A Laval-type supersonic gas atomizer was designed for low-pressure gas atomization of molten metals. The principal design ob-jectives were to produce small-particle uniform powders at lower operating pressures by impr...A Laval-type supersonic gas atomizer was designed for low-pressure gas atomization of molten metals. The principal design ob-jectives were to produce small-particle uniform powders at lower operating pressures by improving the gas inlet and outlet structures and op-timizing structural parameters. A computational fluid flow model was developed to study the flow field characteristics of the designed atom-izer. Simulation results show that the maximum gas velocity in the atomization zone can reach 440 m·s-1;this value is independent of the atomization gas pressure P0 when P0〉0.7 MPa. When P0=1.1 MPa, the aspiration pressure at the tip of the delivery tube reaches a mini-mum, indicating that the atomizer can attain the best atomization efficiency at a relatively low atomization pressure. In addition, atomization experiments with pure tin at P0=1.0 MPa and with 7055Al alloy at P0=0.8 and 0.4 MPa were conducted to evaluate the atomization capa-bility of the designed atomizer. Nearly spherical powders were obtained with the mass median diameters of 28.6, 43.4, and 63.5μm, respec-tively. Compared with commonly used atomizers, the designed Laval-type atomizer has a better low-pressure gas atomization capability.展开更多
The paper aims at modeling and simulating the atomization process of the close-coupled ring-hole nozzle in vacuum induction gas atomization(VIGA)for metallic powder production.First of all,the primary atomization of t...The paper aims at modeling and simulating the atomization process of the close-coupled ring-hole nozzle in vacuum induction gas atomization(VIGA)for metallic powder production.First of all,the primary atomization of the ring-hole nozzle is simulated by the volume of fluid(VOF)coupled large eddy simulation(LES)model.To simulate the secondary atomization process,we use the method of selecting the droplet sub-model and the VOF model.The results show that the ring-hole nozzle forms a gas recirculation zone at the bottom of the delivery tube,which is the main reason for the formation of an annular liquid film during the primary atomization.In addition,the primary atomization process of the ring-hole nozzle consists of three stages:the formation of the serrated liquid film tip,the appearance and shedding of the ligaments,and the fragmentation of ligaments.At the same time,the primary atomization mainly forms spherical droplets and long droplets,but only the long droplets can be reserved and proceed to the secondary atomization.Moreover,increasing the number of ring holes from 18 to 30,the mass median diameter(MMD,d_(50))of the primary atomized droplets decreases first and then increases,which is mainly due to the change of the thickness of the melt film.Moreover,the secondary atomization of the ring-hole nozzles is mainly in bag breakup mode and multimode breakup model,and bag breakup will result in the formation of hollow powder,which can be avoided by increasing the gas velocity.展开更多
A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the all...A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the alloy was very fine and its microstructure was mainly consisted of Si crystals plus intermetallic compound A19FeSi3, which were.very fine and uniformly distributed.展开更多
17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, sc...17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy (SEM), and the X-ray diffraction (XRD) technique. The results show that the mass median particle diameter is about 19.15 prn. Three main types of surface microstructures are observed in the powders: well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.展开更多
The crucible-free electrode induction melting gas atomization(EIGA) technology is an advanced technology for preparing ultra-clean nickel-based superalloy powders. One of the key issues for fabricating powders with ...The crucible-free electrode induction melting gas atomization(EIGA) technology is an advanced technology for preparing ultra-clean nickel-based superalloy powders. One of the key issues for fabricating powders with high quality and yield is the consecutive induction melting of a superalloy electrode. The coupling of a superalloy electrode and coil,frequency, output power, and heat conduction are investigated to improve the controllable electrode induction melting process. Numerical simulation results show that when the coil frequency is 400 kHz, the output power is 100 kW, superalloy liquid flow with a diameter of about 5 mm is not consecutive. When the coil frequency is reduced to 40 kHz, the output power is 120 kW, superalloy liquid flow is consecutive, and its diameter is about 7 mm.展开更多
2wt%TiB_(2)/Cu composite powders were fabricated in situ by reactive gas atomization.The fabricated composite powder exhibits high sphericity,and the powder sizes range from 5μm to 150μm.The morphology of the Cu mat...2wt%TiB_(2)/Cu composite powders were fabricated in situ by reactive gas atomization.The fabricated composite powder exhibits high sphericity,and the powder sizes range from 5μm to 150μm.The morphology of the Cu matrix and the distribution of the TiB2 particles in the composite powders vary with the powder size.The critical transitions of interface morphologies from dendritic-to-cellular and cellular-to-planar interfaces occurs when the composite powder sizes decrease to 34μm and 14μm,respectively.Compared with pure Cu droplets,the composite droplets undergo critical transition of the interface morphologies at a smaller droplet size corresponding to a higher cooling rate because the existence of TiB2 particles can cause instability in the advancing solidification front and heterogeneous nucleation.With decreasing powder size,the extent of the TiB_(2) particle interdendritic segregation decreases as the result of enhanced engulfment of TiB2 particles by the advancing solidification front.展开更多
