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Effect of layer thickness ratio on microstructure and mechanical propertiees of TiC-WC/TiC-TiN laminated ceramics
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Abstract(11) PDF(142)
Abstract:
The TW/TT layered ceramics with five different layer thickness ratios(2:1、1:1、1:2、1:3 and 1:4, respectively) were prepared by dry pressing and vacuum hot pressing sintering technology with TiC as the matrix phase of each layer, WC and TiN as the additive phases of TiC-WC (TW) layer and TiC-TiN(TT)layer, respectively. The effects of layer thickness ratio on the residual stress, microstructure and mechanical properties were investigated. The results showed that there were residual compressive stresses in the TW layer, and the residual compressive stresses gradually increased with the increase of layer thickness ratio, and conversely, the tensile stresses presented in the TT layer gradually decreased. With the increase of the layer thickness ratio, the hardness and fracture toughness of the TW layer as well as the relative density and flexural strength of the material were first increased and then decreased, whereas the fracture toughness and hardness of the TT layer showed an decreasing trend. When the layer thickness ratio was 1:3, the fracture profile had higher density and fewer defects, and the best mechanical properties were obtained, its flexural strength was (946.01±19.1) MPa; Its hardness and fracture toughness in TW were (16.68±0.17) GPa and (10.19±0.22) MPa?m1/2, respectively; Those in TT were (15.73±0.15) GPa and (7.78±0.26) MPa?m1/2, respectively. It was also observed that the average grain size of the TT layer was significantly smaller than that of the TW layer. Crack deflection and crack bridging occured when the crack crossed the layer junction, and the fracture mode was dominated by transgranular fracture and intergranular fracture.
Research progress of K438 by electron beam additive manufacturing
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Abstract(15) PDF(2)
Abstract:
K438, Nickel-based superalloy, has excellent heat-corrosion resistance and high-temperature oxidation resistance, and is widely used in hot components of aero-engines such as turbine blades under working conditions of 900 ℃. Different from traditional preparation process, Additive Manufacturing (AM) technology has become an ideal process for "non-weldable" K438 superalloy due to its advantages of short production process, homogeneous microstructure and good high-temperature mechanical properties of components. Laser Source Additive Manufacturing (LSAM) in AM technology is prone to thermal stress accumulation and thus has a high susceptibility to cracking. Selective Electron Beam Melting (SEBM) technology is based on vacuum environmental conditions and powder bed preheating procedures, which can precisely control temperature changes and significantly reduce the residual thermal stress inside the workpiece, thereby reducing the number of cracks. In this paper, the current research status of K438 superalloy prepared by SEBM is reviewed, including the influence of working environment, process parameters and post-treatment technology on the quality of K438 superalloy, and the microstructure evolution trend of K438 superalloy under different process conditions, as well as the evolution of the phase organization of K438 superalloy under different process conditions.
Effect of Oxygen Content on Bending Strength and Thermal Conductivity of Aluminum Nitride Ceramics
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Abstract(8) PDF(3)
Abstract:
Aluminum nitride (AlN) ceramics exhibit high thermal conductivity, low thermal expansion coefficient, high strength, and resistance to chemical corrosion. Therefore, they are ideal materials for heat dissipation and packaging in large-scale integrated circuits, with significant applications in semiconductor technology, high-power electronics, and LED lighting and other fields. In this study, AlN ceramic samples were prepared using self-made AlN powders with varying oxygen content. The bending strength and thermal conductivity of the ceramics in the temperature range of 77 to 350 K were measured using the three-point bending method and the 3ω method. The influence of powder oxygen content on the bending strength and thermal conductivity of AlN ceramics was investigated, and the mechanical and thermal properties of Al2O3 ceramics, Si3N4 ceramics, and AlN ceramics at different temperatures were compared. The results indicate that AlN ceramics with low oxygen content exhibit high thermal conductivity and bending strength at room temperature and deep cryogenic temperatures. This study demonstrates the synergistic control of mechanical properties and thermal conductivity in AlN ceramics, highlighting their broad prospects for various applications.
Research status and prospect of ultra-high speed laser cladding
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Abstract(19) PDF(4)
Abstract:
Ultrahigh-speed laser cladding (UHLC) technology is a surface modification technology developed in recent years, which is favored by scholars at home and abroad because of its low dilution rate, small heat-affected zone and high efficiency. The article firstly introduces various surface modification techniques and compares them; secondly, it analyzes the materials used in UHLC, numerical simulation and experimental research of UHLC; thirdly, it elaborates the differences in microstructure and properties of coatings prepared by traditional and UHLC, and the practical application of UHLC; finally, it reviews the current problems of UHLC, and gives an overview of its application. Finally, the current problems of UHLC are summarized, and the development trend of UHLC is expected to provide reference for the subsequent experimental research.
Prediction of thermal conductivity of 93WNiFe alloys in sintering process via finite element analysis
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Abstract(51) PDF(4)
Abstract:
Tungsten heavy alloys are widely used in aerospace and microelectronics due to their excellent properties such as high melting point, high strength at high temperature and low coefficient of thermal expansion. Large refractory metal parts, especially large-size parts, have complex sintering processes, uneven sintering processes, and high production trial and error costs. Numerical simulation applied to the sintering process can play a good role in reducing consumption and increasing efficiency. Thermal conductivity (also known as thermal conductivity) as an important material thermophysical parameter required for numerical simulation of the constitutive equations, but the existing thermal conductivity measurement equipment and methods can not achieve the measurement of refractory metals at high sintering temperatures section. This paper is based on the use of finite element method to predict the thermal conductivity of 93W-Ni-Fe high specific gravity alloy refractory metal billet formed by cold isostatic pressing at different temperatures in the sintering process, and the prediction results are in good agreement with the experimental results, which indicates that the finite element method can achieve the ability to accurately predict the thermal conductivity of tungsten heavy alloys.
The influence of ingredient and preparation process on the microstructure of TZC molybdenum alloy
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Abstract(38) PDF(5)
Abstract:
Different sintering and hot-pressing processes are employed to prepare the TZC alloy with two doping methods of TiH2/ZrH2 and TiC/ZrC addition, respectively. The evolution of the microstructure and composition distribution of the alloy under different processing conditions was studied through optical metallographic observation, scanning electron microscopy analysis and phase analysis. The results show that the phase constituents of the two doping methods are basically the same, but in comparison with that for the alloy with TiH2/ZrH2 addition, the density for the alloy with TiC/ZrC addition after sintering increases from 9.21 g·cm-3 to 9.68 g·cm-3, and the hardness increases from 210 HV to 245HV, respectively. Hot pressing after sintering significantly increases the density and hardness of the alloy, and the grain distribution changes from a bimodal distribution in the sintered state to a unimodal distribution. It is found that the phase structures of the two kinds of additives undergo transformation during high-temperature sintering, of which determines the reaction diffusion process, thereby affects the changes in density and hardness. The alloy with TiH2/ZrH2 addition forms different characteristic regions in the microstructure after hot pressing. Fine-grained, dense, and high-hardness TZC alloy can be directly obtained by hot-pressing the alloy with TiC/ZrC addition.
Tribological behaviour of Cu-Zn based self-lubricating components reinforced with rare earth oxide Y2O3
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Abstract(31) PDF(14)
Abstract:
Cu-Zn-based self-lubricating composites containing rare-earth oxide Y2O3 and lubricating phase graphite were prepared by discharge plasma flash burning method, and the effects of the addition of rare-earth oxide Y2O3 and graphite on the mechanical properties and friction and wear properties of Cu-based self-lubricating composites were investigated. The results show that the friction coefficient of Cu-Zn alloy with 3 wt% graphite added is 63.6% lower than that of ordinary Cu-Zn alloy; the comprehensive performance of the composite with the addition of 1 wt% of rare-earth oxide Y2O3 in mass fraction shows a peak effect, with the hardness increased by 41.5% and the coefficient of friction reduced by 25%. Rare earth oxide Y2O3 in the matrix to produce diffuse strengthening effect, refine the grain and matrix pores, improve the density of composite materials, the formation of a continuous lubrication film with excellent tribological properties.
Effect of hot press sintering parameters on the microstructure and mechanical properties of Ti35421
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Abstract(58) PDF(9)
Abstract:
Ti-3Al-5Mo-4Cr-2Zr-1Fe (Ti-35421) was prepared using hot press sintering. In order to enhance the quality of titanium alloys prepared through this method, orthogonal experiments were conducted to investigate the effects of sintering temperature, sintering pressure, and holding time on the microstructure and mechanical properties of hot-pressed sintered Ti35421. The study aimed to determine the optimal sintering parameters. The results revealed that temperature and pressure play crucial roles in influencing the microstructure and mechanical properties of the sintered alloy. Increasing the temperature promotes alloy densification, resulting in higher density and hardness. However, elevated temperatures can also lead to grain growth, which reduces the compressive properties of the alloy. By using an appropriate temperature and higher pressure, the overall mechanical properties of Ti35421 can be significantly improved. The alloy exhibited the best compressive properties when sintered at a temperature of 900 °C, a pressure of 45 MPa, and a duration of 2 hours. Under these conditions, the alloy demonstrated a yield strength of 1248 MPa and a fracture strain of 23.03%.
Preparation of WC-xVC composite powder and the effect of high content VC on microstructure and mechanical properties of WC-Co based cemented carbide
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Abstract(20) PDF(3)
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In this work, WC-xVC composite powders were synthesized by a two-step carbothermal reduction process, and then WC-Co-VC cemented carbides with different Co contents (6 wt.% and 10 wt.%) were prepared by using WC-xVC composite powder as raw material. The effect of sintering temperature (1420 ℃, 1440 ℃ and 1460 ℃) on the densification of samples was studied. Meanwhile, the influences of Co and VC contents on the grain size of WC as well as hardness and fracture toughness were investigated. The experimental results indicated that as the sintering temperature increased, the relative density increased, and when the temperature was 1460 ℃, the relative densities were all higher than 98.5%. With the increase of VC addition amount, the average grain size decreased, leading to an improvement in hardness, while a decrease in fracture toughness. When the VC addition amount was 6 wt.%, the hardness reached the highest values of 1941 HV30 and 1838 HV30, for the alloys with the Co content of 6 wt.% and 10 wt.%, respectively. In addition, when the sintering temperature and VC content were constant, the increase of Co content would increase the fracture toughness and reduce the hardness.
Research progress on the effects of binder and powder properties on feeding properties of MIM
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Abstract(47) PDF(18)
Abstract:
In Metal Injection Molding, Injection, degreasing and sintering are carried out after the metal powder and binder are fully mixed to obtain the feed. The binder in the feed which has always been one of the research hotspots used is the core of the MIM. The rheological properties of the feed and the powder load are important factors for affecting the injection, degreasing and sintering processes. In this paper, the effects of binder components, additives, powder shape and particle size on the rheological properties and powder load of the feeders have been discussed. The additives to improve the feeding performance include compatibilizers, stabilizers, surfactants, etc. After adding the additives and optimizing the particle size distribution and shape, the rheological properties such as the viscosity and rheological parameter of the feed and the critical loading capacity of the powder are significantly improved.
