly distribute near the fusion line. As the height of the repaired zone increases， the dendrite spacing and hardness of the epitaxial growth tissue increases gradually， and the proportion of fine grid γ' phase in the dendrites increases continuously. The tensile strength of the repaired joint at 980 ℃ reaches 102% of the base material， and the yield strength reaches 92% of the base material， but the elongation is relatively poor.

For Ni₃Al-based superalloy IC10 turbine blades， some defects， such as cracks and ablations， would appear after long-term service. To shorten the overhaul period， the turbine blades can be repaired using the brazing technology. In this study， an independently designed Co-based filler alloy （CoCrNi（W，Al，Ti，Mo，Ta）-B） was used to join the IC10 superalloy. The effects of the brazing gap and the brazing time on the joint microstructure and mechanical properties were investigated. The results show that the designed filler alloy has good brazeability at 1220 ℃ for IC10 superalloy. Because of the interreaction and mutual diffusion， the brazing seam is wider than the preset gap. Meanwhile， the matrix of brazing seam is γ＋γ′ dual phase which was similar to the IC10 base material. Because of the boron in the filler alloy， a large number of white borides are formed. The brazing holding time has little influence on the microstructure and strength of the joint， but the brazing seam has significant effect.With the brazing seam wider， the joint strength tested at 1000 ℃ increases gradually. When the brazing seam is set at 0.15 mm， the joint strength is 454 MPa， which is close to that of the IC10 base material. According to the joint fracture morphology， the increase in joint strength is mainly due to the small and diffuse white boride phase in the joint， inducing the tortuous crack propagation path.

The defects on TB6 titanium alloy were repaired using pulsed TIG（tungsten inert gas） additive manufacturing technology， and the effects of process parameters （pulse current and pulse time） and heat treatment on the microstructure and mechanical properties of the repaired TB6 titanium alloy were studied to determine the optimal heat treatment process parameters. The results show that the mechanical properties are relatively better in the as-repaired state when the pulse current is 50 A and the pulse time is 40 ms， with a tensile strength of 1113 MPa and an elongation of 5.26%. These samples are sequentially subjected to solid solution and aging heat treatment. When the samples are solid solution treated for 2 h under different temperatures （740， 760， 780 ℃）， the primary α phase is increasingly dissolved， while the β phase gradually grows and evenly distributes in the matrix. After water quenching， the growth of the β phase is inhibited， and acicular rhombic martensite α'' phase is precipitated in β grains， resulting in a decrease in tensile strength and a remarkable increase in elongation. Under different aging temperatures （500， 520， 540 ℃） for 8 h， the α'' phase continuously grows and gradually transforms to equiaxial grain， and the mechanical properties are greatly improved. The optimal microstructure and mechanical properties are achieved under the conditions of 780 ℃/2 h WC+520 ℃/8 h AC， with a tensile strength of 1119 MPa and an elongation of 7.36%.

The 6061-T6 ultra-thin aluminum alloy with a thickness of 0.5 mm was welded using micro-joint friction stir welding technology. The effects of three kinds of stirring heads with different shaft shoulder morphology on the forming quality， microstructure， mechanical properties， welding thermal cycle， and force process of the 6061-T6 thin-wall butt joint were studied. The flow behavior characteristics of the plastic metal in the three welding cross-sections were analyzed in sequence. The results show that the forming effect of the weld surface is significantly affected by welding heat input. The hardness distribution trend of the joint cross-section formed by three kinds of stirring heads with different shaft shoulder morphology is a “W” shape. The highest hardness values in the center of the nucleation zone and the lowest hardness values in the thermo-mechanical affected zone of the needle-free three-involute diversion groove shaft shoulder welded joint are the highest among the three shaft shoulder welded joints. The mechanical properties of the joint formed by the three-involute guide groove with the needle shaft shoulder are outstanding， and the tensile strength， yield strength， and elongation after fracture are higher than those of the other two. The three tensile fracture forms are mainly ductile fractures. The process parameters of the thermal cycle and force can accurately reflect the changing trend of the welding state. The energy required to maintain the weld metal softening is from the heat generated by friction between the shaft shoulder and the workpiece and the work done by the axial and forward forces of the shaft shoulder. The axial force and forward force changed with the softening degree of the welded metal， playing a dynamic regulating role in the migration of plastic metal in the weld. The shoulder surface has a strong effect on the upper part of the weld， driving the plastic metal migration between the forward side and the backward side. The needle of the stirring head promotes the interaction between the plastic metal and the backing plate， providing a driving force for the flow of the upper and lower parts of the weld metal. The optimal heat generation potential is the combined result of the stirring needle and the involute groove， which work together to form a well-formed weld.