Super-clean and super-spherical FGH4095 superalloy powder is produced by the ceramic-free electrode inductionmelt inert gas atomization(EIGA) technique.A continuous and steady-state liquid metal flow is achieved at ...Super-clean and super-spherical FGH4095 superalloy powder is produced by the ceramic-free electrode inductionmelt inert gas atomization(EIGA) technique.A continuous and steady-state liquid metal flow is achieved at high-frequency(350 k Hz) alternating current and high electric power(100 k W).The superalloy is immersed in a high-frequency induction coil,and the liquid metal falling into a supersonic nozzle is atomized by an Ar gas of high kinetic gas energy.Numerical calculations are performed to optimize the structure parameters for the nozzle tip.The undesired oxidation reaction of alloying elements starts at 1000℃ with the reaction originating from the active sites on the powder surfaces,leading to the formation of oxides,MexOy.The role of active sites and kinetic factors associated with the diffusion of oxygen present in the atomization gas streams are also examined.The observed results reveal that the oxidation process occurring at the surface of the produced powders gradually moves toward the core,and that there exists a clear interface between the product layer and the reactant.The present study lays a theoretical foundation for controlling the oxidation of nickel-based superalloy powders from the powder process step.展开更多
The resonant behaviors of an ultra-sonic gas atomization nozzle with a zero mass-flux jet actuator were numerically investigated with FLUENT software by using a double precision unsteady two-dimensional pressure-based...The resonant behaviors of an ultra-sonic gas atomization nozzle with a zero mass-flux jet actuator were numerically investigated with FLUENT software by using a double precision unsteady two-dimensional pressure-based solver. The Spalart-Allmaras turbulence model was adopted in the simulations. Numerical results indicated that the oscillation properties of the gas efflux were effectively improved. Several resonatory frequencies corresponding to different vibration modes of gas were distinguished in the nozzle. With the changing of nozzle geometric parameters, different characters among those modes were elucidated by analyzing the propagations of pressure waves.展开更多
Al-20Sn-1Cu powders were prepared by gas atomization in an argon atmosphere with atomizing pressures of 1.1 and 1.6 MPa. The characteristics of the powders are determined by means of dry sieving, scanning electron mic...Al-20Sn-1Cu powders were prepared by gas atomization in an argon atmosphere with atomizing pressures of 1.1 and 1.6 MPa. The characteristics of the powders are determined by means of dry sieving, scanning electron microscopy (SEM), optical microscopy (OM), and X-ray diffractometry (XRD). The results show that the powders exhibit a bimodal size distribution and a higher gas pressure results in a broad size distribution. All particles in both cases are spherical or nearly spherical and satellites form on the surface of coarse particles. Dendritic and cellular structures coexist in the particle. With decreasing particle diameter, the secondary dendrite arm spacing (SDAS) decreases and the cooling rate increases. The particles processed under high gas atomization pressure (1.6 MPa) exhibit a lower SDAS value and a higher cooling rate than those of the same size under low gas atomization pressure (1.1 MPa). The XRD results show that the Sn content increases with decreasing particle size.展开更多
In this study, the microstructure evolution of rapidly solidified ASP30 high-speed steel particles was predicted using a simulation method based on the cellular automaton-finite element (CAFE) model. The dendritic g...In this study, the microstructure evolution of rapidly solidified ASP30 high-speed steel particles was predicted using a simulation method based on the cellular automaton-finite element (CAFE) model. The dendritic growth kinetics, in view of the characteristics of ASP30 steel, were calculated and combined with macro heat transfer calculations by user-defined functions (UDFs) to simulate the microstructure of gas-atomized particles. The relationship among particle diameter, undercooling, and the convection heat transfer coefficient was also inves- tigated to provide cooling conditions for simulations. The simulated results indicated that a columnar grain microstructure was observed in small particles, whereas an equiaxed microstructure was observed in large particles. In addition, the morphologies and microstructures of gas-atomized ASP30 steel particles were also investigated experimentally using scanning electron microscopy (SEM). The experimental re- suits showed that four major types ofmicrostructures were formed: dendritic, equiaxed, mixed, and multi-droplet microstructures. The simu- lated results and the available experimental data are in good agreement.展开更多