Investigation of Microstructure and Performance at Weld Joints of Laser-Welded Diamond Saw Blades with Different Transition Layer Formulations.
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Abstract(54) PDF(13)
Abstract:
Laser welding of diamond saw blades is a critical tool in modern cutting industries, and its safety is directly influenced by the choice of transition layer materials. This study aims to investigate the influence of different transition layers on the performance and structure of laser-welded diamond saw blades. Through experiments, three different transition layer formulations were used to prepare sintered substrates and their diamond saw blades, followed by performance testing and structural analysis. The results show that the selection of different metal-based transition layer materials plays a crucial role in the quality and performance of the welding joints. Fe-based sintered substrates exhibit a moderate pore density and mixed fracture characteristics. Co-based sintered substrates have higher hardness and flexural strength but contain a greater number of evenly distributed pores. Cu-based sintered substrates exhibit higher density, uniform microstructures, and fewer, denser pores, displaying typical ductile fracture characteristics. Among the transition layer options, Fe-based saw blades exhibit the best tooth strength and weld joint quality, followed by Co-based blades, while Cu-based transition layers offer a cost-effective advantage. This study provides essential insights for diamond saw blade manufacturing, with the potential to improve their performance, enhance industrial cutting efficiency, and reduce costs. Further research can explore additional transition layer formulations and optimization paths to meet the requirements of various application fields.
Effect of oxides on the properties of Molybdenum-Rhenium plates
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Abstract(37) PDF(4)
Abstract:
The dispersed distribution of oxides can refine grain size and improve the mechanical properties of molybdenum matrix. There have been many studies on doping La2O3 and ZrO2 in molybdenum. Adding 14% mass fraction of rhenium to molybdenum can significantly enhance the strength and plasticity of the material, and improve processing performance at room temperature. This article investigates the effects of oxide doping on powder properties, sintering density, and room temperature mechanical properties by adding La2O3 and ZrO2 to molybdenum rhenium alloys, and compares the different effects of the two oxides. Research has found that doping with oxides can significantly reduce powder particle size and refine grain size, while doping with ZrO2 results in the smallest grain size but lower density; Rolling deformation can improve hardness and strength, doping La2O3 can obtain higher strength but unchanged elongation, and doping ZrO2 can improve strength while reducing plasticity; The effect of doping ZrO2 on strength enhancement is greater than that of doping La2O3, while the effect on elongation is opposite.
Research status on thermal load damage behavior of the tungsten-based plasma facing materials applications
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Abstract(27) PDF(5)
Abstract:
During the operation of nuclear fusion reactors, plasma facing tungsten-based materials need to withstand a certain number of times of steady-state and transient heat load without cracking, melting and other damage. This paper mainly summarizes the effects of alloying, dispersion strengthening and other modification methods on the thermal load damage behavior of tungsten-based materials. The heat load damage behavior of plasma facing tungsten-based materials was summarized and prospected.
Preparation of Al2O3/Cu porous composites by the combination of solution combustion synthesis and powder metallurgy method
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Abstract(50) PDF(13)
Abstract:
Al2O3/Cu composite powder was prepared by solution combustion synthesis and hydrogen reduction method using copper nitrate, aluminum nitrate, glucose and urea as raw materials. The Al2O3/Cu composite powder was uniformly mixed with the pore-forming agent sodium chloride, and then the mixed powder was cold-pressed. Finally, the Al2O3/Cu porous composite material (A-C-M) was prepared by sintering-dissolution process. The microstructure of powder raw materials and A-C-M were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The compression performance of A-C-M was tested by universal testing machine. The effect of glucose addition on the combustion product powder was studied. The effect of Al2O3 content on the compression performance of A-C-M was discussed. The results show that when the molar ratio of glucose to Cu(NO3)2 is 1, the specific surface area of the combustion product reaches a maximum of 12.5 m2·g-1. After the combustion product is calcined to remove carbon, the pores of the powder particles increase, but the specific surface area is reduced to 10.2 m2·g-1 due to the sintering effect of high temperature calcination. After the calcination product was reduced by hydrogen, the powder particles were broken into floccules. However, due to the sintering effect of high reduction temperature, the specific surface area of the obtained Al2O3/Cu composite powder was further reduced to 7.5 m2·g-1. With the increase of Al2O3 content, the porosity of A-C-M increases gradually, and its compressive strength decreases gradually.
Preparation of fully ceramic microencapsulated pellets of UO2/SiC and research of its high temperature thermal conductivity
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Abstract(49) PDF(8)
Abstract:
A series of UO2/SiC composite fully ceramic microencapsulated (FCM) pellets were prepared by self-grinding spheroidization coating and spark plasma sintering. The parameters such as heating rate, sintering temperature, sintering pressure, and SiC addition amount were regulated. The phase composition and structural characteristics of the pellets were observed by metallographic microscopy and scanning electron microscopy. The thermal conductivity (TC) of the pellets from room temperature to 1200 °C was obtained by a laser thermal conductivity meter. The effects of different process parameters on the microstructure and TC of the pellets were discussed. The results indicate that, the UO2@SiC composite particles are nearly spherical and well coated. The SiC matrix in UO2/SiC composite pellets exhibits a three-dimensional interconnected network structure. The sintering pressure has a significant influence on the structural integrity of UO2 particles in the pellets. The sintering temperature has a significant influence on the morphology and density of the SiC matrix. When the density is lower than 95 %, the sintering temperature has a greater effect on the TC of the fuel pellet, and when the density is higher than 95 %, the proportion of SiC added has a greater impact on the TC. The TC of the FCM pellets prepared in this study is increased by up to 256.6 % compared with pure UO2.
Research Progress on the Powders Preparation, Densification sintering, Microstructure and Properties of Tungsten Diboride (WB2)
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Abstract(52) PDF(9)
Abstract:
Tungsten diboride (WB2) has attracted great attention of researchers around the world due to its excellent mechanical properties, electrical conductivity, wear resistance, and neutron absorption ability. Therefore, it has been considered to have a wide application prospect as machining tools and wear-resistant materials. However, similar to other transition metal borides, the full consolidation of WB2 is difficult to achieve, and the reported experimental hardness values of WB2 are much lower than the theoretical hardness values, which severely limits its broad industrial applications. In the present work, the progress on synthesis methods of WB2 powders, sintering methods of WB2 bulk samples, and the effect of sintering aids on the microstructure and mechanical properties of WB2 ceramics were reviewed and summarized.
Preparation of boron carbide stainless steel composites by spark plasma sintering
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Abstract(51) PDF(139)
Abstract:
B4C microspheres and 304 stainless steel powder were used as raw materials, and the spark plasma sintering (SPS) method was used to produce B4C-stainless steel composites with a B4C content of 4%. The density of the composites was tested by the drainage method, the microstructures of B4C and stainless steel were analyzed by scanning electron microscope (SEM), which investigated the effects of sintering temperature and pressure on the density and microstructure of the composites. The results show that the thickness of the interfacial reaction layer increases with the increase of sintering temperature. Meanwhile, increasing the sintering pressure can significantly reduce the sintering temperature, which inhibits the growth of the interfacial reaction layer between B4C and stainless steel. When the pressure reaches 150 MPa, the density of the composites can reach 99.5% after sintering at 950 ℃ for 6 min, and the thickness of the interfacial reaction layer is less than 5 μm.
Research status and development of powder metallurgy porous tungsten
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Abstract(57) PDF(10)
Abstract:
Porous tungsten is composed of tungsten skeleton and its high proportion of internal pores, which combines the excellent characteristics of refractory metal tungsten and porous materials. It is widely used in aviation, electronics, high temperature and other fields due to its excellent high temperature resistance, corrosion resistance, high specific surface area and high permeability. Currently, the main application of porous tungsten is to utilize the functions of pore connectivity, filling, storage and filtration on the basis of the intrinsic characteristics of metal tungsten. Therefore, the key to prepare high-performance porous tungsten and further broaden its application lies in obtaining stable and controllable pores. This paper focuses on the control of porosity characteristics in the preparation process. Firstly, the crucial role of porosity characteristics in the main applications of porous tungsten is elaborated. Then, the effects of powder characteristics, forming methods and sintering system on the pore characteristics of porous tungsten are summarized. Finally, the future research directions and development trend of porous tungsten have been pointed out.
Preparation of ZrC/Mo-Si metal silicides composite nano powder by direcrt electrochemical process in molten salt
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Abstract(35) PDF(4)
Abstract:
ZrC/Mo-Si metal silicide composites are normally prepared by the sintering techniques at high temperature (1750~2100 ℃) or high pressure using ZrC and Mo-Si metal silicide powders as raw materials. However, these methods typically suffer from high cost, high energy consumption and high resource consumption. It is highly desired to develop a simple, low energy consuming and low-cost preparation method. In this work, ZrC/Mo-Si metal silicide composite nano-powder was prepared from a ZrSiO4/ MoO3/C mixture through a one-pot electrolytic process in molten salt. The effects of the preparation process of solid cathode, carbon content and type of carbon source on the electrochemical synthesis of ZrC/Mo-Si metal silicide composite nano-powder were investigated. The results show that ZrC/Mo-Si metal silicide composite nano-powder was prepared by electrochemical reduction at 800 ℃ under 3.1 V for 15 h in CaCl2-NaCl eutectic molten salt, and it was composed of nearly spherical particles with particle size less than 50 nm. It was found that the carbon powder with amorphous structure and relatively smaller particle size is more suitable as carbon source for electrochemical synthesis of ZrC/Mo-Si metal silicide composites. Moreover, the ratio of ZrC and metal silicide phases, as well as the composition of metal silicide in the final product can be controlled by adjusting the amount of carbon in the original material.
Study on the properties of Fe-Si-B-Cr-C amorphous alloy powders with different particle sizes prepared by air-water combination atomization
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Abstract(61) PDF(24)
Abstract:
FeSiBCrC amorphous alloy powder with 6 particle sizes were prepared by a new industrial gas-water atomization and the amorphous magnetic core were prepared, which study the effects of particle size and annealing temperature on the properties of the magnetic core. The results show that the FeSiBCrC alloy powder with particle size D50≤25 μm are all amorphous, and the width of the supercooled liquid phase region ΔT can reach 40 ℃, which indicates that the FeSiBCrC alloy powder has strong amorphous formation ability. The saturation magnetization Ms and coercivity Hc of amorphous powders increase with the increase of particle size. The Ms value of A5（D50=5 μm）is 144.6 emu?g-1, and the Hc value is 1.8 Oe. However, the Ms value of A30 （D50=30 μm）is 152.6 emu?g-1 and the Hc increases to 9.8 Oe. The permeability μe of amorphous magnetic cores with different sizes has good stability in the frequency range of 0.1~600 kHz, and the fine powder phase is better than the coarse powder. The magnetic loss Pc of all amorphous magnetic cores increases with the increase of frequency. The finer the particle size, the more obvious the effect of annealing on reducing the magnetic loss Pc, in which the A5 (D50=5 μm) is decreased by about 84%, while the A30 (D50=30 μm) is only decreased by about 30%. After annealing at 500 ℃, the A5 (D50=5 μm) magnetic loss Pc reaches a minimum value of 578 mW?cm-3.
