Molybdenum disulfide has been widely used in electronic devices, catalysts, and biomedical fields, due to the special layered structure and the unique properties. The lubrication performance, photoelectric performance, and catalytic degradation properties of molybdenum disulfide were briefly reviewed in this paper, the application and research status of molybdenum disulfide in lithium-ion batteries, supercapacitors, biomedicine, biosensors, and photocatalysis fields were introduced, and the future development trend of molybdenum disulfide is proposed based on the research background and development status.

The foamed metals have become the new structural functional materials with the excellent properties of heat, sound, light weight, and energy absorption. Known as the “metal star”, the porous aluminum foam is the most popular foam metals with the most potential application, showing the excellent performance as low density, high temperature resistance, good corrosion resistance, non-flammable, good weather resistance, low thermal conductivity, high electromagnetic shielding, high energy absorption, and good noise reduction, which is widely used in the automobile industry, the aeronautics and astronautics industry, and the construction industry. In this paper, the structural characteristics and physical properties of the aluminum foams are reviewed, and the preparation, process principle, and characteristics of the aluminum foams are summarized.

Development and preparation of heat conducted resin composites filled with hexagonal boron nitride (hBN) used in electrical and electronics field were studied. The mechanism and model of thermal conductivity were introduced. The effects of morphology, particle size, particle mixing, and surface modification of hBN filler on the resin composites were discussed. Finally, the prospect of the resin composites filled with hBN was proposed.

Thermal barrier coatings (TBCs) can effectively improve the operation temperature and service life of aero-engine hot end components. At present, yttria-stabilized zirconia (YSZ) is the most widely used thermal barrier coating materials. Phase transformation of YSZ occurs when the service temperature is higher than 1200℃, which seriously affects the service life and service safety of the aero-engines, and it is difficult to meet the service requirements of new generation of aero-engines. The investigation on the advanced thermal barrier coating materials (TBCs) was summarized in this paper. The research progress of several novel thermal barrier coating candidates were mainly reviewed, such as multiple oxide co-droped YSZ, A₂B₂O₇-type compounds, perovskites, magnetoplumbite compounds, and new bond coating materials. The preparation principles and advantage-disadvantage of thermal barrier coatings were discussed. At last, the development direction of thermal barrier coating materials and preparation technology were also proposed.

Additive manufacturing can produce the arbitrary complex shape parts, which has the advantages of fast, efficient, economical, fully intelligent, and fully flexible manufacturing. Based on the introduction of the typical metal additive manufacturing technology at home and abroad, the application of the metal additive manufacturing technology in the field of nuclear industry was overviewed in this paper, the performance of nuclear material products prepared by the additive manufacturing was summarized, and the advantages of the metal additive manufacturing in the field of nuclear industry were proved by the practical cases. At the same time, the development trend of the additive manufacturing technology in the field of nuclear materials was forecasted based on the application background of the innovative reactor technology for the nuclear materials.

Aluminum nitride has been widely applied for the high thermal conductivity and insulating properties. Nowadays, the global aluminum nitride application market is in the high growth stage as well as the demand for aluminum nitride is growing continuously. Aluminum nitride powders are the critical raw materials for the synthesis of aluminum nitride ceramics, and the properties of the aluminum nitride powders dominate the properties of the aluminum nitride ceramics. In the paper, the preparation methods of micrometer- and nanometer-sized aluminum nitride powders have been compared. Moreover, the future research directions and development trend of preparing aluminum nitride powders have been pointed out.

With the quantity production of the powder metallurgy parts with the excellent comprehensive performance and complex shape, the computer simulation technology is widely used in powder metallurgy process to reduce the product cost, improve product quality, and shorten the development cycle. Several simulation software (Abaqus, Deform, Ansys, Comsol, and MSC.Marc) were introduced in this paper, which are widely used in powder metallurgy field at present. The advantages and disadvantages of the simulation software were compared. The application and selection for the simulation software in the actual production practice were also discussed. The expectation and development of the computer simulation software in powder metallurgy field in the future were put forward.

