Titanium and its alloys are widely used in aerospace, automobile and ship, petrochemical industry, biological medicine and other fields because of their low density, high strength, good corrosion resistance and good biocompatibility. The article mainly aims at the preparation technology of powder metallurgy of titanium and titanium alloys, current situation are introduced. Powder manufacturing and densification at home and abroad are introduced. It is pointed out that the key for the future development of powder metallurgy titanium alloys is the preparation of low clearance element fine titanium powder, large size green and high performance sintered preform.

The effect of deformation on the depth of the surface densification layer of powder metallurgical Fe-CuMn-Mo-C materials was investigated using plastic densification techniques. By increasing the amount of deforma‐ tion, the pores on the surface of the parts were reduced and the surface densification depth and hardness were im‐ proved. The experimental results show that the surface of the powder metallurgy parts prepared by extrusion densi‐ fication technique can form a uniform densification layer and the surface hardness of the parts can be improved. When the finished deformation is increased to 0.4 mm and 0.6 mm, a dense layer of about 0.25-0.4 mm is formed on the surface of the powder metallurgical parts with a specimen density of 6.8 and 7.0 g/cm3. The depth and hard‐ ness of the surface dense layer increase with the amount of deformation, indicating that the amount of deformation is one of the most important factors influencing the surface densification effect of the parts.

Cu-Sn powders were prepared by pre-mix and pre-alloy process, the microstructure and phase changes of Cu-Sn alloy were studied after sintering, and the sintering properties of Cu-Sn powders prepared by these two methods were tested and compared. The experimental results show that the microstructure of pre-mixing CuSn10 and CuSn20 is composed of α phase and α + δ eutectic tissue after sintering, while that of pre-alloy CuSn10 is α phase. After sintering, the pre-mixed Cu-Sn green compacts expand, on the contrary the pre-alloyed green com‐ pacts shrinkage. In addition, the strength, oil content and effective oil content of the pre-alloyed Cu-Sn parts are higher than those prepared by the pre-mixing method.

In order to extend the service life of heating surface tubes of a boiler by increasing its wear resistance， the technology of high velocity arc spraying are utilized to prepare wear-resistant coating of Ni55 on the surface of SA-210C. The spray coating was remelted by a tungsten electrode argon arc welding machine and the microscopic structure，phase composition，bonding strength，microhardness and erosion resistance of the substrate and coating was investigated. The results show that the coating crystal is mainly composed of γ-（Fe，Ni）、Ni3Fe、CrB、 Cr7C3、Cr23C6、Fe3B and WC. The coating forms a typical lamellar structure during deposition，which is mainly dominated by mechanical bond and has good compactness. The bonding strength of spray coating is 40.85 Mpa which is prompted to 53.25 MPa after remelting. The average hardness of the spray coating is 1 081HV which was also prompted to 1 143HV after remelting. In the conditions of erosion angle of 45°，erosion velocity of 200 m/s and temperature of 600 ℃，the remelting coating has the best erosion wear resistance，and the spray coating has better erosion wear resistance than substrate metal. The erosion wear behavior of the remelting coating is same as brittle materials. The hard phases like CrB、Cr7C3、Fe3B are combined strongly with coating，which has the function of resisting continuous cutting by abrasive grains. The erosion mechanism is the peeling of the oxide film and the micro-cutting and ploughing of the substrate metal by the abrasive particles.

The selective laser melting forming technology is increasingly used in the manufacture of complex com‐ ponents for aerospace equipment. However, such parts have thin-walled curved features have a large residual stress, which could induce large residual stress and deformation and seriously restrict the forming accuracy and quality. AlSi10Mg is widely used in the production of parts in the field of additive manufacturing due to its low density, high specific strength and good corrosion resistance. In this paper, we analyze the influence of the process parameters and geometric features on the support connection by simulating the laser-selective melting of thinwalled surface features under non-solid support, and study the residual stress distribution and deformation law of the surface features under non-solid support based on this simulation. The thermoplastic method is used to simulate the connection of the non-solid support with different support forming laser power and support structure, and the support parameters are selected with the goal of connection effect. The residual stress and deformation distribution of thin-walled surface features with different wall thicknesses and forming heights are simulated, experimentally verified and discussed based on the intrinsic strain model with the application of the selected support parameters. The simulation results show that the strength of the non-solid support connection is related to the laser power. The decrease of the laser power leads to the decrease of the stress level at the support connection. The stress values at the support connection of each group decrease by14.7%,14.6% and 17.3% respectively with the decrease of the la‐ ser power. When optimizing non-solid support parameters for forming simulation and experiment of thin-walled curved parts, it is found that the peak deformation of thin-walled curved parts increase with the rise of forming height, and the thinner the wall thickness of the parts, the greater the peak deformation. Under the condition of using laser power of 350 W, 3×3 grids and adding independent external contour support, the non-solid support con‐ nection effect of AlSi10Mg is the best, and with the increase of laser power, the support connection is also stronger. The addition of non-entity contour support can effectively improve the support connection. The local deformation of thin-walled curved parts with non-solid support is obviously improved. The residual stress distribution of thinwalled curved parts is mainly affected by the Z-direction normal stress of the parts, and increases with the increase of the thickness of the parts.