Effect of laser power on microstructure and wear properties of laser cladding Stellite 6 alloy coating
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Abstract(76) PDF(17)
Abstract:
Stellite 6 alloy coating was prepared on 0Cr17Ni4Cu4Nb stainless steel by laser cladding technology. The microstructure of the coating was characterized by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and confocal laser scanning microscopy (CLSM). The hardness and wear resistance of the sample were tested. The coatings prepared with different laser power parameters had no obvious defects such as pores and cracks. The coating of all samples had good metallurgical bonding with the substrate. Therefore, all 5 laser powers were reasonable process parameters. The microstructure of the coatings mainly consisted of coarse columnar dendrite at the bottom, coarse dendritic crystals at the middle, and fine equiaxed dendrite at the top. The hardness of the coating (420~510 HV) was significantly higher than that of the substrate (206 HV), and the hardness gradually decreased from the top of the coating to the substrate. The sample with a laser power of 1400 W exhibited the smallest and most uniform microstructure, while there were more hard phases (carbides) between dendrites. Therefore, the 1400 W sample exhibited the highest hardness. After wear experiment testing, all sample surfaces showed parallel furrows along the sliding direction, without obvious accumulation of debris, which belongs to the abrasive wear mechanism. The sample with a laser power of 1400 W had the lowest friction coefficient (0.353) and wear rate (0.954 m3sN-1), while the 1400 W sample had the narrowest wear scar width (928.463 μm) and the minimum depth of wear marks (45.087 μm), exhibiting the best wear resistance.
Research Progress On Composition Design And Preparation Technology of ODS Steels For Advanced Nuclear Energy System
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Abstract(106) PDF(25)
Abstract:
Developing the Gen IV nuclear energy system with higher safety and economy isthe focus ofcurrent research as the nuclear energy is a clean energy. To develop the materials with excellent comprehensive properties has become the urgent problem as the traditional zirconium alloy was unable to adapt the harsh service environment ofthe Gen IV nuclear energy system. Oxide dispersion strengthened (ODS) steel is considered to be an important candidate clad materialfor the Gen IV energy system owning to its excellent comprehensive properties. Reasonable composition design and unique microstructureareimportant reasons for the excellent properties of ODS steel. The high number density of dispersed oxide particles greatly improves the high temperature mechanical properties and irradiation resistance of the alloy. Although a lot of research work has been carried out around the world on the composition design-property-preparation process of ODS steels, therestillexists challenges in mass production that limit the engineering applications of ODS steels. This paper summarizes and analyzes the research work on microstructure, composition design and preparation technology of ODS steels in domestic and international, and summarizes and outlooks the application prospects and current problems of ODS steels in the field of nuclear energy, so as to provide reference for the development of nuclear-grade ODS steels.
Research Progress in Equipment and Processes of Electron Beam Powder Bed Fusion Additive Manufacturing
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Abstract(61) PDF(16)
Abstract:
Electron beam powder bed fusion (EB-PBF), as an important meta additive manufacturing technology, has outstanding characteristics such as high power, high energy utilization, fast scanning speed, low forming stress, and vacuum environment forming，and attracts increasing attention in academics and industry. In recent years, many breakthroughs have been made for EB-PBF system and process.The problems that have long plagued the innovative development and application of this technology, such as small forming dimensions and short life of cathode, have been preliminary solved, and multiple new forming processes and online monitoring technologies for forming quality have emerged, the additive manufacturing of complex components made of high melting point, high activity,brittle and difficult to machine metal materials has shown broader application prospects. This article reviews the new developments in EB-PBF additive manufacturing technology both domestically and internationally from three aspects: system technology,forming process, and process monitoring. It also analyzes and prospects its development trends, technological challenges, and application prospects.
Extrusion Molding 3D Printing Bionic Bone Implantation Titanium Alloy Scaffold Preparation Process and Performance Research
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Abstract(56) PDF(8)
Abstract:
Titanium alloy scaffolds have good mechanical properties and can mimic the structure and properties of human bones, making them ideal materials for bionic bone implant applications. In this paper, the preparation process and mechanical properties of extrusion molding 3D printed Ti6Al4V titanium alloy scaffolds are systematically investigated. The preparation of titanium alloy scaffolds using poly(vinyl alcohol) (PVA) hydrogel is introduced, which can obtain a porous structure with uniform distribution and high interconnectivity. The influence laws of slurry PVA content and sintering temperature on the preparation process were investigated, and the relationship between the porosity and mechanical properties of titanium alloy scaffolds was analyzed. The mechanical properties and microstructure of the titanium alloy scaffolds were tested and analyzed using a universal testing machine and a scanning electron microscope, respectively. The results showed that the preparation process was optimal when the slurry PVA content was 15 wt%. The degreasing and sintering temperatures were set at 360 °C and 1300 °C, respectively. The titanium alloy scaffolds with a porosity of 59.8% exhibited mechanical properties matching those of human bones to avoid stress-masking effect.
Fe2Ni metal powder injection molding deformation optimization
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Abstract(67) PDF(8)
Abstract:
The issue of product deformation during the upper jaw production in Metal Power Injection?Moulding?(MIM) technology stemmed from poor binding material adhesion and excessive shear heat generation, leading to uneven metal powder distribution. To address this problem, a series of melt index experiments were conducted using three different materials with varying powder content. These experiments assessed fluidity and coupling characteristics. Utilizing?the Taguchi method, extreme deviation analysis, and analysis of variance, the?optimization?of three critical process parameters—gate area,?mould?temperature, and injection temperature—was pursued. The objective was to investigate how these process parameters interacted and affected shear stress. Ultimately, the most effective combination was determined to be a powder loading of 62.5 vol% alongside the following process parameters: a gate area of 23.984 cm2, a?mould?temperature of 69.854 ℃, and an injection temperature of 194.323 ℃. Validation analysis using Moldex 3D software confirmed that this set of conditions resulted in the lowest shear stress within the product and the highest level of powder uniformity. Consequently, this?optimized process configuration successfully alleviated the deformation issue in the final product.
The effect of ball milling time on the particle size and morphology of fine copper powder prepared by ball milling method
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Abstract(94) PDF(13)
Abstract:
Through the control of ball milling time, the influence of ball milling time on the particle size distribution and powder morphology of fine copper powder was investigated, and the suitable ball milling time parameters were determined. The results show that before the ball milling time is 20 h, the particle size distribution index of copper powder continues to decrease with the increase of ball milling time, and the agglomeration of copper powder is not obvious. After that, with the increase of ball milling time, the agglomeration of ball milled copper powder was obvious, and the uniformity of ball milled copper powder decreased. Comprehensive analysis, when the ball milling time is set to 20 h, the particle size distribution, phase analysis and appearance of the ball milled copper powder are the best. At this time, the uniformity of the ball milled copper powder is improved, the surface of the powder is relatively flat, the diameter distance Dδ reaches the minimum value of 1.723, the specific surface area is 0.796 m2.g-1, and the median diameter D ( 0.50 ) is 9.97 μm.
Oxidation behavior of molybdenum alloy coatings at 1200℃
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Abstract(55) PDF(3)
Abstract:
Three coatings of which containing borosilicate glass and being doped with MoSi2 and aluminum powder were prepared on the surface of TZC molybdenum alloy using a coating method, and the oxidation behavior of the coatings at 1200 ℃ was studied using heating furnace, X-ray diffraction analyzer, and scanning electron microscope. The results show that the aluminum powder modified coating has good protective performance within 1 hour, and the oxidation resistance after 2 hours is 69% higher than that without coating protection. Research has found that the cross-section of borosilicate glass and MoSi2 doped coating is mainly composed of a loose structure with alternating distribution of MoO3 and TiO2 after oxidation, while the addition of Al powder changes the phase composition of the oxide film, forming a three-layer structure of outer aluminum silicate, middle cerium titanium oxide, and inner TiO2 and molybdenum silicon compound, making it have excellent antioxidant effect.
Study on Fe ion irradiation hardening of additive manufacturing 316 stainless steel
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Abstract(50) PDF(3)
Abstract:
316 stainless steel was fabricated through selective laser melting (SLM) additive manufacturing and compared to traditionally manufactured counterparts. The microstructure and performance characteristics were assessed using metallographic microscopy, scanning electron microscopy, X-ray diffraction, and Vickers hardness testing. To investigate irradiation-induced hardening effects, 3.5 MeV Fe ions irradiation was carried in two types of 316 stainless steel at room temperature. The results indicate that the additive manufacturing 316 stainless steel displays a characteristic columnar crystal structure with a single austenite γ phase, accompanied by a high-density subgrain-like cell wall structure and the hardness exhibits anisotropy between the scanning and deposition plane. Irradiation hardening effects are observed on two types of 316 stainless steel after Fe ions irradiation, and hardening rate of the 316 stainless steel produced through additive manufacturing was found to be less significant than that of traditionally manufactured steel. Furthermore, there is also anisotropy in irradiation hardening.
Study on Preparation of Mo–Ni alloy with spark plasma sintering
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Abstract(42) PDF(2)
Abstract:
Mo-Ni alloy was prepared by spark plasma sintering. The effects of sintering temperature, pressure, holding time and heating rate on the relative density of Mo-Ni alloy were studied. The relative density, microstructure and phase of Mo-Ni alloy were characterized by SEM, XRD and EBSD. The densification process of Mo-Ni alloy sintered by spark plasma was analyzed.The results show that, Sintering temperature and pressure are the main factors affecting the relative density of Mo-Ni alloy; The maximum relative density is 99.10%, and the average grain size is less than 10μm;The local high-speed diffusion of Mo and Ni is the main reason for promoting the densification of Mo-Ni alloy;The phase of sintered Mo-Ni alloy is mainly composed of Mo and Mo-Ni mesophase,and Mo particles are evenly distributed in the network structure formed by Mo-Ni mesophase;The average rockwell hardness value is 72.The content of additive Ni% does not change much before and after sintering.
Research on the Preparation of High-Quality Silicon Nitride Ceramic Powder by Direct Nitriding Method
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Abstract(128) PDF(24)
Abstract:
High-quality silicon nitride ceramic powder was prepared by direct nitriding method, using silica powder as raw material, and the effects of nitriding temperature, heating rate, silica fume particle size and diluent dosage on the powder were explored. The raw silicon fume D50 was 275.36 nm, without Si3N4 diluent, when the reaction temperature was 1400 ℃, the heating rate was controlled at 5 ℃/min at 1100~1400 ℃, the silicon fume was completely nitrided, and spherical silicon nitride materials with uniform particle size (particle size range of 396~458 nm) were prepared. The material has good dispersion, and the mass fraction of the α phase is as high as 95.02%. The results showed that the heating rate was the key factor controlling the reaction process. when the heating rate was too fast or too slow, the conversion degree of silicon nitride from α phase to β phase exceeded the internal reaction degree, and the silica fume reaction was incomplete. The addition of Si3N4 diluent reduced the nitriding temperature. The research results provide a technical basis for the optimization of industrial production process of silicon nitride ceramic powder.