The microstructure evolution of the interface in the simulated heat affected zone （HAZ） of G115 steel was characterized by electron backscatter diffraction （EBSD） and high resolution transmission electron microscopy （HRTEM）. The results show that the size of precipitated M ₂₃C₆ in the fine grain zone is smaller than that in the coarse grain and the critical zone， which is only about 100 nm， and the precipitation strengthening effect is obvious. With the increase in peak temperature， the number of small angle grain boundary increases， hence the grain boundary strengthening effect increases. The highest geometrical dislocation density is 3.19×10¹⁴ m^-2 in the coarse-grained zone. The recovery of the critical dislocation， the pinning of the fine MX precipitates and the appearance of the subgrains make the G115 steel maintain the durable strength for a long time at high-temperature. For the microstructure of the fine grain zone， the increase of welding heat input promotes the transformation of martensitic lath substructure into martensite block substructure， the dislocations are annihilated， the formation of subgrain is inhibited， and the yield strength decreases from 1115 MPa to 947 MPa. When the welding heat input is 14.4 kJ/cm， the microstructure of the fine grain welding heat affected zone has both good strength and toughness.

The SiC/AlSi10Mg composites were fabricated via selective laser melting（SLM）. The phase characteristics， microstructure， anti-corrosion and wear resistance properties of SLM SiC/AlSi10Mg and SLM AlSi10Mg samples were investigated by XRD， SEM， EDS， EBSD， electrochemical test， and friction and wear test. The results show that in the 3.5% （mass fraction） NaCl solution， the corrosion current density of SLM SiC/AlSi10Mg （2.0827 μA/cm²） is lower than that of SLM AlSi10Mg （3.389 μA/cm²）， and the passivation film on the surface of SLM SiC/AlSi10Mg （7.1 nm） is thicker than that of SLM AlSi10Mg （1.9 nm）， indicating the SLM SiC/AlSi10Mg sample has better corrosion resistance than that of SLM AlSi10Mg. The reason can be attributed to that the addition of SiC causes the grain refinement， the increase of high grain boundary， and the interruption of the continuity of Al matrix， leading to the decrease of corrosion rate and the increase of corrosion resistance. In addition， the average microhardness for SLM SiC/AlSi10Mg composites （207.68±16.02）HV_0.2 is twice that of SLM AlSi10Mg alloy （103.58±7.41）HV_0.2， indicating its hardness and wear resistance are improved. Both the wear mechanisms of SLM AlSi10Mg and SiC/AlSi10Mg composites are mainly abrasive wear and oxidation wear.

High-strength aluminum alloy have become one of the most commonly used metal materials for aerospace and automotive application parts due to its high strength， low density， excellent ductility and corrosion resistance. Wire arc additive manufacturing （WAAM） has the ability to rapidly in-situ form and manufacture complex structural parts， and is very suitable for the manufacturing of medium or large high-strength aluminium alloy parts. The current status of high-strength aluminum alloy WAAM processes and equipment， the inherent properties and defects of high-strength aluminum alloy WAAM， and the main performance optimization methods were comprehensively analyzed in this paper. The inherent characteristics of the microstructure and properties as well as the impact of hybrid additive manufacturing technologies on the microstructure and properties were discussed. Opinions are put forward on issues such as metallurgical defects， characteristic performance requirements， the advantages and disadvantages of various optimization processes in WAAM. Development directions such as a comprehensive evaluation system， composition design and wire development， special heat treatment systems and synergy of composite additive manufacturing technology are proposed. Such proposals are expected to provide references for the performance improvement and application promotion of high-strength aluminum alloys manufactured via WAAM.