The tape casting method is applied to the production of metal films. Due to the large specific gravity of the metal powder and the complicated preparation process of the casting process, the metal film is easily deformed and cracked. In this paper, the influence of the content of various additives in the metal casting slurry on the form‐ ing process and sintering properties of the metal film was studied. The result shows that the binder content and vis‐ cosity have a decisive influence on the performance of the metal film. Adding 10% pore-forming agent can effec‐ tively control the phenomenon of particle agglomeration, membrane pore size distribution is concentrated, the gas transmission rate increases. The influence of solid content on the uniformity of the slab is verified. The solid con‐ tent is too low can cause surface cracking, uneven thickness, many defects and poor strength after sintering. And the solid content is too high, will lead to the film layer gas permeability decline, at the same time, the flexibility of the film layer will also be reduced. Pore forming material can significantly improve the surface agglomeration phe‐ nomenon of membrane layer and improve the binding force between particles.

Titanium alloy has the characteristics of high strength, lightweight, and high temperature resistance, making it a promising aerospace structural material. The traditional mechanical manufacturing process is difficult and costly, which limits the application of titanium alloys. Additive Manufacturing (AM), as an emerging advanced manufacturing technology, can produce metal components with high three-dimensional accuracy through layer by layer machining, providing near net shape machining for titanium alloys. This article first introduces the preparation technology of spherical titanium alloy powder, including Plasma Rotating Electrode Atomization Process (PREP), Electrode Induction Gas Atomization (EIGA), Plasma Atomization (PA), and Plasma Spheroidization (PS). The preparation technology and advantages and disadvantages of four spherical titanium alloy powders are compared, as well as their applications in aviation additive manufacturing, including Laser Selective Melting (SLM). The application characteristics and development trends of different titanium alloy powder preparation technologies in aviation additive manufacturing are summarized, such as Electron Beam Selective Melting (EBSM) and Laser Melting Deposition (LMD). It is pointed out that the key to the future development of spherical titanium alloy additive manufacturing is the preparation of low gap titanium powder. High precision, high efficiency and large scale of additive manufacturing equipment will be the future development trend.

HSS and tool steels perform specially with their high mechanical and thermal properties such as high strength and toughness, high hardness, high wear resistance, and good heat resistance, which are widely used in in‐ dustries such as metalworking, plastic injection molding, and automotive manufacturing, etc. Conventionally, they are prepared by traditional casting and forging process, which always introduce compositional segregation and coarse carbides in their microstructure. These micro defects are difficult to eliminate through conventional process‐ ing methods such as forging, leading to the deterioration in material properties. The powder metallurgy process pro‐ vides an uniform microstructure, fine dispersive carbides, and high alloy composition, which allows for the manu‐ facturing of complex shapes and structures of the final products. Through this approach, the tool and die products have the advantages of higher performance, higher precision, and longer life, and have important applications pros‐ pects in the high-end manufacturing industry. In this work, a comprehensive review of the production technologies and applications of powder metallurgy HSS and tool steels are provided. Besides, the technological innovations in the industrial production, the manufacture methods, and the microstructural properties of powder metallurgy HSS and tool steels are discussed in details. Furthermore, the classifications and applications of these materials, offering an outlook on the future development trends in powder metallurgy HSS and tool steels are summarized.

TA15 titanium alloy samples were prepared by selective laser melting (SLM) forming technology. The effects of heat treatment on microstructure, tensile and impact properties of TA15 titanium alloy samples were stud‐ ied. The results show that under the single heat treatment mode, with the prolongation of holding time and the in‐ crease of annealing temperature, α' martensite in the microstructure gradually decomposes, and the volume fraction of the secondary α phase and β phase gradually increases, and the tensile strength of the samples show a downward trend, but the fracture toughness increases at first and decreases subsequently. Under the heat treatment system of 850 ℃ for 4 h, the sample has better comprehensive properties, its tensile strength is 1 033 MPa, and the impact en‐ ergy is 38 J. Under the double heat treatment mode, the microstructure is mainly a basket-weave structure α+β twophase structure, the degree of microstructure homogenization is higher, which shows that the dispersion of macro‐ scopic properties is smaller, with an average tensile strength of 1 029 MPa and impact energy of 40 J.

The development and application of hot extrusion process for P/M superalloys in Europe and US were summarized. The research progress of hot extrusion process for P/M superalloys in China was described. The selection principles of extrusion process parameters for René 95, René 88DT and FGH4096 alloys were introduced. The influence of extrusion process parameters (extrusion ratio, extrusion speed, extrusion temperature, etc.) on the extrusion forming, microstructure and properties of P/M superalloys was emphatically expounded. The evolution behavior of non-metallic inclusions in P/M superalloys during hot extrusion was clarified.