Research progress in Metal injection molding of aluminum alloy
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Abstract(134) PDF(26)
Abstract:
相应需要进行修改 Aluminum and its alloys are distinguished by their low density, resistance to corrosion, lightweight nature, high specific strength, and impressive thermal conductivity. Their widespread use as essential structural elements for weight reduction signifies their substantial potential in various sectors, including transportation, electronics, healthcare, and the chemical industry.Powder Injection Molding (PIM) of aluminum alloys facilitates the low-cost fabrication of intricately structured, fine aluminum alloy products. This technique offers the benefits of uniform material distribution, precise dimensional accuracy, and heightened raw material utilization, thereby playing 投稿日期:2023-08-03 a critical role in advancing the industrialization of injection-molded aluminum alloy components and expediting their incorporation into electronics and medical devices.This paper presents an overview of the current advancements in aluminum alloy injection molding, and evaluates the preparation prerequisites of feedstock for this process, with an emphasis on binder component design, degreasing strategies, and their atmospheric sintering behavior. We also delve into the role of alloying elements in the sintering densification mechanism. Furthermore, this paper identifies urgent issues and future development directions in the field of aluminum alloy powder injection molding.
Study on pressing process of Mo-47.5wt%Re alloy prepared by powder metallurgy
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Abstract(55) PDF(7)
Abstract:
The difference of cold isostatic pressing between Mo-47.5wt%Re alloy powder prepared by ball milling and plasma spheroidized was compared and analyzed. The compression parameters were fitted using the double natural logarithm equation of "Huang Peiyun". The results show that, when cold isostatic pressing was carried out in the mold with large Length-diameter ratio, the axial shrinkage of the compact was greater than that of the radial shrinkage after the ball grinding and plasma spheroidized molybdenum-rhenium alloy powder were pressed. Pressed billet of the plasma spheroidization alloy powder is complete and uncracked, its density change less along the axial direction, and the centre density is slightly lower than the density at both ends. While the billet pressd with ball milling alloy powder is broken like bamboo joint, its density varies greatly along the axial direction, and the centre density is significantly lower than the density at both ends. The relationship between pressing pressure and green density was analyzed by Huang Peiyun's "double logarithmic pressing theory". It shows that the m value of plasma spheroidization alloy powder is slightly higher than that of ball milling alloy powder, while its M value lower than that of ball milling alloy powder, which means the hardening tendency of plasma spheroidization alloy powder is greater, and it is easier to press than ball milling alloy powder.
Effects of micro-TiC on microstructure and mechanical properties of selective laser melted Inconel 625 alloy
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Abstract(66) PDF(12)
Abstract:
In order to further improve the mechanical properties of Inconel 625 alloy materials, SLM In625-xTiC alloy materials were prepared by selective laser melting (SLM) technology, and the influence mechanism of TiC content on microstructure and mechanical properties of SLM In625-xTiC alloy was investigated. The microstructure, elemental distribution and mechanical properties of SLM In625-xTiC alloy specimens were comparatively analyzed by combining advanced material characterization means. The results show that the SLM In625-xTiC material is mainly composed of γ-Ni, TiC and Laves (Cr2Nb) phases, and with the increase of TiC content, the microstructure is also gradually transformed from the morphology of columnar dendritic crystals in the middle of the melting channel, which is dominated by isometric crystals at the junction of the melting channel, to the organizational morphology consisting of sub-structures, such as cytosolic isometric crystals, and it also contributes to the hardness of SLM In625-6 TiC alloy. The hardness of the alloy increased from 335.1±12.51 HV0.2 without TiC to 525.3±15.13 HV0.2, and the tensile strength increased from 975.96±18.33 MPa to 1440.31±22.33 MPa, but the total elongation decreased sharply from 30.0±0.56 % to 3.2±0.98 %. In conclusion, the reinforcement of In625 alloy with micron TiC particles by SLM method is one of the effective methods to improve its mechanical properties.
Preparation of ultrafine Cu-20W composite powder by sol-gel with hydrogen reduction technology and its sintering behavior
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Abstract(67) PDF(15)
Abstract:
In this paper, Cu-20wt.% (Cu-20W) ultrafine composite powders were prepared by a combination of sol-gel with hydrogen reduction method using ammonium metatungstate and copper nitrate as raw materials, and Cu-20W samples were obtained by pressing and sintering. The morphology and particle size of the powders were characterized and the effect of temperatures on the structure and properties of the Cu-20W samples were investigated. The results show that the Cu-20W composite powders with an average particle size of less than 100 nm by a combination of sol-gel with hydrogen reduction method; with the increase of sintering temperature, the physical and mechanical properties of Cu-20W samples are improved. The relative density of the samples sintered at 1080 °C is 97.20 %, the electrical conductivity (IACS), thermal conductivity, Vickers hardness and tensile strength are respectively reached 91.73 %, 351.52 W·m-1·K-1, 96.1 HV and 431.03 MPa; the CTE values of the Cu-20W samples ranged from 14.871×10-6·K-1 and 17.422×10-6·K-1 in the temperature range of 100 ℃ to 400 ℃.
Study on heat treatment properties of Mo-Re alloy strengthened by La2O3
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Abstract(60) PDF(8)
Abstract:
Molybdenum rhenium alloy is a solid solution strengthening alloy with high melting point and low expansion coefficient, and the addition of rare earth oxides can refine the grains and play a role in dispersion strengthening. In this paper, the microstructure and room temperature tensile fracture morphology of molybdenum rhenium alloy (Mo-14 % Re) and molybdenum rhenium lanthanum alloy sheet with 0.8 % (mass fraction) La2O3 were observed at different annealing temperatures, and the Vickers hardness and room temperature tensile properties were compared. The results show that with the increase of annealing temperature, the recrystallization temperature of molybdenum rhenium lanthanum alloy increases from 1200 °C to about 1400 °C compared with that of molybdenum rhenium alloy. The hardness and strength of molybdenum rhenium alloy and molybdenum rhenium lanthanum alloy gradually decrease, while the elongation of molybdenum rhenium lanthanum alloy gradually increases, up to 27.5 %.
Research on the preparation and properties of the P-type Bi2Te3 based material with high preferred orientation
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Abstract(97) PDF(20)
Abstract:
In order to solve problems of low preferred orientation, poor mechanical strength and low thermoelectric properties of the (00l) face of the P-type Bi2Te3-based material, an alloy ingot with very good orientation was produced by magnetic levitation melting technology which is rapid induction melting and casting into a water-cooled copper with Bi0.4Sb1.6Te3+3wt.%Te crystal bar as raw materials. SEM and XRD pattern of casted ingots, alloy powders, hot-pressed sintered blocks were done, and the effect of powder particle size on the electrical properties of sintered block were studied. The results show that the powder after quenching, crushing and screening is highly oriented along the (00l) crystal face. The zone melting N-type matches the conventional 127 pair 4 cm*4 cm refrigeration TEC, and the maximum temperature difference of the model TEC1-12706 device can reach 70℃,which provides a direction for the preparation of high-performance Bi2Te3-based thermoelectric materials.
Research Progress of High-Speed Steel Prepared by Powder Metallurgy
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Abstract(98) PDF(21)
Abstract:
As a tooling material with high strength and toughness, HSS is widely used in the manufacture of various cutting tools, moulds, rolls, wear parts, etc. By producing HSS through powder metallurgy, not only can the problem of tissue segregation be effectively avoided, but the mechanical properties and service life of the material are also improved. This paper outlines the development of powder metallurgy HSS, including the powder making process, forming process and the current situation at home and abroad, points out the current problems of powder metallurgy HSS, and outlooks its future development trend.
Numerical calculation of sintering of 316L part printed by Binder JettingAdditive Manufacturing
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Abstract(52) PDF(6)
Abstract:
The purpose of this paper is to investigate and predict the deformation behavior during the sintering of metal parts for binder jet additive manufacturing (BJAM). A viscoplastic constitutive model is developed. The model is based on continuum media mechanics and Newtonian viscosity, and integrates the effects of grain growth factor and frictional contact between the part and substrate under gravity on sintering deformation. The parameters in the present constitutive model depend on grain size, relative density and temperature. Write umat subroutine in Abaqus using this constitutive model to simulate the sintering behavior, and the widely used 316L powder was selected for experiments. The calculated values of shrinkage deformation, etc. were compared with the experimental data, and the results showed that the constitutive model has good prediction.
Effects of pressing pressure on the physical and electrical contact properties of silver based contact materials
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Abstract(119) PDF(16)
Abstract:
The Ag/SnO2, Ag/ZnO, Ag/Ni and Ag/W materials were prepared by powder metallurgy method. The effects of pressing pressure on the physical and electrical contact properties of different silver-based contact materials were systematically studied. The results showed that the relative densities of the Ag/SnO2 and Ag/ZnO materials significantly increased with the increase of pressing pressure. While, the densities of Ag/Ni and Ag/W alloys obviously decreased. When pressing pressure reached 600 MPa, the electrical conductivity of the Ag/SnO2 material could be increased from 35.2 to 52.6 %IACS. The electrical contact properties of the Ag based contact materials were greatly affected by pressing pressure. The Ag/SnO2 and Ag/ZnO materials prepared under 600 MPa showed the lower arcing energy and contact resistance. Especially, the Ag/ZnO material exhibited the best arc erosion resistance, and the contact resistance was less affected by pressing pressure. Although the conductivity of Ag/W alloy was up to 93% IACS, the mass loss of its anode was larger after arc erosion. The surface of cathode was rough and the obvious cracks were generated. In addition, the contact resistance was greatly affected by pressing pressure. In contrast, the mass loss of Ag/Ni alloy was lower and mainly occurred at cathode, resulting in a good arc erosion resistance.
Research progress of additive manufacturing technology in diamond tool preparation
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Abstract(64) PDF(9)
Abstract:
Due to the high hardness and excellent wear resistance, diamond is widely used in the preparation of cutting and other machining tools . As compared to traditional manufacturing technology, additive manufacturing can fundamentally solve the problems of innovative design and efficient fabrication for complex structural components, and is a potential effective method for preparation of high-performance diamond tool. This article introduces the basic principles and characteristics of major additive manufacturing technologies such as Selective Laser Sintering (SLS), Selective Laser Melting (SLM), Stereo Lightgrapy Apparatus (SLA), Direct Ink Writing (DIW) and Fused Deposition Modeling (FDM). The applicability of different additive manufacturing technologies in the preparation of diamond grinding wheels, diamond drill bits and diamond saw blade tools as well as the performance of manufactured tool are analyzed. Finally, the typical problem in the deposition process of additive manufactured diamond tools and the corresponding solution idea are summarized and provided, respectively.
Effects of mechanical milling on microstructure and tensile properties of powder metallurgy CoCrFeMnNi high-entropy alloys produced by spark plasma sintering
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Abstract(67) PDF(20)
Abstract:
Powder metallurgy can produce high-performance high-entropy alloys with fine and homogenous microstructure. In the present work, CoCrFeMnNi high-entropy alloys with nearly full density were fabricated by spark plasma sintering (SPS) process. The effects of mechanical milling of pre-alloyed powder on microstructure and tensile properties of CoCrFeMnNi powder compacts were investigated. The results showed that the sphericity of the pre-alloyed powder decreases with the increasing milling time. The phase composition of as-SPSed alloy presents a single FCC structure, and the grain size decreases with the increasing pellet ratio and mechanical milling time. Compared with the power compact without mechanical milling, the yield strength of the as-SPSed alloy increases with the increasing mechanical milling energy, which reaches the highest value when the pellet ratio is 7.5:1 and the mechanical milling time is 100 h. increasing by about 19%. The increment of yield strength (about 19%) is mainly due to the fine grain strengthening. The ultimate tensile strength tends to firstly increase and then decrease, which reaches the highest value when the pellet ratio is 7.5:1 and the mechanical milling time is 30 h, increasing by about 12%.