The fabricating processes of the high-entropy alloys (HEAs) fabricated by the laser additive manufacturing were briefly introduced in this paper. The recent research progresses on the laser additive manufacturing of HEAs were reviewed, especially in terms of forming process, element content (molar fraction), heat treatment process, and enhanced phase. Laser melting deposition (LMD) and selective laser melting (SLM) processes were compared and analyzed, and the microstructure and mechanical properties of HEAs fabricated by LMD and SLM were investigated. Finally, the development trend and the major problems of HEAs prepared by the laser additive manufacturing were point out, and the improvement measures were proposed.

With an excellent combination property of low density, high specific strength, fantastic bio-compatibility, and good corrosion resistance, titanium and titanium alloys are becoming promising materials in the field of aerospace, bio-medical, chemical industry, automobile, etc. Metal injection molding (MIM) can realize small and medium-sized products of titanium and titanium alloys with complex shape by low cost and mass production, which makes the MIM technique have the great significance in promoting the development and application of titanium and titanium alloy products. In this paper, the main characteristics and advantages of titanium and titanium alloys fabricated by MIM were briefly introduced. The recent research progresses on MIM of titanium and titanium alloys were reviewed, especially in terms of feedstock powders, binder systems, injection molding, debinding, and sintering processes. Finally, in view of the existing problems, the further development and research direction on metal injection molding of titanium and titanium alloys were investigated.

Metal additive manufacturing technology is now developing in the direction of industrialization, and the titanium powders are one of the mainstream raw materials used for metal additive manufacturing. The smelting technology of titanium and its alloys was summarized in this paper, the induction smelting was emphasized, and the main technology of titanium powder preparation was analyzed and compared, including the basic principles, the characteristics, and the factors affecting the powder characteristics. In addition, the application of numerical simulation on the titanium powder preparation was also introduced, and the development of titanium powder preparation technology used in the field of metal additive manufacturing was prospected.

316L stainless steel powders used in 3D printing were prepared by a vacuum inert gas atomization (VIGA) system in this paper. The effects of atomization pressure on the chemical composition, particle size distribution, sphericility, surface morphology, flowability, and apparent density of 316L stainless steel powders were investigated. The results show that under the certain process parameters (melting at (1560 ±20)℃, holding for 20 min, tundish temperature at (1050 ±30)℃, and N₂ atomization at 3 MPa), the high quality 316L stainless steel powders can be obtained, which can be used for different 3D printing techniques. The characteristics of powders are summarized as the oxygen content of 0.08% by mass, the medium diameter (D₅₀) of 31.39 μm, the sphericility of 0.75, the fluidity of 21.56 g/(50 s), and the loose packed density of 3.88 g/cm³.

The preparation technologies of high density iron based powder metallurgy products used in NBTM were introduced in this paper, including warm compaction, warm die compaction, double-pressing and double-sintering, and the advantages and disadvantages of these technologies were discussed. Although the preparation technologies described in this paper can improve the density and strength of powder metallurgy parts to a high level, the precision and roughness of the parts cannot meet the requirements of high-level applications, and the further machining is still needed. For the iron-based powder metallurgy parts, the precision of powder metallurgy die manufacturing, the powder characteristics, and the process stability are still needed to improve in the future, and the new sintered iron based parts preparation technology with low-cost, high-precision, and high-strength should be developed.

Application of pure molybdenum is extremely limited due to the shortcomings of high ductile-brittle transition temperature, embrittlement after recrystallization, and deficient performance on high-temperature oxidation resistance. However, by adding a second phase (rare earth oxide (La₂O₃, Ce₂O₃, and Y₂O₃) and carbide (TiC, ZrC, and HfC)) to form molybdenum alloy, the properties of molybdenum get significantly improved, which arouses the wide attention domestically and abroad. The preparation technology of molybdenum alloy (solid-solid doping, solid-liquid doping, and liquid-liquid doping) was summarized and the development tendency was illustrated in this paper. The results show that the liquid-liquid doping process can significantly improve the homogeneity and mechanical properties of materials.