In this paper, the mechanical properties, microstructures and fracture surfaces of TC4 powder titanium alloy prepared by hot isostatic pressing were compared and analyzed, and the effect of oxygen content on its mechanical properties was studied. The results show that the microstructures of TC4 titanium alloys as hot isostatic pressing and annealing have no obvious difference and are lamellar; the oxygen content increases from 0.11% to 0.17%, the strength and plasticity of titanium alloys increase obviously, and the fracture toughness KIC of TC4 titanium alloys decreases from 101 MPa·m^1/2 to 95 101 MPa·m^1/2; the fracture mechanism of TC4 titanium alloys under room temperature tension is typical microporous aggregation fracture. The mechanism is that cleavage facets appear on the tough section with the increase of oxygen content.

The effect of Y₂O₃ content on the microstructure and mechanical properties of Ti-6Al-4V alloy produced by spark plasma sintering（SPS）using the Ti-6Al-4V＋xY₂O₃（x＝0，0.2%，0.4%，0.6%，0.8%）powders as raw materials was investigated with optical microscopy and TEM. The results show that the grain size will be refined through adding Y₂O₃，when the content of Y₂O₃ exceeds 0.2%，the grain size will increase with the increase of Y₂O₃ content；and the mechanical properties of Ti-6Al-4V alloy can be effectively improved through adding Y₂O₃， when the content of Y₂O₃ equals to 0.2%，the Ti-6Al-4V alloy achieve its best mechanical properties，in which the yield strength，the maximum compressive strength and the compressive strain are 970 MPa，1 852 MPa and 31.4% respectively，and improves by 7.8%，14.1% and 19.4% respectively compared with Ti-6Al-4V alloy without adding Y₂O₃，and its densification increases to 99.28%. The Y₂O₃ mainly improves the mechanical properties of Ti-6Al-4V alloy by increasing the density of Ti-6Al-4V alloy and the pinning effect in the alloy.

Spherical powder for metal 3D printing is generally prepared by the technology of atomization, the met‐ al powder prepared by electrode induction-melting gas atomization (EIGA) without crucible has the advantages of low oxygen increment, high fine powder yield, high sphericity and good fluidity. In this paper, a numerical simula‐ tion of the airflow field at the bottom end of the guide tube of the atomizing nozzle is carried out, and the influence of the length of the guide tube and the atomization pressure on the gas reflux is studied, and the simulation results are verified by the atomization experiment. The results show that there is a critical value for the length of the guide tube. When the length is lower than the critical value, the flow velocity of the gas outside the annular seam of the atomizing nozzle is higher than that inside, and the gas is easy to return to the inside of the guide tube, resulting in more defective powders. When the length is higher than the critical value, the flow velocity of the gas inside the annular seam is higher than that outside, the gas reflux disappears, and the number of defective powders is greatly reduced. The atomization pressure mainly affects the particle size of the powder. The greater the atomization pres‐ sure, the smaller the powder particle size.

The Gibbs free energy, adiabatic temperature and calorific value of AlV85 master alloy prepared by alu‐ minothermal method were calculated according to the thermodynamie prineiples, the process was studied using dif‐ ferential thermal analysis, the kinetic equations of AlV85 alloy produced by the aluminothermal method with differ‐ ent sizes of Al powder were constructed. The reaction of AlV85 master alloy by the aluminothermal method can be carried out and maintained spontaneously，with adiabatic temperature of 2 327 K and calorific value of 4 169 J/mol. Al powder is melted first and reacts with solid V2O5 to replace V and produce part of AlmVn, then part of V and AlmVn react to form V solid solution at about 1 000 K. The particle size of aluminum powder has a great influence on the reaction process and reaction products; The kinetic equations of AlV85 master alloy preparation with differ‐ ent particle sizes aluminum powder is constructed, the smaller the particle size, the lower the activation energy and the higher the frequency factor.