Laser additive manufacturing （LAM） enables the integrated direct formation of high-performance metallic components with complex geometry. However， the non-uniform distribution of temperature gradients， in-situ heat treatment effects， non-equilibrium solid phase transformations， and heterogeneous microstructure during the process result in intricate residual stresses that significantly affect the quality and overall performance. A comprehensive review of residual stress in LAM by introducing its fundamental definition and classification is provided in this paper. Furthermore， the particularity， formation mechanisms， characterization methods， and regulation techniques associated with residual stress in LAM is systematically reviewed. The subsequent sections introduce various characterization methods for residual stress in LAM components， along with their respective characteristics. Additionally， the applicability， advantages， and disadvantages of each method are presented. Furthermore， the methods for controlling residual stress can be categorized into post-treatment control and in-situ treatment control. Finally， the joint effect of different types of residual stress should be considered in the study of the cause and evolution mechanism of residual stress in LAM. The characterization method of residual stress should be integrated with various methods to facilitate mutual verification. To mitigate the impact of stress concentration on the printing process and resultant quality， as well as minimize the influence of post-processing stress on part accuracy， it is imperative to investigate in-situ control methods for residual stress and explore real-time online monitoring techniques for LAM.

Refractory high entropy alloys have excellent high temperature mechanical properties， but the high temperature oxidation resistance has always been one of the limiting factors in their application. Four kinds of refractory high entropy alloys AlNbTaTiZr， AlMoNbTiZr， AlMoNbTaTiZr and AlMo_0.5NbTa_0.5TiZr were designed and prepared by laser additive manufacturing technology. The oxidation mass gain of AlNbTiZr-based refractory high entropy alloys was measured at 900 ℃ and 1000 ℃， and the oxidation layer structure of different samples was studied. The effects of Mo and Ta on the high temperature oxidation resistance of AlNbTiZr-based refractory high entropy alloys were compared and analyzed. The results show that the four kinds of as-deposited high entropy alloys prepared by laser additive manufacturing are BCC＋HCP dual-phase structures. The dendrites are mainly BCC phases with high melting points， and a small amount of HCP phase rich in Al and Zr is distributed among the dendrites. AlNbTaTiZr shows the best oxidation resistance after oxidation at 900 ℃ and 1000 ℃ for a long time， and Ta instead of Mo to some extent improves the oxidation resistance of refractory high entropy alloys.

Due to the low boiling points of the main constituents of 7075 aluminum alloy and the high surface tension gradient of the molten alloy， combined with the uneven energy distribution of the circular Gaussian （CG） laser beam spot commonly used in directed energy deposition （DED） processes， the forming quality of 7075 aluminum alloy DED specimens is generally poor. This significantly restricts the further application of DED in 7075 aluminum alloy. By regulating the laser mode， it is possible to effectively modify the temperature and flow fields of the melt pool， as well as the corresponding solidification conditions. Thus， the forming quality of laser additive manufacturing specimens and the active control of microstructure are improved. An off-axis parabolic integrating mirror is employed to homogenize the CG laser mode into a circular flat-top （CF） laser mode， which is further tilted to achieve a transversely elliptical flat-top （TE） laser mode. Using these three different laser modes， single-track cladding， single-wall structures， and 7075 aluminum alloy in DED block specimens are prepared. Combined with numerical simulations， the influence laws and underlying mechanisms of the laser modes on the forming quality and solidification structure are revealed. The simulation results indicate that by modulating the laser beam spot from the conventional CG laser mode to the CF and TE laser modes， the uniformity of the heat flux on the surface of the cladding layer is significantly improved， subsequently reducing the temperature gradient of the melt， and increasing the solidification rate. Compared to the CG laser mode， the surface forming quality of single-wall structures and block specimens under the CF and TE laser modes is significantly enhanced. The width variation of the single-wall structures is greatly reduced， and the dimensional accuracy in the horizontal direction of the block specimens is improved. Additionally， the density of the block specimens increases from 95.8% to 97.2% and 97.7%， respectively. In terms of solidification structure， the texture is significantly weakened， the grain size is reduced by approximately 50%， and the number of nano-precipitated η-phase within the grains is also increased.