Metal powder injection molding (MIM) can be used to manufacture the high performance precision parts with the special shape in large quantities and low cost, which is regarded as one of the research hotspots in the field of the advanced manufacturing technology. The MIM technology was summarized in this paper, including the powder preparation, the binder selection, the mixing, the injection, and the subsequent debinding and sintering. The development, status, and new technology of MIM were introduced, the numerical simulation of MIM was deeply analyzed, and the development trend of MIM was prospected.

The research progress on the microwave sintering mechanism of metal powders was reviewed in this paper from the aspects of the electromagnetic effect on metal powders in microwave field and the sintering behavior of metal powders in microwave field. In the electromagnetic effect, the influences of thermal effect and non-thermal effect on sintering behavior were introduced, respectively. The thermal effects of sintering mainly included the electromagnetic power loss caused by microwave heating and the electromagnetic focusing phenomenon. The non-thermal effects mainly included the microwave discharge effect and the magnetic effect. In the sintering behavior, the material migration mode and the growth mechanism of sintering neck during the growing process were reviewed, the material migration mode was influenced by the material type and process parameter, and the growth of sintered neck was closely related to the temperature field and electromagnetic field. Based on the review of current research progress, the shortcomings and deficiencies were analyzed, and the future research direction of the microwave sintering mechanism was also proposed.

Nanodiamond has the dual characteristics of the diamond and the nano-materials. Due to the sp³/sp² hybrid structure of core and surface and the abundant surface dangling bonds and functional groups, the nanodiamond shows the broad application in the fields of lapping and polishing, antifriction and lubrication, composite material reinforcement, drug delivery, and fluorescence absorption. The nanodiamond particles agglomerate in hundreds of nanometers and need to be dispersed into the different liquid phase systems by various means. The research on the dispersion methods of the nanodiamond was summarized at home and abroad in this paper, and the principle and characteristics of the dispersion methods as the mechanical method, the inorganic chemical method, the high energy field treatment, and the surface organic chemical modification were analysed.

As one of the new technologies for the high-performance complex metal components, the additive manufacturing technology has been used in the aerospace, automotive industry, medical, and nuclear powder fields. The metal additive manufacturing processes involve the complex physical phenomena such as heat transfer, thermal, phase transition, and flow. Numerical simulation methods in the different scales and cross-scales combined with the experimental verification can realize the understanding, control, and optimization of the complex physical phenomena in the additive manufacturing process, which can provide the strong support for the forming of high-quality, high-precision, and high-performance metal components. The numerical simulation of metal additive manufacturing processes in the macro, mesoscopic, micro, and multi-scale was reviewed in this article. The numerical simulation methods of temperature field, thermal stress field, powder bed, molten pool flow, and solidification behavior process were described. Finally, the development trend of the numerical simulation methods for the additive manufacturing was prospected.

High-quality metallic powders are essential for the selective laser melting (SLM) technology. The powder characteristics are indispensible for the understanding of SLM technology. The influences of powder physical and chemical characteristics on SLM processing, component microstructure, and mechanical properties were reviewed in this work. For the physical properties, the powder morphology and powder size distribution could significantly influence the powder flowability and powder-bed packing density, which were vital for the subsequent laser melting. On the other hand, the chemical compositions, especially the contents of impurities, determined the phase constitutes and microstructures. Furthermore, the recent progress on the interaction between laser and powder and the corresponding metallurgical mechanism were also introduced.

B₄C is a critical industrial material, which is widely used in parts processing, aerospace, armor protection, and nuclear industry. Spark plasma sintering (SPS) technology can realize the rapid sintering of materials at low temperature through the multi field coupling. The research status of B₄C ceramics sintered by SPS in recent years was reviewed in this paper. The basic principle and characteristics of SPS were expounded. The effects of the raw powders and sintering parameters on the composition and properties of B₄C were emphatically analyzed. Finally, the development of B₄C ceramics sintered by SPS was prospected.

