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Thermal coupling analysis and residual stress prediction of aluminum alloy SLM
LIU Shangyang, YANG Bo, MAO Jian
, Available online  
Abstract(39) HTML (21) PDF(3)
Abstract:
In this paper, the thermal and mechanical coupling analysis of AlSi10Mg SLM forming process is carried out by using ANSYS finite element analysis software and experimental verification is carried out. Aiming at the problem that SLM numerical simulation of aluminum alloy is not accurate enough and the residual stress prediction efficiency is low, JMatPro software is used to calculate the nonlinear thermal physical property parameters of AlSi10Mg at different temperatures, and the material state transformation is realized by UDMAT subroutine of ANSYS, so as to improve the accuracy of numerical simulation. The influence of different laser process parameters on temperature field and stress field was studied through the thermodynamic coupling numerical model established. Finally, the corresponding AlSi10Mg sample printing experiment was carried out, and the residual stress of the sample was measured by X-ray stress analyzer. The results show that there are obvious peaks in the curves during the scanning of each layer, and good remelting lap between tracks and layers can be achieved. With the decrease of scanning rate or the increase of laser power, the maximum temperature and molten pool size increase. In the forming process, the stress along the scanning direction is the largest, and the stress perpendicular to the scanning direction is the smallest. The error between the residual stress and the experimental value obtained by the thermodynamic coupling model is less than 8%. The residual stress of SLM can be predicted by the thermodynamic coupling model.
Effect of nano-diamond on mechanical properties of polycrystalline cubic boron nitride
ZHANG Qunfei, XIAO Changjiang, MA Jinming, TANG Lihui, LI Zhengxin
, Available online  
Abstract(73) HTML (18) PDF(17)
Abstract:
Polycrystalline cubic boron nitride (PcBN) was sintered at the high temperature of 1500 ℃ under the pressure of 5.5 GPa, using cubic boron nitride (cBN) powders as the raw materials, Al powders and Si powders as the binders, and nano-diamond as the additive. The effects of nano-diamond mass fraction on the phase composition, microstructure, density, hardness, fracture toughness, and wear ratio of PcBN were investigated. The results show that, the addition of nano-diamond has the great influence on the performance of PcBN. When the diamond mass fraction is 5%, the relative density of PcBN reaches the maximum as 98.5%. Vickers hardness, fracture toughness, and wear ratio of the PcBN samples increase and then drop as the nano-diamond content increases. When the nano-diamond mass fraction is 5%, the hardness, fracture toughness, and wear ratio of PcBN reach the highest values, which are 47 GPa, 4.89 MPa·m1/2, and 6350, respectively.
Powder metallurgy in China: markets, applications and the impact of vehicle electrification
CAO Yang, QIU Yaohong
, Available online  
Abstract(135) HTML (71) PDF(29)
Abstract:
Over the past three decades, China has grown into a powerhouse for powder metallurgy (PM) parts production. Supported by a thriving and diversified domestic market for PM parts, the domestically-owned PM companies are now competing with the international market leaders. China’s PM industry, however, faces the same challenges as the rest of the world’s producers — the transition to vehicle electrification. China is a huge market and PM applications in China are diverse. The rapid development of new energy vehicles is a challenge, but it will also bring new development opportunities. Under the background of automobile industry transformation, the development and current situation of China’s PM parts industry were analyzed in this paper, the development trend of China's automobile industry and the impact on the PM industry were summarized, the coping strategies with the transformation of the automobile industry were proposed, and the future development prospects of the PM industry were prospected.