Wire-arc additive manufacturing is a new type of manufacture using wire as filling material and arc as a heat source， making it easier to manufacture complex-shaped and big-sized parts. The reciprocating and unidirectional process path experiment was conducted. The inclined wall made by unidirectional path has better morphology， less splash， and a smoother surface. The simulation model of AM11 reciprocating and unidirectional manufacturing path was established in finite element software and solved. The simulation results show that the unidirectional path deposition temperature is 267.4 ℃， the deposition thermal stress is 357.4 MPa， the reciprocating path deposition temperature is 307.0 ℃， and the deposition thermal stress is 420.4 MPa， the heat accumulation and thermal stress of unidirectional path are lower than that of reciprocating path. AM11， AM12， and AM21 inclined wall samples with different slope factors by wire-arc additive manufacturing in unidirectional path were prepared， and their microstructure and properties were analyzed. The results indicate that the grain size of AM11， AM12， and AM21 is 35， 39 μm， and 42 μm， there is more precipitated β-Mg₁₇Al₁₂ in AM21 thin-walled grains， which has larger and more dimples than that of the other two samples. The micro-hardness values of AM21 and AM11 are both about 81.5HV， higher than 73.1HV of AM12. The horizontal and vertical tensile strengths of the AM21 inclined wall sample are 255.7，224.4MPa， the yield strengths are 103.8，96.0 MPa， and the elongations reach 13.1% and 8.2%. The tensile strengths and elongations are both greater than those of AM11 and AM12 samples， but the yield strengths are close. The AM21 inclined wall has much better strength and plasticity， and verify that the more perpendicular the inclined wall of magnesium alloy arc additive manufacturing is， the better the mechanical properties such as strength and plasticity.

The stereolithography 3D printing technology provides a new technical solution for the preparation of complex structure SiC ceramic parts， but the characteristics of high light absorption and high refractive index of SiC lead to a common problem that printing is difficult to cure. SiO₂ with low absorbance and low refractive index was added to SiC ceramic matrix powder as filler to improve the curing property and printing accuracy of SiC ceramic paste. The effects of different amounts of SiO₂ on the rheology， stability and curing properties of the slurry and its mechanism were studied. The green body with high precision and good surface quality was prepared by stereolithography 3D printing technology， and the microstructure and properties of the green body were tested and analyzed. The results show that the adding SiO₂ to the SiC slurry can reduce the viscosity， improve the stability， and improve the curing property of the slurry. The addition of SiO₂ can significantly improve the surface roughness of the SiC green body and make the bending strength increase at first and decrease then.

To improve the quality of laser cladding， a finite element analysis process was established， focusing on laser power， scanning speed and powder feed rate as the main process parameters， aiming to reduce the research and development cycle and economic costs of optimizing cladding process parameters. By comparing the temperature and stress field simulation of GX4CrNi13-4 martensitic stainless steel laser cladding data with experimental results， the forming quality under different parameters is verified， optimizing the laser cladding process parameters. The results indicate that the adjustment range of laser power should be controlled between 1800 W to 2000 W to avoid substrate penetration and ensure sufficient density； increasing the powder feed rate effectively reduces temperature and residual stress. Among the three process parameters， laser power has the most significant impact on cladding quality. A comprehensive analysis of density and microhardness tests to assess the cladding quality and residual stress distribution under different parameters reveals that the optimal combination of process parameters is a laser power of 1800 W， scanning speed of 10 mm/s， powder feed rate of 10 g/min. The experimental results are consistent with the trends of stress field simulations， further validating the accuracy of the simulation data.

High-quality thick Ti-6321 titanium alloy welded joints were obtained by tungsten inert gas（TIG）welding， the microstructure changes of fusion zone， heat affected zone and base metal zone of the welded joints before and after annealing were compared.The impact properties， fracture toughness and tensile properties were tested， and which were compared with the base metal. The results show that the microstructure of the fusion zone before annealing is composed of coarse β columnar grains with fully grown intragranular acicular martensite α′ phase， and heat affected zone consists of equiaxed structure with β matrix and primary α phase， martensite α′ phase precipitates in β matrix.After annealing， the martensite α′ phase in β matrix of the fusion zone and heat affected zone completely transforms into secondary α phase. The impact toughness， fracture toughness， tensile strength and elongation of Ti-6321 titanium alloy welded joints are 80.3 J/cm²， 113.00 MPa·m^1/2， 873 MPa and 9%， respectively， which are 104.7%， 84.1%， 100% and 67.7% of the base metal，respectively. Compared with the fracture of the base metal， the impact fracture of welded joints has a coarser stepped surface and smaller equiaxed dimples， while the fracture surface of toughness is more flat and the fatigue crack propagation zone is narrower.