Titanium and titanium alloys have the low specific gravity, high specific strength, excellent biocompatibility, and good corrosion resistance, showing the great application potential in the aerospace, biomedicine, chemical engineering, shipbuilding, automobile, and other fields. The powder injection molding (PIM) technology used for titanium alloys increases the utilization rate of materials, realizes the large-scale and low-cost preparation of small and medium-sized titanium products with complex shape, and significantly promotes the development of titanium and its alloys. At present, there are few reports about the titanium alloy binder system for powder injection molding, and the development of new type titanium alloy binder system for powder injection molding is in a stagnating state. The research status of the different titanium alloy binder systems for powder injection molding was introduced in this paper, and some improvements for the existing problems were suggested as the reference for researchers.

Particle-reinforced titanium-based composites are widely used in aerospace, automotive, and medical engineering due to their high strength, light weight, corrosion resistance, and excellent high temperature mechanical properties. The development overview and research results of titanium-based composites in domestic and international were introduced in this paper. The matrix composition of titanium-based composites, the morphology and physical properties of particle reinforcement materials, the introduction method of reinforcement, the preparation process, and the mechanical properties of the composites were described. Especially, the process characteristics and material properties of the particle-reinforced titanium-based composites prepared by the different powder metallurgy methods were discussed, and the propose prospects for the further research on titanium-based composites were expected.

Numerical simulation can provide the theoretical guides and technical supports for the design and optimization of process, the prediction and prevention of manufacturing defects, and the performance promotion of parts in powder metallurgy. Mathematical models for precisely describing powder compaction and sintering process are the foundation of successful numerical simulation. In this paper, the mathematical modeling methods for powder compaction, including sintered powder plastic mechanics, generalized plastic mechanics, and micro-mechanics, as well as the micro-structure simulation methods in powder sintering process, including molecular dynamic method, phase field method, Monte-Carlo method, and cellular automatic method, were briefly introduced; also the calculation principle, application scope, and recent research development were analyzed; at last, the future advancements of numerical simulation in powder metallurgy were discussed.

The research and development of particle-reinforced magnesium matrix composites prepared by powder metallurgy were summarized in this paper, the substrate and the micron-scale/nanoscale reinforcements commonly used for the particle-reinforced magnesium matrix composites were introduced. The powder metallurgy process was systematically described, including the pretreatment process of reinforcements, the molding process of mixed powders, and sintering process. The influence of powder metallurgy technology on the microstructure and mechanical properties of the composite was investigated, including the interface bonding between reinforcement and matrix and the particle reinforcement strengthening mechanism. Finally, the development prospect for the preparation of the particle-reinforced magnesium matrix composites by powder metallurgy was expected, and the improvement measures were proposed.

Additive manufacturing technology breaks through the limitations of traditional mold processing technology, and it is an important method for the efficiently customizing biomedical materials. Recently, the personalization needs of medical bone repair and transplantation have increased significantly. The customized and individualized advantages gradually promote the additive manufacturing technology to play an important role in the field of biomedical materials. With the development of materials science and computer aided technology (CAD/CAM), the biological implant materials used for additive manufacturing are no longer limited to the alloys such as titanium alloys, tantalum alloys, and vitallium. Because of good biocompatibility, the non-metal materials such as polyetheretherketone (PEEK) and calcium phosphate are widely used in biomaterials. The preparation of artificial bone implants by additive manufacturing technology has become a new research hotspot. The principle of additive manufacturing technology was reviewed, and the manufacturing techniques by laser, electron beam, and photocuring were compared in this paper. The application status of additive manufacturing in biological implants and medical devices was introduced, and the development prospects of additive manufacturing technology in medical field were prospected.

To improve the catalytic efficiency of zinc ferrite, the specific surface area is increased, and the surface morphology of zinc ferrite is optimized. Besides, the zinc ferrite is combined with other materials to obtain more efficient and practical photocatalyst. The modification methods of zinc ferrite and the preparation methods of zinc ferrite with different morphologies were analyzed and summarized in this paper, and the particle size unevenness after the modification and the research direction were briefly discussed and prospected. The zinc ferrite combined with other materials can prepare the composite photocatalyst with high activity and stable performance, which can improve the catalytic ability of the composites and alleviate the problem of low catalytic activity of zinc ferrite. The preparation of zinc ferrite with different morphologies can increase the specific surface area of zinc ferrite, improving the catalytic efficiency of zinc ferrite.