Effect of rotary swaging deformation on microstructure and mechanical properties of tungsten alloys
SHAN Dongdong, WANG Ling, QIN Yingnan, GUAN Ke
, Available online  
Abstract(53) HTML (16) PDF(11)
Abstract:
The 93WNiFe alloys were deformed by rotary swaging process to obtain the high-performance tungsten alloys. The effect of rotary swaging deformation on the mechanical properties and microstructure of the 93WNiFe tungsten alloys were studied. The results show that, with the increase of deformation, the W grains in 93WNiFe tungsten alloys are elongated from spheroid to long strip, the tensile strength at room temperature increases from 982 MPa to 1622 MPa, and the elongation decreases from 35.5% to 5.5%. When the deformation of rotary swaging is less than 15%, the Rockwell hardness of the 93WNiFe alloys increases rapidly and the impact toughness decreases rapidly at room temperature with the increase of deformation. When the deformation is greater than 15%, the Rockwell hardness increases slowly, and the impact toughness decreases slowly at room temperature. When the deformation is 30%, the maximum Rockwell hardness is HRC 47.2, and the minimum impact toughness at room temperature is 30.80 J·cm−2. There are a small number of W grain cleavage fractures, a large number of W–bond phase interface fractures, W–W interface fractures, and binder phase dimple fractures in the sintered 93WNiFe alloys without deformation. With the increase of deformation, the number of W grain cleavage fractures increases gradually, and the number of W–bond phase interface fractures, W–W interface fractures, and binder phase dimple fractures decrease gradually.
Optimization on hydrogenation-dehydrogenation preparation of titanium powders by SHS
ZHOU Kexin, YANG Zhanxin, WANG Junbo, MU Minxuan, CHEN Jian, QI Guochao
, Available online  
Abstract(106) HTML (31) PDF(11)
Abstract:
To optimize the hydrogenation-dehydrogenation process for preparing titanium powders by self-propagating high-temperature synthesis (SHS) method, the traditional steel ball milling process was replaced by the new closed-loop air current grinding process, and the traditional evacuation process for dehydrogenation process was replaced by the decompression-ignition process. The microstructure, phase component, chemical composition, and particle size distribution of the samples prepared by the optimization process were studied. In the results, the hydrogen mass fraction in the titanium hydride samples is high (4.662%) after SHS hydrogenation, and the particle size distribution of the TiH2 particles is uniform with the range of 40~250 μm after the closed-loop air flow grinding process. The new dehydrogenation process is beneficial to control the N, O, and C content in the titanium powder samples.
Effects of induced Cu content on the microstructure and thermal properties of Mo–Cu composites
WU Mingjie, ZHANG Xinzhe, ZHAO Jianguo, ZHAO Yuanchao, ZHANG Huailong, GUO Yajie
, Available online  
Abstract(74) HTML (28) PDF(5)
Abstract:
Mo–Cu composites were fabricated by induced infiltration method. Mo–Cu composites with different Cu contents were prepared by adjusting the induced Cu mass fraction (0～30%). The effects of induced Cu content on the microstructure and properties of the composites were studied. The results show that the content of the induced Cu significantly influences the microstructure of the Mo–Cu composites. When the mass fraction of the induced Cu gradually increases from 0% to 20%, the porosity of the composite is greatly reduced, the distribution of Mo and Cu phases is more uniform, and the single-phase segregation in the microstructure is reduced. However, when the mass fraction of the induced Cu increases to 30%, the microstructure uniformity of the composites becomes worse and the number of pores increases significantly. The electrical conductivity and thermal conductivity of the Mo–Cu composites increase with the increase of the final Cu content in the composites. When the final Cu mass fraction is 40.46%, the relative density of the composite reaches to the peak of 98.1%. Correspondingly, the electrical conductivity and thermal conductivity of the composite are also the highest values, which are 52.69 %IACS and 203.94 W·m−1·K−1, respectively. Unexpectedly, the thermal expansion coefficient of the composites also increases with the increase of the final Cu content. The combination of regulating the induced Cu and exploring suitable infiltration processes is expected to obtain the Mo–Cu composites with improved comprehensive properties.