Fe50Mn30Co10Cr10-xNbC high-entropy alloy composites prepared by SPS technology and characterization of properties
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Abstract(69) PDF(8)
Abstract:
In this paper, Fe50Mn30Co10Cr10-xNbC (x = 0, 2, 5, and 10 wt.%) high-entropy alloy composites were prepared by Spark Plasma Sintering (SPS) and analyzed by optical microscopy, X-ray diffractometer, scanning electron microscope, microhardness tester and electrochemical workstation. The microstructure, hardness and corrosion resistance were analyzed using optical microscopy, X-ray diffraction, scanning electron microscopy, microhardness tester and electrochemical workstation. The results show that the carbon in the graphene spacer diffuses into the Fe50Mn30Co10Cr10 high-entropy alloy matrix during the SPS sintering process, which inhibits the formation of the dense hexagonal (HCP) phase and makes it consist of a single-sided centered cubic structure (FCC). In addition, the diffused carbon forms a compound of M23C6 ((Fe, Co, Mn, Cr)23C6) at the grain boundaries with Fe, Co and Cr in the alloy of the matrix. the addition of NbC increases the number of nucleation plasmas and refines the grains; the hardness is significantly increased with the increase of NbC content, with the highest value of HV 463 for the sample containing 10 wt.% NbC; The wear resistance first increased and then decreased, where the high entropy alloy with 2 wt.% NbC added had the best wear resistance with a low wear amount of 0.2479 mg; the corrosion resistance first became better and then worse, and the curves of polarization curves and impedance spectra showed that the samples with 5 wt.% NbC added had better corrosion resistance. The corrosion resistance is closely related to the composition and distribution of the compounds at the grain boundaries. When a small amount of NbC is added, the grain boundary precipitation of elemental Cr is suppressed and the corrosion resistance is improved; however, with the enhancement of the continuity of coarse NbC particles precipitating on the grain boundaries and the increase of the carbide content of Cr-rich phase, the corrosion resistance deteriorates rapidly.
Preparation and characterization of Pd/porous Ta/Ta composite membrane
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Abstract(60) PDF(2)
Abstract:
In order to promote the application of metal tantalum(Ta) in the fields of electronics, military, medical devices, aerospace and chemical engineering, the porous Tamembrane was prepared on the surface of Ta foil by the process of spraying combine sintering.Subsequently, the composite membrane(Pd/porousTa/Ta) was prepared by electroless Pd plating processeswhich using porous Ta/Ta as the composite substrate. The surface morphology shows that the sintering temperature has a significant impact on the structure of porous Tamembrane. The porous Ta membrane with well-developed sintering neck can be obtained after sintering at 1700oC for 2 hours.The electroless plating time has a significant effect on the Pdmembrane on the surface of porous Tamembrane. Due to the complex surface structure of porous Tamembrane,causedit was difficult to obtain uniform and dense Pdmembrane on the surface of porous Tamembrane..
Spherical FeSiCr powder prepared by improved combination atomization process
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Abstract(82) PDF(15)
Abstract:
In order to study the effect of morphology on powder properties, the conventional combined atomization smelting process is improved and optimized. The role of primary atomization stage is further strengthened, the time of droplet spheroidization is prolonged, and the morphology of powder is improved. Spherical powder samples with different particle sizes prepared by the improved combination atomization process and compared with the conventional combination atomization. The results show that the powder prepared by the improved atomization process has the characteristics of good morphology, small specific surface area and low oxygen content. At the same time, the permeability of the improved atomized powder is lower than that of the conventional atomized powder, but the DC bias ability of the magnetic core is significantly improved, and the hysteresis loss and eddy current loss are significantly reduced. ?
Influence on mechanical properties of 3D printing porous tungsten by control shape and size of porous
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Abstract(56) PDF(7)
Abstract:
In this paper, porous tungsten with two pore shapes, cube and triangular pyramid, were designed. The finite element analysis shows that when point, line, and surface loads are applied respectively, the stress on the cube and triangular pyramid skeleton units is uneven. When the skeleton unit is subjected to plane and line loads respectively, the stress at the supported struts is relatively small, while the stress at the unsupported struts is relatively large, causing a large amount of deformation. When the skeleton unit is subjected to a point load, its stress and deformation are both maximum at the loading point. Two types of porous tungsten with high porosity were fabricated by selective laser melting (SLM) technique, and the effects of pore shape and size on mechanical properties were investigated. The results show that the macrostructure of both these skeleton structure is not significantly different from the designed structure. Because of the hanging and sticky powders on the struts, the porosity is lower than the designed value. The tensile strength of cube skeleton with 50% and 80% porosity is 127.4 MPa and 55.8 MPa, the compressive strength is 667.1 MPa and 213 MPa, the impact toughness is 6.7641 J·cm-2 and 4.4924 J·cm-2, respectively. In addition, both have similar hardness. The compressive strength of the triangular pyramid skeleton with the same designed porosity is 231.1 MPa and 65.3 MPa, the impact toughness is 2.03 J·cm-2, and has the same hardness as the cube skeleton. The tensile and compressive fracture morphology of cube and triangular porous tungsten shows typical quasi-cleavage brittle fracture.
Study on the effect of melt tip taper angle on atomization process in gas atomization
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Abstract(103) PDF(19)
Abstract:
The spherical powder for 3D printing prepared by gas atomization has fine particle size and high sphericity, which is suitable for large-scale industrial production. Atomizing nozzle is the core component of the gas atomization process. Its structural parameters, especially the melt tip taper angle of the delivery tube, have a great impact on the gas atomization results. Meanwhile, changing the taper angle of the melt tip is more effective and economical than changing the atomization process parameters such as gas pressure and temperature. In this paper, the computational fluid dynamics (CFD) method was used to simulate the internal flow field variation in the spray chamber with different melt tip taper angles. The commercial CFD software FLUENT is used to calculate and visualize the complex multiphase flow process in the closed spray chamber with high temperature and high pressure. The results show that the direction of air flow can be changed by changing the melt tip taper angle (16°, 22°, 28°, 34°, 40°, and 46°). With the change of the taper angle, the stagnation point position, the stagnation pressure and the suction pressure in the single-phase flow field show regular characteristics. The influence of various factors in the single phase flow field on the melt breaking effect was analyzed. Secondly, the Volume of Fluid (VOF) model was used to simulate the primary atomization process. The results show that the mass median diameter (MMD) of the primary atomization also varies with the change of the melt tip taper angle. The droplet size distribution after primary atomization can be controlled by changing the melt tip taper angle. In the case studied, the minimum MMD was 304 μm when the melt tip taper angle was 34°.
Microstructure and mechanical properties of selective electron beam melting W-0.51wt%B alloy
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Abstract(77) PDF(9)
Abstract:
In view of the coarseness of grains in microstructure of pure tungsten after selective electron beam melting (SEBM), B was selected as the grain refinement element. Besides, the influence of forming process parameters on the densification, microstructure and mechanical properties of W-B alloy was explored. It is found that when the forming process parameters are I=15 mA, v=300 mm·s-1 and E=1200 J·mm-3, the density of W-B alloy samples is the highest, and the pores and unfused powders are the least, the microcracks were basically suppressed. The constitutional undercooling caused by the introduction of element B effectively refined the grain size of W formed by SEBM, and the microstructure changed from coarse columnar crystal to fine columnar dendrites with an average size of about 8.26 μm. The highest hardness of W-B alloy is 672 HV, and the highest ultimate compressive strength is 1598 MPa. The fracture mechanism is mainly cleavage fracture.
Preparation of TiB2-Co-Cr-W composite powder by high energy ball milling
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Abstract(71) PDF(13)
Abstract:
The TiB2-Co-Cr-W composite powder was prepared by mechanical alloying using a high-energy ball milling process. The effects of ball milling time, ball material ratio and ball milling speed on the particle size of the composite powder were investigated by means of orthogonal tests. The effects of ball milling time, ball material ratio and ball milling speed on the refinement process and alloying process were investigated by XRD, SEM and TEM, respectively, TiB2-Co-Cr-W cermet composites were prepared by pressureless sintering. The results show that the ball milling time has the most significant effect on the refinement of the powder particles, while the ball material ratio has less influence on it. The optimum ball milling process was: ball-to-material ratio of 10:1, ball milling speed of 150 r/min and ball milling time of 48 h. The TiB2-Co-Cr-W composite powder prepared under the optimum ball milling process showed obvious alloying effects, with the TiB2 diffraction peak broadening, peak intensity decreasing and lattice constant decreasing, and some metal elements solidly dissolving into the TiB2 crystal structure, forming solid solution and amorphous material. Finally, the relative density of TiB2-Co-Cr-W composites obtained by pressureless sintering at 1600℃ for 1 h reached 98.8%, and the opening of the porosity is 0.1%.
Effects of pore-forming agent on microstructure and properties of biomedical porous Ti/16Mg composites
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Abstract(80) PDF(35)
Abstract:
High strength titanium alloys can be prepared by powder metallurgy process, but the titanium alloy still has some problems such as high elastic modulus and unsuitable pore properties for bone growth. In this paper, the biomedical porous Ti/16Mg composite material with elastic modulus close to that of human bone and strength meeting the requirements of human implants was prepared by powder metallurgy combined with microwave sintering method. The effects of particle size and addition amount of pore-making agent NH4HCO3 on microstructure, mechanical properties and corrosion resistance of the composites were investigated by scanning electron microscopy, X-ray diffraction, metallography, compression test and corrosion resistance test. The results show that NH4HCO3 has no significant effect on the phase composition of porous Ti/16Mg composites. The pore size of the sample increases with the increase of NH4HCO3 particle size, and the porosity of the sample increases from 16.64% to 33.09% with the increase of NH4HCO3 addition. When the particle size of NH4HCO3 is 165-198 μm and the addition amount is 18wt.%, the elastic modulus of the sample is 6.49 GPa and the compressive strength is 115 MPa, which can meet the mechanical property requirements of human implants. Different particle sizes of NH4HCO3 have little effect on the corrosion resistance of the composites. With the same particle size, the corrosion resistance of the composite decreases slightly and the polarization resistance decreases from 574.528Ω?cm-2 to 139.236Ω?cm-2 with the addition of NH4HCO3 increasing from 0 to 24wt.%.