Molybdenum and molybdenum alloy sputtering target materials have been widely used in the fields of electronic industry, solar cell, and glass coating because of their high melting point, good thermal and electric conductivity, low thermal expansion coefficient, good corrosion resistance, and environmentally friendly performance. The basic requirements and preparing methods were introduced in this paper firstly. The main research status of Mo, Mo-Ti, Mo-Na, and Mo-Nb at home and abroad was systematically reviewed, and the development trend of molybdenum and molybdenum alloy sputtering target materials was presented.

The research progress of the molybdenum-based composites prepared by powder metallurgy (PM) technology was summarized in this paper, the common reinforcements of the molybdenum-based composites and the effects of the reinforcements on the properties of the molybdenum-based composites were introduced. The preparation technology of the molybdenum-based composites were emphatically described, including the technology of preparing molybdenum powders, the method of preparing composite powders, and the technology of powder forming and densification. The advantages-disadvantages and effects of the preparation technology on the molybdenum-based composites were studied. The problems existing in preparing the molybdenum-based composites by PM were summarized, and the development directions of the molybdenum-based composites by PM were prospected.

Graphene is used as an ideal reinforcement in composites, due to its characteristic structure and superior physicalchemical properties. The preparative technique of aluminum matrix composites reinforced by graphene, especially the dispersion of graphene and the forming of composites, were overviewed in this paper. Effect of preparation method on aluminum matrix composites reinforced by graphene was also discussed. New powder blending and sintering method for the preparation of graphene/aluminum matrix composites was proposed.

Foam metal is a new type of structural functional material, which is composed of metal matrix and pores. Compared with the solid metal materials, foam metal materials obtain some advantages such as heat, sound, energy absorption, and light weight at the expense of mechanical properties such as strength. Aluminum foam is a lightweight porous metal material which contains many pores in the aluminum matrix and combines metal and bubble characteristics. Aluminum foam shows low density, high absorption and shock resistance, high temperature resistance, strong fire resistance, corrosion resistance, noise reduction, low thermal conductivity, high electromagnetic shielding, strong weather resistance, filtration capacity, excellent penetration, damping, and electromagnetic shielding, which is widely used in metallurgy, chemical, aerospace, marine, electronics, automotive manufacturing, and construction industries. The researches on preparation method and physical properties of aluminum foam are important to improve the performances and expand the application fields of aluminum foam. The research progress on preparation and physical properties of foam aluminum and reinforced aluminum foam composites was summarized in this paper.

3D printing, also known as additive manufacturing (AM), is a technology that uses 3D design data to build physical parts by adding materials layer by layer. With the application of information technology and intelligent control to 3D printing technology, the 3D printing technology is becoming more and more mature and commercialized gradually. The rapid development of manufacturing technology often requires the rapid follow-up of design technology. Topology optimization method has become an important tool for the structural innovative design because it is independent of the initial configuration and the engineer experience and can obtain completely unexpected innovative configurations. Embedded technology is a device or system that is controlled by an internal computer and performs a special function. Compared with the general purpose computer systems, the embedded systems have the advantages in 3D printing, such as low power consumption, powerful functions, strong real-time performance, multi-task support, small space occupation, and high efficiency, and the specific applications can be customized according to the needs of flexible. The application of topology optimization design and embedded digital technology in 3D printing was summarized in this paper, the application cases of topology optimization and the mainstream software of topology optimization were introduced, the application advantages and cases of the embedded technology in 3D printing were analyzed, and the future topology optimization design and the application of embedded digital technology in 3D printing were prospected.