Oxide eutectic ceramics have excellent high specific strength, high temperature resistance, corrosion resistance, oxidation and creep resistance, and so on, which are considered to be the promising materials to be used in ultra-high temperature oxidation, corrosion and other extreme environments. It shows great application prospects in the new generation of high thrust-to-weight ratio aero-engine for high-temperature hot-end structural components. Laser additive manufacturing technology has become one of the most promising cutting-edge technologies for the preparation of high-performance complex structural components in recent years. Crack defect is easy to occur in the process of laser rapid solidification of ceramics, which seriously affects the quality and performance of the oxide eutectic ceramics components. So, it has become a key factor restricting the engineering application. Two typical laser additive manufacturing technologies for ceramics including laser engineered net shaping and laser power bed fusion were briefly summarized. The crack morphology characteristics of different shaped components formed by the above two technologies were analyzed and compared. The formation mechanism of cracks in laser additive manufacturing of oxide ceramics was explored from the perspectives of microstructure characteristics, stress state. Further, a systematic summary was presented focusing on the improvement of microstructures and the reduction of thermal stress to inhibit crack formation through optimization of process parameters, compositional design, and outfield assistance. Finally, it is pointed out that the future development trends and breakthrough directions of oxide eutectic ceramics by laser additive manufacturing in terms of powder properties, forming primary and secondary factors, and forming technology research.

Ti-6Al-4V alloy is widely used in aerospace and chemical equipment manufacturing due to its good strength, plasticity, toughness, corrosion resistance and weldability, but its hardness and abrasion resistance are not high enough to limit its service life under frictional wear conditions to some extent. Ti-6Al-4V alloy homogeneous cermet cladding layer with TiC-added phase was additively prepared based on the optimized process method of laser cladding, and the strengthening effect of TiC enhancement with respect to the cladding layer microstructure as well as the basic mechanical properties was characterized and verified. The results show that the main phases of the cladding layer include α-Ti, β-Ti and TiC, of which TiC is supersaturated and precipitated within the cladding layer. Due to the difference in the supercooling degree at different locations of the cladding layer, the precipitated TiC is mainly in the form of fine particles at the top of the cladding layer, while it is mainly in the form of dendrites and petals in the middle of the cladding layer. The bottom of the cladding has a new wheat spikes precipitation shape, while no significant TiC precipitation is seen in the dilution zone. The average microhardness of the cladding layer is 530HV_0.5, which is 61% higher than that of the substrate; the average friction coefficient of the cladding layer is 0.3583 at 35 N load, which is 11% lower than that of the substrate, and the volume wear rate is about 87% that of the substrate, and the wear is in the form of adhesive wear and abrasive wear.

The TiC/IN625 coatings were prepared on 45 steel substrates by using extreme-high-speed laser cladding(EHLA) technology. The effect of different heat treatment temperatures(800, 1000 ℃ and 1200 ℃) on the microstructure, surface morphology, residual stress and corrosion resistance of TiC/IN625 coatings was analyzed. The results show that the coating segregation phenomenon is alleviated with the increase of heat treatment temperature. The distribution of Ti elements in the HT1000 coating is more uniform than that in the HT0 and HT800 coatings. The part Laves phase in the HT0 coatings starts to dissolve in the HT1000 coatings, releasing Nb elements that recombine with C and Ti elements to generate MC (M=Nb, Ti) carbides. The large-sized carbides in the microstructure of HT1200 coatings surface dissolve. The other elements, such as Ti and Ni, more homogeneously distribute and diffuse into the inter-dendritic region. The residual stress on the HT0 coatings surface is mostly expressed as residual tensile stress, with a maximum value of 362 MPa. The electrochemical corrosion tests indicate that the open-circuit potential is increased from －0.139 V for the HT0 coatings to －0.132 V for the HT1200 coatings. The charge transfer resistance (R_ct) of HT800, HT1000 and HT1200 coatings is also larger than that of the HT0 coatings, with an increase of 46.2%, 31.2% and 64.3% compared to the HT0 coating's 4.785×10⁵ Ω∙cm², respectively.

The forming technology of surface micropattern structure was widely used in practical manufacturing as a means to texture the surface of materials and to promote advanced and functional materials. The main methods of surface micropattern forming include hot embossing, chemical etching, electrical discharge machining(EDM), photolithography and 3D printing depending on the application areas of materials. The different surface micropattern structure forming techniques and the basic principles of preparing surface texturise functional materials were reviewed, and their practical applications in photovoltaics, electronic information, intelligent manufacturing, ultra-precision manufacturing and other fields were listed. The characteristics and scope of application of different surface micropattern structure forming technologies are summarized, and the key problems faced in realizing the surface texturisation and functionalization of materials are put forward, which provides certain reference for the micromachining technology of surface micropattern structures.