The development of low cobalt or cobalt-free ternary precursor materials is of great significance for the development of low cost and high energy density ternary lithium electric materials. In recent years, due to the longterm high price of cobalt salt, it has become a constraint on the development of new energy vehicles. Among them, medium/high nickel or lithium rich manganese based cathode materials have attracted widespread attention. The electrochemical performance of cathode materials based on lithium batteries largely depends on the performance of precursors. It is particularly important to study the effects of ammonia concentration, pH value, nucleation method, and reaction temperature on surface morphology by preparing low cobalt or cobalt free precursors. The precursor material Ni 0.6Mn0.4(OH)2 was prepared by coprecipitation controlled crystallization method with nickel sulfate and manganese sulfate as raw materials. During the preparation process, the effects of ammonia concentration, pH val‐ ue, nucleation method, and reaction temperature on the morphology of the product were mainly investigated. The effects of ammonia concentration, pH value, nucleation mode and reaction temperature on the surface morphology of the precursor were characterized by SEM and EDS. The effects of different ammonia concentrations on the phys‐ ical and chemical indicators of the material were characterized by carbon sulfur analyzer, tap density tester, and BET. The effect of different ammonia concentrations on the electrochemical performance of positive electrode ma‐ terials was characterized through electrochemical testing. The results show that when the ammonia concentration increases from 0 mol/L to 0.14 mol/L, the primary particles of the precursor grow gradually from filamentation to transverse broadening, and the increase of ammonia concentration is conducive to the preparation of low-sulfur and dispersive precursor. The influence of pH value on the surface morphology of precursors is mainly manifested in the nucleation rate and growth rate of precursors, as well as the degree of primary particle thickness. High pH val‐ ues prioritize nucleation with growth as a secondary factor, while low pH values have the opposite effect. Com‐ pared to the above two influencing factors, the nucleation method mainly affects the sphericity of the precursor and the core structure of the precursor. The nucleation method using nickel cobalt manganese solution, ammonia solu‐ tion, and sodium hydroxide solution simultaneously has poor sphericity, but high capacity and poor circulation. However, the nucleation method using nickel sodium solution simultaneously has high sphericity of the precursor, and good capacity and circulation of the positive electrode material. The reaction temperature mainly affects the thickness and sphericity of the precursor primary particles. The higher the temperature, the thicker the primary par‐ ticles, and the worse the sphericity. Finally, the ammonia concentration is determined to be 0.14 mol/L, with pH ranging from 11.5 to 11.6. The nucleation method uses nickel solution and sodium hydroxide solution simultane‐ ously to prepare precursor Ni0.6Mn0.4(OH)2 with good morphology and excellent electrochemical performance as the cathode material. The results show that the precursor products with excellent performance can be prepared only when the appropriate ammonia concentration matches the appropriate reaction pH value, nucleation method and re‐ action temperature.

Aluminum powder is the most commonly used metal fuel in the explosives and propellants industry. How to make aluminum powder react as completely as possible in explosives and propellants has always been a difficult problem to solve. The combustion-assisted materials and technologies for aluminum powder are systematically reviewed and the different mechanism of promoting the combustion of aluminum powder is analyzed in this paper. Ammonium perchlorate(AP), fluorine-containing materials, nitro-containing compounds, azide-based materials, etc. have significant auxiliary effects on the oxidation of aluminum powder, and the aluminum-containing composites prepared by self-assembly process can help aluminum powder react completely more effectively.

In order to study the high temperature oxidation properties and thermal shock resistance of TiN/Cr-coat‐ ed zirconium alloys, TiN/Cr-coated zirconium alloy samples were prepared by magnetron sputtering. High tempera‐ ture oxidation and thermal shock resistance experiments were carried out respectively, and the microstructure, phase and adhesion strength of the samples after high temperature oxidation and thermal shock resistance were characterized. The results show that there is a clear boundary between the TiN/Cr double-layer coatings prepared by magnetron sputtering, and there are round-like agglomeration protrusions on the surface of the samples, but the coating structure is dense and free of defects such as cracks and pores. After high-temperature oxidation, the sur‐ face Cr coating is partially oxidized to Cr2O3, which is an irregular polyhedral structure. Ti atoms from the TiN coating diffuse to the surface and combine with O to form TiO2, which is a long-striped structure. The Cr2O3 aggrega‐ tion area is bubbling. At the interface between the coating and the substrate, the in-diffused Cr atoms and the outdiffused Zr atoms form a Cr-Zr diffusion layer with a thickness of about 5 μm. At the same time, O atoms continue to diffuse into the sample and combine with Zr atoms to form ZrO2. Although the oxidation weight gain of the TiN/Cr coated zirconium alloy is smaller than that of the uncoated zirconium alloy, and the sample remains relative‐ ly intact, the internal zirconium alloy is oxidized due to the continuous diffusion of O atoms, indicating that the TiN/Cr coating cannot provide good long-term high temperature oxidation resistance for zirconium alloy. After the thermal shock test, the surface coating still completely covers the entire sample, but there is a molten pool-like area on the surface of the sample, accompanied by microcracks and pores, and the adhesion strength of the coating film/ substrate is significantly reduced.

Cu-based friction materials with different lubrication component such as the flake graphite, spherical graphite, coke, artificial graphite, and cryptocrystalline graphite, were prepared by powder metallurgy technology. The tribological and brake performance of Cu-based friction materials with different lubrication component were tested by the MM3000 friction and wear tester. The results show that the average friction coefficient of the Cubased friction material with artificial graphite as lubrication component is the highest (> 0.40), but the wear loss is the largest of all at the speed of 3 000~7 000 r/min. The friction coefficient of the Cu-based friction material with coke is the second (> 0.375), and the wear loss is the smallest of all. The friction coefficient and wear loss of the Cu-based friction material with coke is good than the Cu-based friction material with commonly used flake graph‐ ite. Under the braking condition of 7 000 r/min, the instantaneous friction coefficient of Cu-based friction material with artificial graphite is the highest, and the braking time is short. However, the surface temperature rise of the Cu-based friction material with artificial graphite is the largest. The instantaneous friction coefficient and braking time of the Cu-based friction material with coke is second, but the surface temperature rise of friction material is the smallest. The overall performance of the Cu-based friction material with coke is better than the friction material with flake graphite. Therefore, Cu-based friction materials with coke as lubrication component have better tribolog‐ ical and braking properties, relatively.