Controllable preparation and regulation mechanism of ultrafine spherical cobalt powder
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Abstract(149) PDF(22)
Abstract:
Using CoCl2·6H2O and NH4HCO3 as raw materials, the CoCO3 precursor with fine, uniform and controllable particle size was prepared by liquid-phase precipitation method, and then ultrafine spherical cobalt powder was prepared by calcination-hydrogen reduction. Scanning electron microscope (SEM), X-ray diffractometer (XRD) and simultaneous thermal analysis (DSC-TG) were used to characterize the microscopic morphology, phase and weight loss ratio of the powder obtained at each stage, respectively. The influence of stirring time and reaction temperature on the particle size and morphology of CoCO3 in the liquid-phase precipitation method was analyzed; the influence of hydrogen reduction process on the phase, particle size and morphology of the reduction product was analyzed. The results show that the nucleation rate of CoCO3 will increase with the increase of stirring time and reaction temperature, and then the average particle size of CoCO3 will decrease. CoCO3 with high sphericity and an average particle size of 0.96 μm. In the process of hydrogen reduction of Co3O4, with the prolongation of hydrogen reduction time and the increase of temperature, the particle size of cobalt powder becomes larger; when the hydrogen reduction temperature is 400 ℃ and the time is 45 min, the average particle size of cobalt
Effect of Ultrasonic Surface Rolling Process Microstructure and Properties of Titanium Hydride Sintered Pure Titanium
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Abstract(140) PDF(29)
Abstract:
In this work, a titanium prepared by sintered titanium hydride was treated by ultrasonic surface rolling process (USRP), and effects of the plastic deformation on microstructure evolution and properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM).Results demonstrated that a gradient microstructure was produced by the USRP with the static load of 600 N, and the average thickness of the deformation layer was about 400 μm. In particular, the outermost layer of the deformed microstructure displayed an equiaxed nanocrystals, and the average grain size of the fine grains was about 100 nm. Improvement of surface roughness, grain refinement and high surface compressive residual stress caused by rolling synergistically help to form a dense and stable passive film on the deformation layer, which could improve the corrosion resistance effectively. In addition, taking advantages of the microstructure evolution, the ultimate tensile strength and yield strength were 640.57 MPa and 485.29 MPa, increased by 32.43 % and 27.57 % respectively. Meanwhile, the surface hardness was increased by 36% for the USRP treated titanium alloy.However, the introduction of deformation layer made a decrease of uniform elongation, while the fracture morphology indicated a ductile failure.
Microstructure and mechanical properties of FeCrCoMnNi matrix composite reinforced by TiC particle
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Abstract(99) PDF(25)
Abstract:
FeCrCoMnNi matrix composites reinforced by TiC particle were prepared by mechanical ball milling and spark plasma sintering. Effects of TiC content and sintering temperature on the microstructure and mechanical properties were evaluated. The results show that the composites are composed of FCC matrix and TiC and Cr23C6 carbide reinforcement, and the amount of Cr23C6, formed by the reaction between Cr and C, increased with the content of added TiC. The reinforcement distributed relatively uniform in the composites for the samples fabricated at 1000 ℃, when the TiC content ranges between 1 wt.% to 9 wt.%. The sintering temperature has a significant effect on the microstructure and mechanical properties, the samples sintered at 1000 ℃ or 1050 ℃ have a relatively uniform microstructure and exhibit better mechanical properties. The hardness and room temperature yield strength of sample with 7 wt.% TiC are about 2.5 times and 3 times respectively of that without TiC, due to the strengthening effect of both TiC and Cr23C6 carbide reinforcement.
Research progress of external friction coefficient test of powder
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Abstract(124) PDF(9)
Abstract:
The external friction behavior between the interface and the powder is affected by such factors as the properties of the powder, surface roughness of the die, the relative motion speed, temperature and pressure, etc. Unreasonable external friction behavior is easy to cause the wear of powder processing equipment and uneven distribution of product density. In order to explore the external friction behavior of powder, the research progress of powder external friction coefficient was thoroughly investigated, and the testing methods of powder external friction coefficient were summarized. According to different loads, the testing methods of powder external friction coefficient are divided into two categories: small load testing method and heavy load testing method. Among them, the testing methods of small load external friction coefficient include slope method and plate method, and the testing methods of heavy load external friction coefficient include rotation method, shear method and closed mold method. Following the above classification methods, the principle, testing equipment and important conclusions of various testing methods are briefly described. The results show that the test methods under small load are only suitable for measuring the external friction coefficient of low-density powder, and the pressing force in the test is generally less than 100 times of powder weight, while the test methods under heavy load are more commonly used for measuring the external friction coefficient of high-density powder. The pressing force in the test varies from material to material, and the pressing force of polymer materials is usually between 500 and 10,000 times of powder weight, while that of metal materials is between 10,000 and 1 million times of powder weight. Our team used the closed mold method to study the relationship between the external friction coefficient of the powder and the performance of the material under small load, and made some achievements. The closed mold method is a useful attempt to measure the external friction coefficient under small load.
Effect of Ball Milling Process on Microstructure and Mechanical Properties of CNTs/Al Composites
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Abstract(115) PDF(12)
Abstract:
Carbon nanotubes/aluminum (CNTs/Al) composite powders were prepared by both wet ball milling and dry ball milling. CNTs/Al composites were fabricated by using a sparking plasma sintering (SPS) combined with a hot extrusion process, and the relationship between preparation process-microstructure-mechanical properties was explored systematically. The results show that wet ball milling can better disperse CNTs than dry ball milling, and significantly reduce the damage to the structure of CNTs. The ethanol ball milling medium has a cooling effect that is helpful to significantly refines the grain size while reducing the cold welding of the powders, resulting in excellent mechanical properties of the composite. The tensile strength of 2%CNTs/Al composites sintered and hot extruded after 6 h wet ball milling reached 207 MPa.
Viscosity Model of CoCrFeMnNi High Entropy Alloy
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Abstract(98) PDF(19)
Abstract:
The viscosity of high entropy alloy liquid atomization process has important influence on atomization effect, but the study on the viscosity of high entropy alloy liquid is less. In this paper, using the existing ternary alloy viscosity model, a new viscosity model of CoCrFeMnNi high-entropy alloy melt with equal molar ratio was established through model expansion. The influence of temperature on the viscosity of five-element high entropy alloy was studied. The viscosity curve was drawn and modified, and the relationship between temperature and the viscosity of high entropy alloy was calculated. The model study shows that the viscosity decreases from 0.0211 Pa·s to 0.0114 Pa·s when the temperature increases from 1360 K to 2000 K. With the increase of the content of five metals, the viscosity of the high entropy alloy increases. Cr metal has the most significant effect on the viscosity of the alloy, while Fe and Co have the same effect on the viscosity. The results of the prediction model of liquid viscosity of five-element high entropy alloy are consistent with the experimental results of thermal state experiment, which has a guiding significance for the regulation of melt viscosity during the atomization process of high entropy alloy.
Effect of Cr on the properties and microstructure of nickel aluminum metal bond
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Abstract(61) PDF(7)
Abstract:
Vacuum hot pressing sintering was used to add Cr powder to the nickel aluminum metal bond in order to improve the mechanical properties of nickel aluminum metal bond. The effects of Cr powder content and sintering temperature on the mechanical properties and microstructure of the nickel aluminum metal bond were studied. The results show that Cr can solution strengthening and the mechanical properties of nickel aluminum metal bond were improved. As the Cr content increases, the flexural strength of the bond increases first and then decreases with the increase of Cr content, while Rockwell hardness shows an overall increase tendency at 800℃.When Cr content is 12 mol%, the optimal flexural strength and Rockwell hardness are 178 MPa and 104.2 HRB, respectively, which are increased by 36.9% and 6.8%.
Weldability and Microstructure Evolution of Powder Metallurgy High Chromium Cast Iron/Low Carbon Steel Welded by Gas Tungsten Arc Welding
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Abstract(110) PDF(4)
Abstract:

In this paper, powder metallurgy high chromium cast iron (PM HCCI) and low carbon steel (LCS) were welded by multi-pass manual gas tungsten arc welding (GTAW), and the effects of welding current on the microstructure evolution and mechanical properties of the weld joint were systematically investigated.The tensile strength of the solder reaches 538.1MPa at 140A, which is 95.3% and 97.4% of the tensile strength of PM HCCI and LCS, respectively. After that, the fracture mechanism of solder was studied. The microhardness of the weld joint decreased from HCCI side to LCS side in the horizontal direction, whereas in the vertical direction its distribution was of M-shape due to secondary tempering and alloying element diffusion/segregation. A microstructure evolution model of the weld joint was proposed. The fusion zone (FZ) mainly consist of austenite and tempered martensite at the welding current of 140A, and there is a single austenite columnar crystals zone between FZ and LCS, while there is a HCCI columnar crystal zone between FZ and sintered HCCI, in which coarsen carbides with branches are distributed along matrix’ s grain boundary.
Microstructure and mechanical properties of the hybrid material fabricated by selective laser melting of 316L stainless steel on a 45# steel substrate
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Abstract(78) PDF(11)
Abstract:
ASTRACT A 316L stainless steel/45# steel hybride material was fabricated by selective laser melting (SLM) 3D printing of gas atomized 316L stainless steel powder on a 45# steel substrate, and its microstructure and mechanical properties were investigated. The results showed that with the scanning speed (ν) of 1000 mm?s-1, laser power (P) of 225 W, powder bed thickness (d) of 30μm and scanning track spacing (h) of 100 μm, the SLM 316L stainless steel had the least defects, and was almost fully dense. With these process parameters, the SLM 316L stainless steel and 45# steel substrate achieved excellent metallurgical bonding, and the Charpy impact energy of the bonding region was 64 J. When the tensile loading direction was perpendicular to the bonding interface, the fracture occurred within the SLM 316L stainless steel rather than at the bonding interface, and the yield strength (YS), ultimate tensile strength (UTS) and elongation to fracture (EL) were 335.2 MPa, 619.9 MPa and 48.4% respectively, showing that the bonding interface had a higher strength than the SLM 316L stainless steel. The width of the heat affected zone across the bonding interface was about 120 μm, and contained a high number density of martensitic aciculae formed as a result of rapid quenching after solidification, and the microhardness of the bonding zone was obviously higher than that of the SLM 316L stainless steel and the 45# steel substrates. When the tensile loading direction was parallel to the bonding interface, the YS, UTS and EL of the hybrid material were 448.8 MPa, 653.2 MPa and 28.8% respectively.
Synthesis of MoO3 Nanobelts /RGO by One-Step Hydrothermal Process and its Electrochemical Properties
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Abstract(97) PDF(12)
Abstract:
To improve the energy storage performance of MoO3 as a supercapacitor electrode material，MoO3/RGO composites were synthesized by one-step hydrothermal process. The phase structure, morphology and electrochemical properties of the materials were characterized by XRD, SEM, FTIR, cyclic voltammetry, constant current charge discharge, and the effect of hydrothermal process on the microstructure and electrochemical properties of the composites was explored. The results showed that the MoO3 nanoribbons/RGO composites were successfully fabricated by a one-step hydrothermal method. Encouragingly, the specific capacitance of composite material was increased by 17.5% compared with that of pure MoO3 (228 F.g-1). Furthermore, the MoO3 nanoribbons were wrapped by RGO or attached to the surface of RGO in the composite, which induced obvious enhancement of the electrical conductivity as well as the structure stability, and subsequently the ultimate electrochemical properties of the original materials.