Effect of nano-ZrC powders on microstructure and properties of 90W−7Ni−3Fe alloys
SU Xuwen, HE Zhi, YAN Shuxin, DONG Longlong, SUN Guodong
, Available online  
Abstract(68) HTML (33) PDF(16)
Abstract:
To effectively inhibit the growth of tungsten grains during the liquid phase sintering, the ZrC dispersion-strengthened heavy tungsten alloys (WHAs) were prepared by liquid phase sintering at 1500 ℃. The effects of ZrC mass fraction (1% and 2%) on the microstructure and properties of WHAs were analyzed. The results show that, with the increase of ZrC mass fraction, the relative density and W−W contiguity of WHAs decrease, and the tungsten grains are refined to a certain extent. When the ZrC mass fraction is 1%, the strength-ductility matching effect of WHAs is the best, the relative density reaches 98.4%, the tungsten grain size is 22.17 μm, and the yield strength and compressive strength (40% deformation) reach 791 MPa and 2179 MPa, respectively, which are increased by 8.35% and 38.70%, compared with WHAs without ZrC (730 MPa and 1570 MPa).
First-principles calculation and experimental study on the influence mechanism of diffusion activation energy of Cu atoms in current-assisted sintering
ZHAO Bo, ZHANG Xiaomin, ZHAO Zhipeng, WU Qiong, GAO Xin
, Available online  
Abstract(113) HTML (139) PDF(23)
Abstract:
The mechanism of rapid densification is one of the bases of the electro-induced effect in current-assisted sintering. This mechanism has been characterized as the effect of electric field intensity on the apparent (or diffusion) activation energy of sintering, and significant progress has been made. In this paper, the effects of applied electric field on the diffusion activation energy of crystal Cu are studied from two aspects of first-principles calculation and current-assisted sintering experiment. The results of the two studies reveal that the diffusion activation energy shows an obvious trend of regular decreasing trend under the action of electric field or current. In addition, to verify the positive correlation of the decreasing rule of two methods, current-assisted sintering experiment was conducted in which the inner diameter of the graphite die was varied to adjust the current density.
Thermal deformation behavior and microstructure evolution of Mo–14Re alloys prepared by powder metallurgy
XUE Jianrong, LIN Xiaohui, LI Yanchao, LIANG Jing, ZHANG Xin, GAO Xuanqiao, YANG Yichao, ZHANG Wen
, Available online  
Abstract(188) HTML (37) PDF(40)
Abstract:
The constant strain rate compression experiment of powder metallurgy Mo–14Re alloys was carried out by Gleeble 1500 thermal simulation tester. The effects of deformation temperature (1100~1400 ℃) and strain rate (0.100~0.001 s−1) on the flow stress and microstructure evolution were analyzed. The constitutive equation of Mo–14Re alloys was established by hyperbolic sinusoidal Arrhenius model. The results show that, the flow stress of powder metallurgy Mo–14Re alloys decreases with the increase of deformation temperature or the decrease of strain rate during the thermal deformation, and the true stress-true strain curve shows the obvious work hardening and dynamic softening phenomenon. The dynamic softening behavior is mainly attributed to the dynamic recrystallization of Mo–14Re alloys at low strain rate (0.010 s−1 and 0.001 s−1) or high deformation temperature (>1200 ℃) during the thermal compression. The nucleation mode is grain boundary protruding nucleation. With the decrease of strain rate or the increase of temperature, the degree of recrystallization continues to increase, the grains continue to grow, and the Mo–14Re alloys are completely recrystallized at 1400 ℃ with the strain rate of 0.001 s−1.
Effects of raw iron powder type on the microstructure and properties of Fe–29Ni–17Co Kovar alloys
ZHANG Mei, CHEN Wenchao, CHEN Pengqi, CHENG Jigui
, Available online  
Abstract(140) HTML (30) PDF(24)
Abstract:
Fe–29Ni–17Co powder mixes were obtained by mixing nickels and cobalt powders, using the reduced iron powders and carbonyl iron powders as the raw materials, respectively, and the sintered Fe–29Ni–17Co Kovar alloy samples were prepared by pressing and sintering at the different temperatures. The effects of the raw iron powder type and sintering temperature on the microstructure and properties of the sintered body were investigated. The results show that the sintered samples prepared by the carbonyl iron powders have the higher relative density and the better comprehensive performance, the relative density of the sintered body sintered at 1250 ℃ is 97.51%, which is about 1.40% higher than that of the sintered body prepared by the reduced iron powders. The hardness and tensile strength of the samples prepared by the carbonyl iron powders reach HRB 84.6 and 533.8 MPa, respectively, and the 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. The distribution of austenite in the sintered body obtained from the carbonyl iron powders is more uniform, the microstructure stability is better after the low temperature treatment, and the degree of martensitic transformation is lower.