Gas atomization is now an important production technique for Fe-based amorphous alloy powders used in additive manufacturing,particularly selective laser melting,fabricating large-sized Fe-based bulk metallic glasses....Gas atomization is now an important production technique for Fe-based amorphous alloy powders used in additive manufacturing,particularly selective laser melting,fabricating large-sized Fe-based bulk metallic glasses.Using the realizable k-εmodel and discrete phase model theory,the flow dynamics of the gas phase and gas-melt two-phase flow felds in the close-wake condition were investigated to establish the correlation between high gas pressure and powder particle characteristics.The locations of the recirculation zones and the shapes of Mach disks were analyzed in detail for the type of discrete-jet closed-coupled gas atomization nozzle.In the gas-phase flow feld,the vortexes,closed to the Mach disk,are found to be a new deceleration method.In the two-phase flow feld,the shape of Mach disk changes from“S”-shape to“Z”-shape under the impact of the droplet flow.As predicted by the wave model,with the elevation of gas pressure,the size of the particle is found to gradually decrease and its distribution becomes more concentrated.Simulation results were compliant with the Fe-based amorphous alloy powder preparation tests.This study deepens the understanding of the gas pressure impacting particle features via gas atomization,and contributes to technological applications.展开更多
The instability theory of fluid flow is applied in gas atomization and the results show that the instability of interfacial wave is the main cause of gas atomization. The size of the droplets and its change with param...The instability theory of fluid flow is applied in gas atomization and the results show that the instability of interfacial wave is the main cause of gas atomization. The size of the droplets and its change with parameters are also studied, the results are compatible with the experiments.展开更多
Processing soft ferromagnetic glass-forming alloys through gas atomization and consolidation is the most effective technique to produce bulk samples.The commercial viability of these materials depends on commercial pu...Processing soft ferromagnetic glass-forming alloys through gas atomization and consolidation is the most effective technique to produce bulk samples.The commercial viability of these materials depends on commercial purity feedstock.However,crystallization in commercial purity feedstock is several orders of magnitude faster than in high purity materials.The production of amorphous powders with commercial purity requires high cooling rates,which can only be achieved by extending the common process window in conventional gas atomization.The development of novel cooling strategies during molten metal gas atomization on two model alloys({(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 and Fe76B10Si9P5)is reported.Hydrogen inducement during liquid quenching significantly improved the glass-forming ability and soft magnetic properties of{(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 powders.Spark plasma sintering experiments verified that amorphous rings could be produced regardless of the cooling strategies used.While the saturation magnetization was almost unaffected by consolidation,the coercivity increased slightly and permeability decreased significantly.The magnetic properties of the final bulk samples were independent of feedstock quality.The developed cooling strategies provide a great opportunity for the commercialization of soft ferromagnetic glass-forming alloys with commercial purity.展开更多
The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperat...The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperature range of 1323-1473 Kand strain rate range of 0.001-0.5s^(-1).The calculated activation energy in the above variational ranges of temperature and strain rate possesses a low activation energy value of approximately 365.6kJ/mol based on the constitutive relationship models developed with the Arrhenius-type constitutive model respectively considering the strain rate and deformation temperature.The hot working flow behavior during the deformation process was analyzed combined with the microstructural evolution.Meanwhile,the processing maps during the deformation process were established based on the dynamic material model and Prasad instability criterion under different deformation conditions.Finally,the optimal hot processing window of this alloy corresponding to the wide temperature range of 1353-1453 Kand the low strain rate of 0.001-0.1s^(-1) was obtained.展开更多
Microstructure, thermodynamics and electrochemicalproperties of novel RE (NiAlCu)x(x= 4.5, 4.9, 5.6 ) microcrystalline hydrogen-storage alloy powder prepared by gas atomization wasinvestigated. It indicates that alloy...Microstructure, thermodynamics and electrochemicalproperties of novel RE (NiAlCu)x(x= 4.5, 4.9, 5.6 ) microcrystalline hydrogen-storage alloy powder prepared by gas atomization wasinvestigated. It indicates that alloyparticles show relatively regularspherical. Microstructure is composed of the AB5 matrix phase andeutectic double-phase structure withthe AB5 phase and Ni3Al along grainboundaries when x = 5. 6, there is acoexistent structure consisting ofAB5 phase and eutectic doublephase with AB3 and AB phases along grain boundaries at x= 4.5.When x is increased to 4.9, themixed structures are composed ofAB5 and a few AB phases in discontinuous network distribution. Theelectrochemical capacity of alloy is210~300 mAh·g-1, and the activated periods are only 1~3 times.lt seems to be ascribed to the appearance of a great number of freshsurfaces within powder particles resulting from the as-quenched microcrack along the interphase boundaries within particles propagatinggradually in the process of hydrogen-absorption-and dissociation dueto the intrinsic double-phase structure.展开更多