High-entropy alloy coatings can bring out the excellent comprehensive performance of high-entropy alloy on the basis of economy and practicality, but its strengthening method is mainly solid solution strengthening, and the strengthening effect has great limitations, so it is necessary to introduce hard particles into high-entropy alloy coatings to achieve composite enhancement, so as to obtain a high-entropy alloy composite coating with better performance. This paper reviews the main techniques for preparing high-entropy alloy composite coatings, such as laser melting technology, plasma melting technology and argon arc melting technology, and focuses on the current research status of direct addition and in-situ synthesis of hard particles to enhance high-entropy alloy composite coatings, analyzes their organization and structure, and discusses the effects of hard particles on high-entropy alloy composite coatings in terms of hardness, wear resistance, corrosion resistance and high-temperature oxidation resistance, respectively. Finally, the problems in the research of high-entropy alloy composite coatings are summarized .

Heavy-duty and special vehicle transmissions generally use friction plates based on copper-based powder metallurgical materials. With the development of the transmission to high speed, high torque, heavy load, etc., the problems of inadequate performance of traditional friction plates are gradually leaking out, such as friction layer peeling, core plate fracture. Aiming at the problems that are becoming increasingly evident in copper-based friction plates, the development process of friction discs and the current application status of copper-based friction discs are analyzed, their composition and material composition are introduced, and the common failure forms and requirements of friction discs are explained. Further, the targeted strategies are proposed in terms of composition design, manufacturing process, structural design, post-treatment strengthening, and so on. It is pointed out that the optimization of multi-process coupling and the resrarch of new environmentally friendly composite friction plates will be an important direction for the development of friction plates.

In this paper，93W-5Ni-2Fe tungsten heavy alloy prepared by powder metallurgy method were tested at 1 000，1 100，1 200，1 300 and 1 400 ℃，the high temperature mechanical properties were investigated respectively. The fracture analysis and the developing principles of fracture mechanism were studied. The results show when the elevating temperature is 1 000- 1 400 ℃ ，mechanical properties of 93W- 5Ni- 2Fe alloy，such as tensile strength，elongation，reduction of area and Young's module get worsedramatically. Material becomes brittle，transgranular fracturecan be hardly found，binder phase tear and inter-facial fracture between tungsten grain and binder phases are domestic fracture mode.

Aluminum alloy with small density，high specific strength properties received extensive attention and application.Composites prepared by powder metallurgy have some advantages：flexible alloy composition design， tiny and homogeneous microstructure. Compared with the composites prepared by ordinary smelting method，the composites with powder metallurgy have more excellent mechanical properties and were used more widely. This paper introduces the internal and overseas research status about powder metallurgy aluminum alloys，the process about the preparation and consolidation of powder and post-processing technology. Meanwhile the characteristics and effects of each process were analyzed，especially several kinds of forming technologies. Otherwise，On the basis of the powder metallurgy，the development of powder metallurgy aluminum alloy-graphene and the development trend of powder metallurgy is briefly introduced.

To form a satisfactory bonding between Molybdenum-Hafnium-Carbon (MHC) and GH4099 alloy，in‐ terlayers are used to alleviate the huge property difference, such as thermal expansion coefficient of the two materi‐ als. This study focused on interlayers and different layer composition to investigate the bonding microstructure and fracture mechanism.Direct diffusion bonding between MHC and GH4099 is difficult due to the low diffusion rate and brittle intermetallic compound formed. Hot isostatic pressing diffusion bonding technology (HIP-DB) was ad‐ opted as the major process in this study by inserting layers between them. The effect of different interlayers (NiCr-Si-B, Ag-Cu-Ti, Ti-Cr-Ni, Nb-Ni ) on the mechanical performance of welded joint between MHC and GH4099 alloys by (HIP-DB) was investigated. Optical Microscope (OM) and Field Emission Scanning Electronic Micro‐ scope (FE-SEM) with energy dispersive spectroscopy (EDS) analysis were applied to analysis the microstructures of the bond, fracture morphology and element distribution. Ni-Cr-B-Si interlayer tends to form brittle Mo-Ni inter‐ metallic phase that is regarded as the main cause of brittle fracture morphology observed. Bond strength with NiCr-B-Si interlayer is very poor. Ag-Cu-Ti interlayer can both react with MHC side and GH4099 side, which lend bond shear strength of 27 MPa. Microstructure observation shows that there are Kirkendall pores reside in the frac‐ ture surface which is responsible for the low bond strength. Ti-Cr-Ni interlayer does not form an effective metallurgical bonding, which is attributed to the intrinsic weak strength of TiCrNi material and low HIP-DB process tem‐ perature. Nb-Ti interlayer forms good metallurgical bonding between MHC and GH4099. Effective diffusion has taken place in MHC/NbTi bond although some pores exist in this area, due to the significant difference of diffusion rate of Mo and Nb. The diffusion-induced reaction layers are determined to be the Mo-Nb solid solution, Ni8Nb, Ni 3Nb and Ni6Nb7. Their strength and thickness are measured in order to establish a correlation between the interfa‐ cial microstructure and joint properties. It is found that the precipitated phase Ni3Nb shows high strength and good plasticity, which is beneficial to the high-temperature performance of the joint. Cracks are initiated from the MoNb solid solution, and then intergranular fracture propagates across the central diffusion layer. Reliable MHC/ GH4099 bonding joints are obtained with Nb-Ni interlayer at 1 150 ℃/130 MPa/180 min in HIP process. The joint tensile strength/shear strength with Nb+Ni interlayer reach 84 MPa/41 MPa, which is higher than that with Ni-CrSi-B, Ag-Cu-Ti or Ti-Cr-Ni interlayer.