Positive temperature coefficient (PTC) thermal ceramics are a kind of key electronic functional ceramics, which are widely used in heating elements, sensors, circuit protectors, temperature controllers, and electrical demagnetization, because of the excellent characteristics. The positive temperature coefficient thermistor (PTCR) prepared by using BaTiO₃ as the host materials is a type of PTC elements with a large amount at present, showing the important research significance. The classification and advantages-disadvantages of the PTC heat-sensitive materials were elaborated in the article, the PTC effect, heat-sensitive mechanism, and semiconductivity principle of the BaTiO₃-based PTC materials were introduced, and the research status of the BaTiO₃-based PTC heat-sensitive ceramics was summarized at home and abroad. The effects of peak shifting agent, donor doping, acceptor doping, and sintering process on the BaTiO₃-based PTC thermal ceramics were analyzed. The application principle and application of the PTC thermal components were summarized in the related fields, and the lead-free PTC thermal ceramics were looked forward.

Copper-based powder metallurgy friction materials have been widely used in braking because of the superior performance. The utilization requirement of the copper-based powder metallurgy materials were described in this paper, and the application of the copper-based powder metallurgy friction materials on airplane, high-speed train, wind power turbine, and automobile were also systematically introduced. Furthermore, the development of the copper-based powder metallurgy friction materials was prospected, providing the reference for the further development of the copper-based powder metallurgy friction materials.

Based on the parameters of minimum ignition energy (MIE), minimum ignition temperature of dust cloud (MIT_C), and minimum ignition temperature of dust layer (MIT_L), the explosion sensitivity and influence factors of the typical metal powders used in additive manufacturing were investigated. The experimental results show that, the explosive sensitivity of nickel alloy powders and stainless steel powders is lower, while the explosive sensitivity of the titanium alloy powders is slightly higher than that of the aluminum alloy powders. The order of powder explosive sensitivity is as TA15>TC4>AlSi10Mg>316L>GH4169>GH3536>GH3625/304L. The results also show that, both nickel alloy powders and stainless steel powders could not be ignited. The MIE and MIT_C of titanium alloy powders and aluminum alloy powders decrease first and then increase with the increase of dust concentration, while decrease first and then increase with the increase of dust spraying pressure.

The effects of zinc stearate, ethylene bis stearamide (EBS), composite lubricant, and compaction temperature on the warm compaction process of Fe-based powder metallurgy (PM) materials were investigated by scanning electron microscopy (SEM) and properties tests. The results show that the apparent density and flow rate of Fe-based powders decrease with increasing lubricant content when the lubricant content is higher than 0.4%, and the effect of EBS is the greatest. The density of Fe-based PM green compacts increases by use of lubricants, and the particles combine more closely when zinc stearate and composite lubricant are used. The effect of lubricants on the green density, sintered density, and bending strength of Fe-based PM samples is composite lubricant > zinc stearate > EBS in order, and the density and mechanical properties of Fe-based PM materials increase with increasing compaction temperature. When the lubricant content is 0.4%, the density of Fe-based PM samples by warm compaction at 120℃ are improved by 0.14~0.21 g/cm³ compared to that of the conventional compaction samples, and the hardness and bending strength are increased by 40%~65%.

Effect of the heat treatment on the microstructure evolution and mechanical properties of the a P/M Ni-based superalloy in the diffusion bonding interface was studied by the optical microscope (OM), scanning electron microscope (SEM), electron probe microanalysis (EPMA), and elevated temperature tensile test. The results show that Cr, Mo, Co, W, Al, and Ti elements diffuse from the alloy matrix to the interface, which leads to the appearance of the obvious bond-affected zone. Ni element diffuses from the electrodeposited coating to the matrix, and reacts with Al and Ti to form the coarse γ' phases. The coarse γ' phases are distributed as a cluster band in the interface. The width of the bond-affected zone and the cluster band are changed by the further diffusion of Cr, Mo, Co, W, Al, and Ti elements after the sub solution treatment and super solution treatment. The tensile test at 650 ℃ shows that the fracture location of diffusion bonding interface includes both the interface and the matrix. A large number of dimples and a small amount of dissociation surface in the fracture surface are found, showing a ductile-cleavage mixed fracture mode. The interfacial strength increases significantly, but the interfacial plasticity decreases after the sub solid solution and aging treatment. The interfacial strength decreases and the interfacial plasticity further decreases after the super solid solution and aging treatment.