Gas atomization has been studied by using energy method in this paper. It shows that the capillary potential energy of the atomization droplets is supplied by the impingement of the gas on the liquid. The energy crite...Gas atomization has been studied by using energy method in this paper. It shows that the capillary potential energy of the atomization droplets is supplied by the impingement of the gas on the liquid. The energy criterion of the minimum equivalent diameter of the atomization droplets is obtained. The result is comparable to the empirical formulae.[HJ*2/3]展开更多
Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimi...Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimizing the geometric parameters of delivery tube outlet and gas outlet to obtain applicable atomization scale parameters. A computational fluid flow model is adopted to investigate the effect of atomization gas pressure ( P0 ) on the gas flow field in gas atomization progress. The numerical results show that the outlet gas velocity of the nozzle is not affected by P0 and the maximum gas velocity reaches 452 m / s. The alternation of aspiration pressure ( ΔP) is caused by the variations of stagnation pressure and location of Mach shock disk, and hardly by the location of stagnation point. The aspiration pressure is found to decrease as P0 increases when P0 < 1. 3 MPa. However,at a higher atomization gas pressure increasing P0 causes an opposite: the aspiration pressure atomization increases with the gas pressure,and keeps a plateau when P0 > 2. 0 MPa. The minimum aspiration pressure ΔP = - 70 kPa is obtained at P0 = 1. 3 MPa. The results indicate that the designed Laval- style annual slot nozzle has well atomization characteristic at lower atomization pressure.展开更多
Alnico powders were prepared by gas atomization process. Composition of the Alnico powders was Fe37.1 A18.2Ni17.6-Co26.6 Cu3.3 Ti7.2 (wt pct) which was the same as that of commercially available Alnico magnets. Averag...Alnico powders were prepared by gas atomization process. Composition of the Alnico powders was Fe37.1 A18.2Ni17.6-Co26.6 Cu3.3 Ti7.2 (wt pct) which was the same as that of commercially available Alnico magnets. Averageparticle size of the powders was 119μm. Effects of heat treatment in magnetic field on magnetic properties of thepowders were investigated. The optimum process of heat treatment was found as follows, heated at 870℃ for 1min first, then cooled down to 700℃ at cooling rate 0.3℃/s in magnetic field, and finally aged isothermally for 4 h.Magnetic properties of the Alnico powders were measued and the results were that intrinsic coercivity i_H_c was 1.0kOe and remanence M_r was 36.5 emu/g.展开更多
The gas flow in the Hartmann resonance tube is numerically investigated by the finite volume method based on the Roe solver. The oscillation of the flow is studied with the presence of a needle actuator set along the ...The gas flow in the Hartmann resonance tube is numerically investigated by the finite volume method based on the Roe solver. The oscillation of the flow is studied with the presence of a needle actuator set along the nozzle axis. Numerical results agree well with the theoretical and experimental results available. Numerical results indicate that the resonance mode of the resonance tube will switch by means of removing or adding the actuator. The gas flow in the ultrasonic gas atomization (USGA) nozzle is also studied by the same numerical methods. Oscillation caused by the Hartmann resonance tube structure, coupled with a secondary resonator, in the USGA nozzle is investigated. Effects of the variation of parameters on the oscillation are studied. The mechanism of the transition of subsonic flow to supersonic flow in the USGA nozzle is also discussed based on numerical results.展开更多
In this paper, the flow fields of three types of nozzles ( Hartmann, Laval and Laminar nozzles ) under the same conditions are simulated, and the corresponding to pressure, temperature, velocity and turbulence inten...In this paper, the flow fields of three types of nozzles ( Hartmann, Laval and Laminar nozzles ) under the same conditions are simulated, and the corresponding to pressure, temperature, velocity and turbulence intensity are obtained. The results suggest that two crushing presents in the atomization process using Hartmann nozzle, but only one crushing presents in the atomization process using the other nozzles, through the comparative research on the flow field features of three types of nozzle. Furthermore, the shockwave plays a more important role in crushing of liquid metal than velocity.展开更多
文摘A Laval-type supersonic gas atomizer was designed for low-pressure gas atomization of molten metals. The principal design ob-jectives were to produce small-particle uniform powders at lower operating pressures by improving the gas inlet and outlet structures and op-timizing structural parameters. A computational fluid flow model was developed to study the flow field characteristics of the designed atom-izer. Simulation results show that the maximum gas velocity in the atomization zone can reach 440 m&#183;s-1;this value is independent of the atomization gas pressure P0 when P0〉0.7 MPa. When P0=1.1 MPa, the aspiration pressure at the tip of the delivery tube reaches a mini-mum, indicating that the atomizer can attain the best atomization efficiency at a relatively low atomization pressure. In addition, atomization experiments with pure tin at P0=1.0 MPa and with 7055Al alloy at P0=0.8 and 0.4 MPa were conducted to evaluate the atomization capa-bility of the designed atomizer. Nearly spherical powders were obtained with the mass median diameters of 28.6, 43.4, and 63.5μm, respec-tively. Compared with commonly used atomizers, the designed Laval-type atomizer has a better low-pressure gas atomization capability.