Fabrication and properties of the abradable sealing Al2024/hBN composite by hot-pressing sintering
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Abstract(92) PDF(6)
Abstract:
Abradable sealing technique has been extensively used to realize the dynamic seal between rotating and stationary parts of the industrial aircraft engines, and it plays an important role in reducing the heat rate and increasing power output. The Al2024/hBN composite has been produced by hot-pressing sintering process, showing a high density of 2.52 g/cm3 and a Rockwell hardness value up to 90 HR15Y. After ball milling for 120h under an argon atmosphere, the composite’s microstructure significantly changes from spherical particle structure to lamellar structure, and the friction coefficient and volume wear rate reduce to 0.32 and 2.3*10-3 mm3/m*N, respectively. The maximum bending force increases from 1.2 kN to 2.3 kN in the three-point bending test at room temperature.
Research progress and application on TiB2 ceramic
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Abstract(101) PDF(21)
Abstract:
With high melting point, high hardness, high thermal conductivity, excellent electrical conductivity and high temperature oxidation resistance, TiB2 ceramic has been applied in the fields of aerospace, machinery manufacturing, metal smelting, electronic information, and so on. However, the high-end manufacturing application of TiB2 ceramic has been limited by the low density and the difficulty of machine-processing. The densification of TiB2 ceramic could be improved by doping modification, adding sintering additives, optimizing sintering process and so on, which significantly improves mechanical properties. The research progress of high-performance TiB2 ceramic in terms of composition design and sintering processing was reviewed in this paper. The paper also prospected the applications of TiB2 ceramic, such as precision tools, bulletproof armor and cathode tools.
A review of powder reuse in powder bed additive manufacturing
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Abstract(157) PDF(48)
Abstract:
Metal additive manufacturing technology has the characteristics of arbitrary complex structure workpiece forming, and the high cost and inconsistent performance of powder raw materials are the primary barriers to widespread adoption. Without affecting the performance of parts, powder reuse can reduce the cost. Ti-6Al-4V, IN718 alloy and 316L stainless steel and other alloys were studied in this paper, the common preparation methods of different spherical alloy powders were introduced in detail, evolution mechanism of powder physicochemical properties under different powder bed additive manufacturing processes were summarized, the reusability of different alloy powders was discussed and the research trend of powder reuse was proposed. This article provides perspectives and recommendations for relevant researchers, and provide reference for the standardized reuse of alloy powder.
Study on the influence mechanism of force chain on jamming behavior in powder compaction based on 3D discrete element model
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Abstract(180) PDF(46)
Abstract:
To simulate the uniaxial powder compacting process, the 3D particle accumulation is generated using 3D discrete element method technology and the experimental grading ratio. During the powder compacting process, the evolution law and topological properties of the force chains are investigated. The jamming phenomenon is further investigated using the velocity and coordination number of particles, and the correlation mechanism between the force chain and the jamming behavior is discussed. The results show that as the compression strength of the upper die gradually increases from 0 to 60 MPa, the proportion of force chain particles rapidly increases to more than 40%, while the proportion of high stress particles is stable above 12.5%. When the pressure exceeds 60 MPa, the force chains bend and form ring structure, causing the jamming phenomenon. As a result, the jammed point is set to 60 MPa. The jamming phenomenon also effects the powder densification. The axial velocity of the powder particles in the upper area is faster and the rangeability is larger than that of the powder particles in the lower area during the powder compaction process. However, when the compaction process is completed, the densification degree of the powder particles in the upper area is higher than that of the powder particles in the lower area.
Application and Development of Numerical Simulation in Mesoscopic Analysis of Powder Compaction
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Abstract(155) PDF(38)
Abstract:
In recent years, numerical simulation technology has become an important method to study the powder compaction process, and it is used more and more in powder compaction. Many scholars used the discrete element method (DEM) to study the mechanical behavior of powder particles from a mesoscopic perspective, to analyze the characteristics of the force chain and the evolution process of the force chain, and revealed the influence of the mesoscopic structure on the macroscopic properties. The compression deformation mechanisms of different powders were studied by using multi-particle finite element method (MPFEM) at the particle level. In this paper, the application research and development of DEM and MPFEM numerical methods in powder compaction are reviewed, and the difficulties of MPFEM in powder compaction are summarized. The evolution law of the powder force chain and the particle densification mechanism under the changing dynamic load is a direction of future research.
Microstructure and Properties of Alumina Ceramic Particle Reinforced Powder Forged Fe-Ni-Mo-C-Cu Composites
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Abstract(118)
Abstract:
The Fe-Ni-Mo-C-Cu (Q61) composite materials reinforced by different contents of microscaled alumina particles were prepared by powder forging and the microstructures and properties of the composites in the quenched and tempered states were investigated. The Al2O3 particles were distributed homogeneously in the matrix when its amount is 0.15 wt.%. Resultantly, the hardness and yield strength of the tempered composite were increased from HRC 38 and 1106 MPa to HRC 39.8 and 1121 MPa, respectively, while the elongation was decreased from 12% to 6.5%, all in comparison with the single Q61 under the same state. Correspondingly after quenching, the hardness was enhanced from HRC 61.5 to HRC 63.2 and the wear rate was reduced from 5.27×10-6 mm3·m-1·N-1 to 3.08×10-6 mm3·m-1·N-1, lower than that of the typical gear material 40Cr (3.24×10-6 mm3·m-1·N-1). However, the alumina was aggregated gradually to a great extent when the addition content was further improved. Though the yield strength is still improved, the plasticity is reduced significantly for the tempered materials, and the wear rate was greatly increased for the quenched counterparts, showing degraded wear resistance. Overall, the composite with 0.15 wt. % alumina can achieve a better combination of comprehensive mechanical properties and good wear resistance in the tempered and quenched states, respectively. This work can provide useful guidance for the microstructure and property manipulation and the industrial applications for this series of materials prepared by powder forging.
Research progress on high grade aluminum nitride powder and its carbothermal reduction-nitridation preparation
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Abstract(193) PDF(39)
Abstract:
Aluminum nitride (AlN) has the characteristics of high thermal conductivity, good insulation, low thermal expansion coefficient and non-magnetic. Therefore, AlN is considered a key material for high-end semiconductor and electric vacuum devices and has been widely applied in the power device manufacturing in the fields of aerospace, rail transportation, new energy equipment, high power LED, 5G communication, power transmission and industrial control. High-grade powder is the basis of high-performance ceramics. The properties of AlN powder directly affect the forming, sintering, and microstructure and performance of AlN ceramics. Carbothermal reduction method is a promising method to produce AlN powders with high purity, fine particle size and high sinterability. This paper reviews the evaluation metrics of AlN powders and the recent progress of carbothermal reduction method, and proposes the potential directions and trends of future research and industrialization.
Research progress of oxide formation and control in steels by additive manufacturing
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Abstract(138) PDF(35)
Abstract:
High-performance steels have extremely high toughness and fatigue properties, correspondingly the controlling requirements of inclusions on average particle size, particle size distribution and number density are demanding. The oxides in additive manufacturing samples are ineffectively controlled and then affect the mechanical properties, due to the unavoidable increasing of oxygen content in the process of powder preparation. Therefore, the formation, characteristics and influence of oxides in additive manufacturing steels should be clarified, and then control optimizations are performed for compositions and technological process based on the oxygen content in powder, to obtain fine and dispersed oxides and finally realizing the harmless control of oxides. In this paper, the research progress of oxides in additive manufacturing steels is reviewed, including the characteristics and formation of oxides, the influence of oxides on the molten pool, the mechanism of oxide destruction and reconstruction, and the movement of oxides in the molten pool. In addition, the ideas to realize the harmless control of oxides are described, in order to provide references for the future research on the harmless control of oxides in the process of metal additive manufacturing.
Preparation Technology and Properties of Fe2(MoO4)3 Prepared by Recovery Product of Waste MoSi2 Powder
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Abstract(146) PDF(15)
Abstract:
MoO3 was recovered from waste MoSi2 after oxidation reaction by thermal evaporation method, and Fe2(MoO4)3 material was prepared from recovered MoO3 and Fe2O3 by reaction sintering method. The time and temperature of complete oxidation of MoSi2 and the microstructure, linear shrinkage, volume density, spectral properties of prepared Fe2(MoO4)3 material were studied. The results show that, waste MoSi2 powder can be oxidized completely after calcination at 500 ℃ for more than 150 minutes. In the reaction sintering of MoO3 and Fe2O3, with increasing temperature, the reaction sintering is more complete, Fe2(MoO4)3 material has more voids, the linear shrinkage increases and the volume density decreases. Fluorescence spectrum analysis shows that, the photogenerated electron-hole pairs of Fe2(MoO4)3 and MoO3 composite material is more difficult to be recombined than pure Fe2(MoO4)3 which means composite material has higher photocatalytic activity. Using methylene blue as dye, pure Fe2(MoO4)3 has good adsorption performance, while Fe2(MoO4)3 and MoO3 composite show excellent photocatalytic performance, and the mixture of Fe2(MoO4)3 and MoO3 composite has best photocatalytic degradation cycle stability.
Present status and perspective of preparation technology of molybdenum disilicide coating
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Abstract(207) PDF(24)
Abstract:
Molybdenum disilicide (MoSi2) coating has excellent high-temperature oxidation resistance which is widely used for the protection of various materials. Combined with the current research status, the advantages of different processes for preparing MoSi2 coatings and the quality differences of prepared MoSi2 coatings are discussed. In this paper, several preparation method MoSi2 are compared, including plasma spraying method, pack cementation method, slurry method, molten salt method, magnetron sputtering method, chemical vapor deposition method, laser cladding method and spark plasma sintering method. The properties of MoSi2 monolayer and composite coatings prepared by different processes are discussed. Finally, the advantages and disadvantages of MoSi2 coatings prepared by different processes are summarized preparing. The improvement of the MoSi2 coating preparation process and the development direction of MoSi2 coating are prospected.
Fabrication, microstructure and properties of W-Cu gradient composites
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Abstract(139) PDF(11)
Abstract:
Three-layer W-Cu gradient composites were prepared by designing different ratios of W / Cu powder, mixing and spark plasma sintering. The microstructure, interface, physical properties, mechanical properties and thermal shock resistance of W-Cu gradient composites at different sintering temperatures were investigated. The results show that，W-Cu gradient composite sintered at 900 °C has high density (95%) and maintains the original design composition of the single layer. The distribution of W and Cu in each gradient layer is uniform. The interface between W and Cu is well bonded without diffusion. The mechanical properties of the W-Cu gradient composite show gradient distribution, and the microhardness of the W-40Cu layer is up to 136 Hv. During the compression process, the W-40Cu layer of the composite firstly fractures, and the highest compressive yield strength is 378 MPa. The thermal conductivity of the W-Cu gradient composite sintered at 900 ℃ is 202 (W·m-1·k-1). After the thermal shock resistance test，W-Cu gradient composite has good thermal shock resistance performance without no crack at the interface.