In order to expand the application of polypropylene (PP) in 3D printing technology and improve its mechanical properties, PP/polyethylene terephthalate (PET) blend filaments were prepared by extruding PP with PET using melt blending. The rheological behavior, crystallization structure, melting and crystallization behavior, microstructure, mechanical properties of the filament blends and 3D printed samples with different mixing ratios of PP, PET were analyzed. The results show that the viscosity of PP/PET blends decreases with the increase of shear rate and exhibits shear thinning behavior. PET acts as a nucleating agent and does not change the crystal shape of PP during PP crystallization. The melting temperature of PP is about 150 ℃, and the crystallization temperature increases with the increase of PET concentrations. The PP matrix and PET dispersed phase have obvious "sea-island" structure, in which PET is the "island" phase, with a diameter of 2-5 μm. With the increase of PET concentrations, the tensile strength of filament blends is improved. Simultaneously, the tensile strength and the impact strength of the 3D printed samples is improved. However, the mechanical properties of 3D printed samples are generally lower than those of filament blends due to interlayer interaction.

TCGH(TC4+GH4169)composite material was prepared by selective laser melting(SLM). The optimum forming process parameters of TCGH composite material were investigated, and the microstructure and mechanical properties of as-deposited samples and heat-treated samples were studied. The results show that the optimum process parameters for fabrication of TCGH composite material are scanning speed of 900 mm/s with laser power of 150 W, and density higher than 99.5%. The addition of GH4169 powder changes the solid phase transformation behavior of TC4 titanium alloy material, and the as-deposited structure shows obvious high temperature solidification characteristics, which makes the forming characteristics of progressive scanning overlap and layer-by-layer scanning accumulation obvious. The original coarse columnar β grain size along the printing direction is significantly reduced, and the tensile strength of the composite is improved. Compared with the as-deposited sample, the microstructure of the heat-treated sample is transformed into a near-equiaxed structure. At the same time, with the increase of heat treatment temperature, the dissolution of the second phase leads to the dominant solid solution strengthening effect of the composite material, which improves the tensile strength and plasticity of the composite material.

An experimental study on high cycle fatigue behavior of selective laser melting (SLM) TC4 alloy was carried out. The fatigue properties of the alloy under two sampling directions (horizontal and vertical) and two temperatures (room temperature and 400 ℃) were compared and analyzed. Also the feasibility of improving the fatigue properties of the alloy by hot isostatic pressing (HIP) was explored. The results show that the fatigue properties of the alloy after annealing are significantly anisotropic, and the fatigue properties of the vertical samples are higher than that of the horizontal ones. Compared with room temperature, the fatigue life of the alloy at 400 ℃ is reduced, but the anisotropy still exists. After hot isostatic pressing, the fatigue life of the alloy presents a certain degree of improvement, and the anisotropy of fatigue properties decreases. The fracture analysis shows that the cracks of SLM TC4 alloy mainly originate from surface and subsurface defects which are mainly pores. The statistical analysis shows that the source defect size of vertical samples is lower than that of horizontal samples, which is the main reason for the decrease of fatigue properties of horizontal samples. After hot isostatic pressing, cracks in both horizontal and vertical samples of the alloy are generated at the surface slip, and the porosity of the alloy is significantly reduced without obvious defects, and the decrease in the number of defects is the main reason for the improvement of fatigue properties of the alloy.

In order to study and expand the application of Inconel718 alloy in high temperature environment, Co/TiN composite coating was prepared on its surface by laser cladding. Meanwhile, the tribological behavior of the coatings at room temperature (RT) and 600 ℃, and the oxidation resistance at 800 ℃ were investigated by XRD, SEM and EDS analysis, etc. The results show that the hardness of the composite coatings is 1.3-1.4 times higher than that of the substrate. The tribological properties of the coating are tested. When the TiN content is 4%(mass fraction, the same below), the anti-friction properties of the coating are the best. When 6%TiN added, the wear resistance of the coating is the best, and the wear rate can be reduced by 90.02%. In addition, the oxidation experiment shows that the Co/TiN composite coating has a certain oxidation resistance, and the oxidation rate is 8.7634 mg²·cm^-4·h^-1, which is not much different from the substrate.It shows that the composite coating can significantly reduce the wear rate at high temperature while retaining the oxidation resistance of the substrate, and the wear rate decreases with the increase of TiN. The wear mechanism analysis shows that the oxidation wear occurs on all coatings at 600 ℃, and the oxide film on the surface of the coatings also can reduces the wear rate at some extent.