Based on the test and analysis of static mechanical properties of TA15 titanium alloy samples formed by selective laser melting, the fatigue properties of TA15 titanium alloy samples formed by selective laser melting at room temperature were studied and analyzed. Tensile properties, impact properties and fatigue properties of TA15 titanium alloy samples at room temperature were tested by universal testing machine, impact testing machine and fatigue testing machine. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to analyze the microstructures of the cross-sectional and longitudinal sections, as well as the tensile and fatigue fractures of the samples. The research shows that the cross section presents a typical checkerboard lattice structure, and the longitudinal section distributes β columnar crystals penetrate through multiple deposition layers and grow epitaxially, and acicular martensite is staggered inside the columnar grains. The tensile strength of the transverse and longitudinal samples after annealing treatment, the strength and yield strength are lower than that of the as-deposited samples, and the elongation, shrinkage and impact strength are significantly improved, and they are all better than the TA15 bar index. The fatigue life data has a certain dispersion, which is the main reason for the fatigue dispersion. It is a selective laser melting and forming process. The metal powder is rapidly melted and cooled under the action of a high-energy laser, and defects such as poor overlap, pores, and unmelted powder appear randomly inside the part. The depositional cross section of TA15 titanium alloy formed by selective laser melting presents a typical checkerboard lattice structure. The longitudinal section is distributed with β columnar crystals growing epitaxial through several sedimentary layers. The columnar crystals are interleaved with acicular martensite. The ratio of length to width of primary and secondary α phases in annealed microstructure decreases continuously, and the spicules are coarsened continuously to form strip. After being held at 850 ℃ for 2 h, the tensile strength and yield strength of the transverse and longitudinal samples of TA15 titanium alloy decrease, while the elongation, shrinkage and impact strength of the samples are significantly increased, which are better than those of TA15 sheet. Fatigue life data of annealed TA15 titanium alloy in selective laser melting forming (stress ratio R=0.06, Kt=2.5) have a certain dispersion. The main reason for the fatigue dispersion is the rapid melting and cooling of metal powder under the action of high energy laser. Defects such as poor lap joint, air hole and unmelted powder appear randomly in the parts.

With the rapid development of aerospace and rail transit, single metal material is difficult to meet the requirements of light weight and high strength. Heterogeneous composite materials combined with two or more metal materials can obtain a good combination of strength and toughness. 7075 aluminum alloy has high strength and low density, and TC4 titanium alloy is the most widely used titanium alloy with both strength and toughness. Therefore, 7075 aluminum alloy and TC4 titanium alloy are combined to obtain bimetallic composites with excel‐ lent properties.In this paper, TC4 titanium alloy honeycomb topological structure preform was prepared by Selec‐ tive Laser Melting technology, and 7075 aluminum alloy melt was infiltrated at 700/750/800 °C by vacuum pres‐ sure infiltration to obtain 7075/TC4 composites. The area of 7075 aluminum alloy in 7075/TC4 composites is main‐ ly composed of fcc-Al, Al3Fe and MgZn2. The region of TC4 titanium alloy is mainly composed of lamellar α phase and β phase. The interface layer is mainly composed of Al3Ti, and its thickness increases from 6 μm at 700 °C to about 300 μm at 800 °C. When the infiltration temperature is 750 °C, the properties of the composites are the best, and the yield strength, compressive strength and fracture strain are (755±5) MPa, (1 136±12) MPa and 23%±1.5%, respectively. The fracture behavior of the composite material is as follows: the crack initiates at the grain boundary of the aluminum alloy region. With the increase of load, the cracks in the aluminum alloy area expand, and the cracks initiate at the defects of the interface and the titanium alloy area. With the further increase of the load, cracks in the aluminum alloy region expand to the interface, and connect with the cracks in the interface and the ti‐ tanium alloy structure region, resulting in material failure. At different infiltration temperatures, the phase composi‐ tion of the composite 7075 aluminum alloy region, TC4 titanium alloy region and interface region is similar. How‐ ever, the thickness of the interface layer increases with the increase of infiltration temperature. With the increase of infiltration temperature, the compressive strength and compressive plasticity of the composites first increase and then decrease, and reach the best at 750 °C. The grain boundary second phase, infiltration defects and SLM defects have adverse effects on the properties of the composites.the

3D printing is a new type of manufacturing technology, which is widely applied in the field of aero‐ space, medical treatment, automobile, ships.Titanium alloy is an important part of metal 3D printing system due to its excellent properties such as light weight, high specific strength, good corrosion resistance and excellent biocom‐ patibility. The performance requirements of titanium materials and main preparation methods of powder of 3D printing were briefly described. The characteristic of GA and PREP preparation technique were compared, and the reason for the difference of GA and PREP preparation technique were explained emphatically. At last, research directions and application prospects were expounded.