Damage and microstructure evolution of yttria particle-reinforced tungsten plates under laser thermal shock
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Abstract(94) PDF(2)
Abstract:
Yttria particle-reinforced tungsten plates with different thickness reduction are prepared by powder metallurgy technology combined with rolling process. The transient laser thermal shock experiments are carried out on the samples’ surface with different recrystallization volume fraction which are obtained at different temperatures annealing process, aimed to investigate the surface damage and microstructure evolution under the synergistic effect of recrystallization caused by long-term steady-state heat load and transient thermal shock. Cracks, melting and other damages occur on the sample surface because of the action of thermal shock loading. Moreover, the recrystallization process will accelerate the widening of cracks and the enlargement of melting area, which greatly reduces the ability of the material to resist transient heat loading. The damage level of the samples with 67% thickness reduction is obviously lower than that with 50% thickness reduction under the same power density, and the former has better thermal shock resistance. Both the molten zone is composed by the columnar grains, the width of the columnar grains is associated with the grain size of the initial matrix below, and the columnar grains formed in rolled samples are finer and numerous, while those of the fully recrystallized samples are coarser.
Friction and wear properties of iron copper based powder metallurgy materials under braking conditions
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Abstract(138) PDF(20)
Abstract:
The friction properties and heat resistances of iron-copper-based powder metallurgy friction materials were tested under two different surface pressures and seven continuous braking conditions by using MM3000 friction and wear testing machine, the wear mechanism of friction materials at two different speeds was studied by SEM and EDS. The results showed that at a line speed of 19.40 m?s-1, the coefficient of dynamic friction of the friction material decreases slightly with the increasing of surface pressure, which is 0.267-0.312 at 0.44 MPa and 0.258-0.308 at 0.80 MPa. The kinetic friction coefficient fluctuates more under the first continuous braking condition（Linear velocity 19.40 m?s-1, surface pressure 0.44 MPa, braking energy per unit area 268 J?cm-2）; under other conditions, the kinetic friction coefficient fluctuates less. With the increasing of braking energy, mean kinetic friction coefficient under seven continuous braking conditions varied from 0.300 to 0.334, and the kinetic friction coefficient was above 0.25 without apparent decline, indicating that the iron-copper based powder metallurgy friction materials have better heat resistance. Under 19.40 m?s-1 working condition, the frictional wear mechanism of iron-copper based friction materials is mainly abrasive wear and oxidation wear; under 30.00 m?s-1 working condition, the frictional wear mechanism of iron-copper based friction materials is mainly fatigue wear and oxidation wear.
The hot deformation behavior and microstructure evolution of Mo-14Re alloyprepared by powder metallurgy
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Abstract(181) PDF(40)
Abstract:
The effects of deformation temperature (1100℃~1400℃) and strain rate (0.1s-1 ~ 0.001s-1) on the flow stress and microstructure evolution of Mo-14Re alloy prepared by powder metallurgy were analyzed by Gleeble 1500 thermal simulation test machine. The constitutive equation of Mo-14Re alloy was established by using Arrhenius model of hyperbolic sine. The results show that the flow stress of the Mo-14Re alloy prepared by powder metallurgy decreases with the increase of deformation temperature or the decrease of strain rate during hot deformation, and the true stress-true strain curve shows obvious work hardening and dynamic softening phenomenon. The dynamic softening behavior is mainly attributed to the dynamic recrystallization of Mo-14Re alloy at low strain rates (0.01s-1 and 0.001s-1) or high deformation temperature (>1200℃) during hot compression. The nucleation mode is grain boundary protruding nucleation. With the decrease of strain rate or the increase of temperature, the recrystallization of Mo-14Re alloy is mainly attributed to the dynamic recrystallization at low strain rates (0.01s-1 and 0.001s-1) or high deformation temperature (> 1200℃). The degree of recrystallization increases and the grains grow up. At 1400℃ and strain rate 0.001s-1, Mo-14Re alloy has been completely recrystallized.
Effects of extrusion ratio and extrusion temperature on the microstructure and mechanical properties of 6063 aluminum alloy prepared by hot extrusion consolidation of chips
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Abstract(193) PDF(17)
Abstract:
6063 aluminum alloy samples were prepared by thermomechanical consolidation of alloy chips which involves hot extrusion of chip compacts with extrusion ratios of 9:1 and 25:1 and extrusion temperatures of 450 ℃ and 500 ℃, respectively, followed by a T6 heat treatment. The microstructure , tensile properties and fracture behavior of the samples were studied. The results show that with an extrusion temperature of 500 ℃, dynamic recrystallization occurs in the consolidated samples, and the recrystallized grains are confined within the chips and become elongated. With the increase of extrusion ratio, the grains become finer, the yield strength (YS) and ultimate tensile strength (UTS) increase from 198 and 242 MPa to 252 and 275 MPa, respectively, and the elongation to fracture decreases clearly from 19.5%-15.2%. With an extrusion ratio of 25:1, an decrease of the extrusion (EL) from 500 ℃ to 450 ℃ caused a slight increase of the average grain size, the YS and UTS remain almost unchanged, and the elongation to fracture decreases clearly from 15.2% to 12.1%. For comparison, 6063 aluminum alloy samples were also prepared by hot extrusion of ingots under the same conditions followed by the same T6 heat treatment. It was found that the average grain size changes little with the increase of extrusion ratio, but decreases slightly with the decrease of extrusion temperature. The tensile properties remain almost unchanged in these two cases (YS: 192-202 MPa, UTS: 228-237 MPa, EL: 18.4-19.1%). Both types of materials exhibit ductile tensile fracture, but the mode of fracture is different, with the material prepared by consolidation of chips shows interchip decohesion. Correlations among processing conditions, microstructure and mechanical properties are discussed.
Effects of the types of raw iron powders on the microstructure and properties of Fe-29Ni-17Co Kovar alloys
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Abstract(140) PDF(24)
Abstract:
Fe-29Ni-17Co (Kovar alloy) powder mixes were obtained by mixing nickels and cobalt powders with reduced and carbonyl iron powder respectively, and sintered Fe-29Ni-17Co samples were prepared by pressing the powder mixes and sintering at different temperatures. Microstructure and properties of the sintered Fe-29Ni-17Co samples were investigated in accordance with the types of the iron powders and sintering temperature. The results show that sintered Fe-29Ni-17Co samples prepared from the carbonyl iron powder have higher relative density and better comprehensive performance. After sintered at 1250 ℃ for 2 h in H2 atmosphere, relative density of 97.51 % (8.11 g·cm-3) was obtained for samples prepared from the carbonyl iron powders, which is 1.4 % higher than that from reduced iron powders. Hardness and tensile strength of the samples prepared from carbonyl iron powders reach 84.6HRB and 533.8 MPa, respectively, and thermal conductivity, average thermal expansion coefficient (20~400 ℃) and electrical resistivity are 16.45 W·m-1·K-1, 4.71×10-6 K-1 and 0.38 Ω·cm, respectively. More uniform austenite distribution was observed in the sintered samples prepared from carbonyl iron powders, and there have less martensite transformation after low temperature treatment.
Research on flow field characteristic of close-coupled gas atomizing nozzle
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Abstract(617) PDF(10)
Abstract:
The atomization nozzle is the core component of the close-coupled gas atomization method to prepare metal powder. The pressure at the tip of the melt delivery tube and the pressure at the stagnation point are very important for the smooth outflow of the molten metal during the atomization process. When the tip of the melt delivery tube is under positive pressure, the molten metal cannot flow out of the nozzle smoothly, and in severe cases, it will cause the back spray of the molten metal. The greater the pressure at the stagnation point, the greater the impact force of the atomized gas acting on the molten metal flowing out of the melt delivery tube, and the better the crushing effect. In this paper, the effects of atomization pressure, protrusion length and cone-apex angle on the pressure at the tip of the melt delivery tube and the pressure at the stagnation point are studied experimentally and numerically. The results show that with the increase of atomization pressure, the length of the negative pressure zone remains basically unchanged, while the pressure at the stagnation point increases; Increased protrusion length expands the negative pressure zone and reduces the pressure at the stagnation point; As the cone-apex angle of the melt delivery tube increases, the pressure at the tip of the tube will transition from negative pressure to positive pressure, resulting in the failure of atomization.
Analysis of microstructure and mechanical properties of solid-state recycled H11 steel after annealing
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Abstract(150) PDF(0)
Abstract:
In the previous study on the H11 steel fabricated by thermomechanical consolidation of powders made from grinding turning chips, it was found that the toughness of the experimental steel prepared with the powders of different particle sizes was poor. This paper studies the effect of annealing heat treatment on microstructure and mechanical properties of the consolidated steel. The heat treatment involves heating from room temperature to 880 °C at a rate of 10 °C/min, holding for 3 h, cooling in the furnace to 750 °C, holding for 4 h, cooling in the furnace to 550 °C and then air cooling. The mechanical property test, and XRD and SEM observations show the following findings. After the isothermal spheroidizing annealing treatment, the microstructure consists of spherical pearlite and dispersed granular carbide particles. The ductility of the material becomes better with the elongation to fracture increasing from 3.4 % to 12.8 % after the heat treatment, but the tensile strength and hardness decrease. The powder particle size affect the strength and toughness of consolidated H11 steel. The smaller the particle size, the more severe the oxidation after high temperature extrusion forging, and the worse the strength and toughness.
Effect of laser power on Microstructure and properties of laser selective melting maraging steel
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Abstract(202) PDF(3)
Abstract:
18-Ni300 martensitic steel was prepared by laser selective melting. The effect of laser power on the microstructure and properties of 18ni-300 martensitic steel was studied. The results show that with the increase of laser power, the grain size of cladding layer becomes smaller and the microstructure is dense; The side hardness of the sample is higher than that of the upper surface, and the tensile strength and elongation increase first and then decrease. When the laser power is 300W and the scanning speed is 1000mm / s, the comprehensive mechanical properties of the sample are the best: the tensile strength is 1217MPa, Vickers hardness is 377HV , and elongation at break is 8.93%. Its EBSD shows that in XOZ plane and YOZ plane, columnar crystals grow along the growth direction (z direction), the grains show weak texture, and there are many small angle grain boundaries, and the grain size is less than 10 μ m. It reflects the excellent mechanical properties of martensitic stainless steel to a certain extent. This study can provide reference for the reasonable selection of selected laser melting process parameters of martensitic aging steel.
Study on the Centrifugal Spray Granulator Process for Tungsten Heavy Alloy Powder
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Abstract(381) PDF(7)
Abstract:
For the development of ready to press powder of tungsten heavy alloy, the influences of process parameters of centrifugal spray granulation were investigated. The results showed that the bulk density, flow rate, particle size distribution and morphology of granulated powder were significantly influenced by the solid loading and dynamic viscosity of slurry, inlet and outlet temperature, feed rate and rotational speed of atomizer disk. A set of process parameters were obtained included the solid loading of 70%(volume percentage is 9.7%) and dynamic viscosity of 2.5 Pa?s for the slurry, the inlet and outlet temperatures of 300 ℃ and 120 ℃ respectively, the feeding rate 90 mL?min-1 of peristaltic pump , and the rotational speed 9800 r?min-1 of atomizer disk. The proper granulated powder with good flowability and narrow particle size distribution can be obtained by using these parameters, the D50 and D90 of granulation powder are 52 μm and 91 μm respectively, and the flow rate is 14.4 s?(50g)-1.

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