Spherical powders are the important raw materials used for the preparation technology as the additive manufacturing, powder metallurgy, and injection molding. The composition, particle size, sphericility, and hollow powder rate of the spherical powders are the key factors for the final component performance. Three kinds of manufacture techniques for the engineering superalloy spherical powders as the vacuum induction melting gas atomization (VIGA), electrode induction melting gas atomization (EIGA), and plasma rotating electrode atomization (PREP) used for the additive manufacturing were described in this paper, the characteristics and research progress of these three kinds of manufacture techniques were analyzed, the defect formation reason and control method of the powders prepared by these three kinds of manufacture techniques were discussed, and the development trend of the superalloy powder preparation technologies used for the additive manufacturing was proposed.

The progress and prospect on the sintering techniques of molybdenum and molybdenum alloys were summarized in this paper, including sintering theory, sintering equipment, and sintering processing parameters, and new sintering techniques. In the results, the sintering theory of molybdenum and molybdenum alloys still focuses on the traditional theory of powder metallurgy. The development of sintering technology is to obtain the fully densified, fine crystal, and homogenized sintered billets. The tendency of sintering technology is the closely combination of sintering equipment and tooling with new powder metallurgy technology, resulting in more cross-research. Fully densification, microstructure homogenization, fine crystallization, and precise shapes controlling of sintered complex shapes molybdenum products during the sintering processing of large molybdenum and molybdenum alloys billets will be the hot and difficult points on the studies of molybdenum and molybdenum alloys sintering techniques.

The discrete element model of the compression molding process was established by the EDEM discrete element software to optimize the process of NdFeB powders compression molding. The effects of the different molding conditions (pressing speed and friction coefficient) on the mechanical characteristics of the green pressing (compression force and pressing internal stress) were analyzed to provide the reference for the optimizing of the molding parameters. The results show that, the position of NdFeB powders is the same as that at the time of powder distraction during the molding process, but the powders near the die-stamping area displace greatly. The stress relaxation phenomenon occurs at the molding of green pressing. It is worthy noticing that the pressing speed has the different effects on the peak force of compression, but eventually it will converge to a similar stable value. The addition of lubricant can improve the internal stress state of the green pressing, reduce the compression force, and decrease the relative density of the green pressing. For the large-scale green pressing, the two-directional pressing should be adopted.

As the key part of turbine drive in the electronic parking brake system, the powder metallurgy helical gear was difficult to form because of the non-circular spline structure of inner hole. The structure, performance, material selection, and production process of powder metallurgy helical gear were introduced in this paper. In the results, the well-fluidity powder should be used to fill the helical region of female die. To avoid the fracture of core rod, the pressing machine with non-rotation lower punch is selected. According to the product requirements, the production process is as follows:compacting → sintering hardening → tempering → postprocessing; the compacting and sintering hardening are the key steps. By applying the applicable technology, the high-accuracy, high-strength, and complex-shaped helical gear can be produced, meeting the demand of working condition. The helical gear has been quantity production in stable quality, getting good economic benefits.

The tantalum and rhenium doped tungsten-based alloys were prepared by laser sintering, and the microstructure and mechanical properties of the tungsten-based alloy samples were investigated by scanning electron microscope (SEM), optical microscope (OM), X-ray diffraction (XRD), and micro-hardness tester. The results show that, the laser power and laser scanning speed are the important factors affecting the relative density of tungsten alloy blocks, the compact tungsten alloy block materials are obtained by optimizing the parameters. The powder oxidation is avoided by the desorption and deoxygenation pretreatment and the inert gas protection. The microstructures show that, the static recrystallization occurs in the laser sintering process. The equiaxial grains with the significantly larger size than the powder grains are formed at the core of the tungsten-based alloy sample, and the equiaxial grains with the size slightly larger than the powder grains size are formed at the edge of the tungsten-based alloy sample. The XRD results show that, the doped tantalum element exists as the solid dissolved atoms in tungsten matrix. The performance testing results show that, the density decreases with the increase of tantalum, but the microhardness increases.