The friction pairs in wet clutches can cause drag torque and associated energy loss, when friction discs are not engaged, due to the viscous fluid nature of the lubricant subjected to relative motion between the friction pairs. This phenomenon is detrimental to the service life of wet clutches and causes concern of risk. In addressing this issue, based on the Navier-Stokes equation, a total of 12 groove designs with 24 configurations are designed and analyzed by means of finite element numerical simulation to explore the methods of reducing the drag torque and energy loss. The results show that the combination of spiral groove and radial non-slot design has good cooling effect and high dynamic friction coefficient. This paper provides an important reference for the design of friction pairs oil grooves, which is of great significance for guidance.

The technology of producing ultra-fine iron powder by hydrogen reduction is studied, using iron oxide red of pickling waste in steel works as raw material, the cost is less than one third of the cost of producing ultrafine iron powder by carbonyl method. The properties of the products are TFe≥98.5% , loose density is 0.80~1.20 g/cm3, free grain size D50≤16.5 μm, specific surface area is more than 2.10 m2/g. It is widely used in ultra-hard diamond tools, powder metallurgy injection molding materials, high-specification soft magnetic materials, adsorption materials, aerospace materials, food and other fields.

The development history of powder titanium alloy prepared by hot isostatic pressing technology for more than 60 years and the present situation of research and development in the world were reviewed. The problems encountered in the market development in the field of aerospace were analyzed， and the solutions were also put forward. At last the future trends of the technology were presented.

According to the principle of 3D printing, the 3D printing process of metallic materials can be divided into five categories: powder bed fusion, directed energy deposition, binder jetting, material jetting, and sheet lamination. The basic principles, advantages and disadvantages, application fields and progress of the main technologies under various processes are introduced. Finally, several mainstream 3D printing technologies are compared, and it is pointed out that SLM and EBM have become the mainstream of powder bed fusion process and are suitable for small and super-complex monolithic components; directed energy deposition technology uses laser, electron beam or arc as energy sources to melt and deposit materials synchronously, which has high processing efficiency and is suitable for large and high-performance integral components. The binder jetting has a potential application in the manufacturing industry which needs rapid casting manufacturing because of its low production cost and short cycle. The development trend of 3D printing of metal materials is prospected.

In this paper，the plasma nitriding process was carried out to treat the surface of H13 hot die steel. The experimental results show that the samples with the best property are achieved when the nitriding temperature is 500 ℃ and the holding time is 8 h，while the surface hardness is 1 250HV and nitriding layer thickness is 241 μm. The friction and wear test show that the wear loss quality of die steel samples with nitriding temperature of 500 ℃ and holding time of 8 h is 206 mg after 14 h of wearing test. The phase composition shows that the main compounds in nitriding layer are Fe₂N，Fe₄N and Fe₃O₄.The compound layer and nitriding layer with appropriate thickness have significant effect on the improvement of thermal properties of die steel.

The automotive industry is one of the most important markets and main applications of new technolo‐ gies for worldwide powder metallurgy industry. This article introduces the development situations of China′s pow‐ der metallurgy industry, and briefly introduces the developments of auto PM parts market and home appliance PM parts market in recent years which are the most important markets for powder metallurgy industry in China. It also briefly introduces the development trend of the global automobile industry responding climate changes, as well as the development of new energy vehicles in China. The concept of“powder metallurgy+”process is put forward based on the basic understanding of PM as a“green”technology in PM associations of Europe and Unit‐ ed States, and it is compared that of the raw materials utilization rate and energy consumption per weight finished products between“powder metallurgy+”and other metal processing processes on the basis of actual measure‐ ment in this article. The results indicate that the“powder metallurgy+”process is a more resource-saving“green manufacturing”technology. The opportunities and challenges are given for developing China′s powder metallur‐ gy parts industry under“carbon peaking and carbon neutrality”target.

In this paper, the basic principle of first principles in material calculation is briefly introduced, and its progress in the research of superconducting materials, especially in the field of superconductivity, is summarized, which provides theoretical support for the further development of new superconducting materials and their practi‐ cal application; The shortcomings and suggestions of first principles calculation in the field of superconducting materials are put forward, and its research prospect in the mechanism of superconducting principles is prospected.

The use of metal powder injection molding (MIM) technology to produce small metal parts with com‐ plex geometric shapes, especially for transmission parts with similar and repeated features, such as small module gears, had certain advantages. As for the selection of metal gear materials, stainless steel 17-4PH could be used in‐ stead of MIM technology. The mechanical properties and corrosion resistance of this material are superior to those of traditional machined gears. In this paper, according to the characteristics of stainless steel 17-4PH, gears were made by MIM process and heat treated under different conditions (after sintering, H900, H900+annealing). After quality testing, there is a slight change, which is similar to the results of traditional hot rolled plates. MIM process could make complex gears, maintain the excellent dimensional accuracy of stainless steel 17-4PH, and improve me‐ chanical properties.