Microstructure and phase stability analysis of laser cladding CoCrCu0.4FeNi high entropy alloy coatings
XU Hongyang, LU Jinbin, PENG Xuan, MA Mingxing, MENG Wenglu, LI Hongzhe
, Available online  
Abstract(224) HTML (98) PDF(8)
Abstract:
To improve the hardness and wear resistance of parts, the Co, Cr, Cu, and Ni elemental metal powders were used to prepare the CoCrCu0.4FeNi high entropy alloy coatings on Q235 steel substrate by laser cladding. The microstructure of the high entropy alloy coatings was analyzed by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), and the microhardness of the coatings was measured. The lattice and elastic constants of each phase in the coatings were calculated by the first principle. The results show that, the coatings show the good metallurgical bond with the substrate without the macro-cracks and pores. The microstructure of the coatings is mainly composed of dendrite and interdendrite. The dendrite is one kind of face-centered cubic phase (FCC1), rich Cu and poor Cr, the interdendrite is another kind of face-centered cubic phase (FCC2), rich Cr and poor Cu. The thickness of the coatings is about 1.50~1.98 mm, and the size of the coating dendrite is about 7.9~10.4 μm. The microhardness of the coatings is about HV0.2 170~230, about 1.7 times that of the substrate, and the hardness of the coatings gradually decreases with the increase of the distance from the coating surface. In addition, the lower the laser power, the higher the scanning speed, the finer the dendrite, the stronger the effect of fine grain strengthening, and the higher the hardness of the coating. The error between the calculated lattice constant and the experimental value of face-centered cubic (FCC) phases in the coatings is 1.33%~2.60%. The formation heat of FCC phases is negative, and the elastic constants C11, C12, and C44 meet the mechanical stability constraints of the cubic high entropy alloy, showing the FCC phases are stable. The FCC phases at the dendrite and interdendrite are generally present as the characteristics of toughness according to the ratio of shear modulus to bulk modulus (G/B)＜0.57 and Poisson's ratio (ν)＞0.26. From the lower part to the upper part of the coatings, the calculated elastic modulus and hardness increase gradually, which is consistent with the variation law of the experimental data.
Research on flow field characteristic of close-coupled gas atomizing nozzles
BAN Wei, CHEN Jiaqi, LIU Lulu, GE Tao, ZHANG Shuai
, Available online  
Abstract(628) HTML (63) PDF(11)
Abstract:
The atomization nozzle is the core component for the metal powder preparation by close-coupled gas atomization method. The pressure at the tip of the melt delivery tube and the stagnation point is very important for the smooth outflow of the molten metal during the atomization process. When the tip of the melt delivery tube is positive pressure, the molten metal cannot flow out of the nozzle smoothly, and in severe cases, it may 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. The effects of atomization pressure, protrusion length, and cone-apex angle on the pressure at the tip of the melt delivery tube and the stagnation point were studied by mathematical modeling, experimental verification, and numerical simulation in this paper. The results show that, with the increase of atomization pressure, the length of the negative pressure area remains basically unchanged, while the pressure at the stagnation point increases. With the increase of the melt delivery tube elongation, the length of the negative pressure area increases and the pressure at the stagnation point decreases. With the increase of the cone-apex angle of the melt delivery tube, the pressure at the tip of tube changes from the negative to the positive, resulting in the failure of atomization.

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