In order to improve the surface hardness and wear resistance of 316 stainless steel for vehicle used, FeCrCoNi high entropy alloy coating were prepared on the surface of 316 stainless steel by laser cladding in situ synthesis. The phase composition, element distribution, microhardness and wear resistance of FeCrCoNi high entropy alloy coating were studied. The results show that the FeCrCoNi high entropy alloy coating prepared in situ has no cracks, pores and other defects, and has good metallurgical bonding with the substrate. FeCrCoNi high entropy alloy coating is composed of a single FCC phase with dendrite and interdendrite structures. All elements are evenly distributed without obvious segregation. The microhardness of FeCrCoNi high entropy alloy coating is 287.3 HV, which is about 50% higher than that of 316 stainless steel substrate. The average friction coefficients of FeCrCoNi high entropy alloy coating are 0.377 and 0.438, respectively, and the wear rate of FeCrCoNi high entropy alloy coating is 70% lower than the wear rate of 2.27×10-5 mm3/N·m and 6.17×10-5 mm3/N·m, respectively. The wear mechanism of FeCrCoNi high entropy alloy coating is abrasive wear.

Nickel-cobalt-manganese ternary materials have become the best choice of lithium cathode materials for 3C, power tool and selectric vehicles due to its high capacity and high density. In order to avoid side reaction between electrolyte and cathode materials and enhance the conductivity of cathode material, it is particularly impor‐ tant to modify the cathode material. In this paper, Al（2 SO4）3 and CoSO4 were used as coating raw materials. NaOH was used as precipitator. The surface of the precursor was coated with a layer of aluminum hydroxide and cobalt hydroxide by wet coating, and then oxidized to obtain AlOOH and CoOOH. The materials were characterized by LS-POP9, BET, TD, SEM, XRD and electrochemical test. The results show that the sintered cathode material has good capacity retention and cycle performance. In the test for 0.2C（3.0-4.3 V）, the specific capacity reaches 175 mAh/g, the initial charge-discharge efficiency, and it is excellent with 100% capacity retention rate after 50 cycles. It can be seen that the double-layer composite coating method provides a way to improve the performance of lithium anode materials.

The effects of gas, solid-liquid ratio, PH, batch separation time and nucleation time on the morphology of Ni 0.55Co0.50MN0.40(OH)2 were studied by co-precipitation experiment. The results show that when the PH value is 10.5~10.6, the ratio of solid to liquid is 8% , the batch separation time is 1 t≤m≤2 t, the separation reactor is not needed and the nucleation time is 1.5 h, Ni0.55Co0.50MN0.40(OH)2 with good morphology can be synthesized.

Sintered metal filter tube is the core element in the high-temperature gas filter, whose filtration perfor‐ mance is directly related to the downstream safety production. In this paper, through the analysis of the circulating pressure drop of the sintered metal filter tube, the dynamic pressure change inside the sintered metal filter tube dur‐ ing the pulse-back process, changes in the thickness of the dust cake, the shedding of the dust cake and the outlet concentration, it is found that the sintered metal filter tube has the better filtration performance, the concentration of particles is less than 10 mg/m3, the particle size distribution is basically below 1 μm, which meets the filtration requirements. The dynamic pressure change inside the filter tube is consistent with the trend of the thickness of the dust cake changing with time. When the dynamic pressure inside the filter tube reaches the maximum, the dust cake is also fluffy to the maximum. The cycle performance regeneration function of the sintered metal filter tube could be completed by using a low pulse-back pressure combined with the dynamic pressure change inside the fil‐ ter tube, thickness of the dust cake and the shedding of the external dust cake.

In this study, the surface modification treatment of FeSiCr alloy powder was carried out with zinc-man‐ ganese phosphating solution. Vibrating sample magnetometer, impedance analyzer and soft magnetic material AC test device were used to analyze effects of the content of zinc-manganese phosphating solution on saturation mag‐ netization of FeSiCr magnetic powder, effective permeability and power loss of FeSiCr magnetic powder cores. The results show that with the increase of the concentration of zinc-manganese phosphating solution, the saturation magnetization of the composite magnetic powder core gradually decreases, the power loss first decreases and then increases. When the concentration of zinc-manganese phosphating solution is 25%, the effective permeability is 39.5, and the power loss is only 103.6 W·kg-1 (100 kHz, 50 mT).

The research status of 3D printing technology in the aerospace field was summarized in this paper, the characteristics of geometric components with complex structures and topology optimization processed by 3D print‐ ing technology were introduced. The development of 3D printing preparation technology applied in the aerospace field at home and abroad was emphatically described, including metal based materials, directed energy deposition technology (DED), powder bed fusion molding (PBF) and post-processing technologies, as well as manufactured aerospace components. The advantages-disadvantages of 3D printing technology in the aerospace field were sum‐ marized, and technical improvement and research direction were prospected.