基金the National Natural Science Foundation of China(Grant No.51975240)the Open Fund of State Key Laboratory of Advanced Forming Technology and Equipment(Grant No.SKL2019006).
文摘The paper aims at modeling and simulating the atomization process of the close-coupled ring-hole nozzle in vacuum induction gas atomization(VIGA)for metallic powder production.First of all,the primary atomization of the ring-hole nozzle is simulated by the volume of fluid(VOF)coupled large eddy simulation(LES)model.To simulate the secondary atomization process,we use the method of selecting the droplet sub-model and the VOF model.The results show that the ring-hole nozzle forms a gas recirculation zone at the bottom of the delivery tube,which is the main reason for the formation of an annular liquid film during the primary atomization.In addition,the primary atomization process of the ring-hole nozzle consists of three stages:the formation of the serrated liquid film tip,the appearance and shedding of the ligaments,and the fragmentation of ligaments.At the same time,the primary atomization mainly forms spherical droplets and long droplets,but only the long droplets can be reserved and proceed to the secondary atomization.Moreover,increasing the number of ring holes from 18 to 30,the mass median diameter(MMD,d_(50))of the primary atomized droplets decreases first and then increases,which is mainly due to the change of the thickness of the melt film.Moreover,the secondary atomization of the ring-hole nozzles is mainly in bag breakup mode and multimode breakup model,and bag breakup will result in the formation of hollow powder,which can be avoided by increasing the gas velocity.
基金This work has been supported by the Flu,tda~ion Of harbin institute of Technology for Out standing YOungScientists (No. 1832).
文摘A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the alloy was very fine and its microstructure was mainly consisted of Si crystals plus intermetallic compound A19FeSi3, which were.very fine and uniformly distributed.
基金financially supported by the National High-Tech Research and Development Program of China (No. 2009AA033901)the National Natural Science Foundation of China (No. 51004019)
文摘17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy (SEM), and the X-ray diffraction (XRD) technique. The results show that the mass median particle diameter is about 19.15 prn. Three main types of surface microstructures are observed in the powders: well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.
文摘The crucible-free electrode induction melting gas atomization(EIGA) technology is an advanced technology for preparing ultra-clean nickel-based superalloy powders. One of the key issues for fabricating powders with high quality and yield is the consecutive induction melting of a superalloy electrode. The coupling of a superalloy electrode and coil,frequency, output power, and heat conduction are investigated to improve the controllable electrode induction melting process. Numerical simulation results show that when the coil frequency is 400 kHz, the output power is 100 kW, superalloy liquid flow with a diameter of about 5 mm is not consecutive. When the coil frequency is reduced to 40 kHz, the output power is 120 kW, superalloy liquid flow is consecutive, and its diameter is about 7 mm.
基金Funded by the National Natural Science Foundation of China(Nos.U1502274 and 51834009)。
文摘2wt%TiB_(2)/Cu composite powders were fabricated in situ by reactive gas atomization.The fabricated composite powder exhibits high sphericity,and the powder sizes range from 5μm to 150μm.The morphology of the Cu matrix and the distribution of the TiB2 particles in the composite powders vary with the powder size.The critical transitions of interface morphologies from dendritic-to-cellular and cellular-to-planar interfaces occurs when the composite powder sizes decrease to 34μm and 14μm,respectively.Compared with pure Cu droplets,the composite droplets undergo critical transition of the interface morphologies at a smaller droplet size corresponding to a higher cooling rate because the existence of TiB2 particles can cause instability in the advancing solidification front and heterogeneous nucleation.With decreasing powder size,the extent of the TiB_(2) particle interdendritic segregation decreases as the result of enhanced engulfment of TiB2 particles by the advancing solidification front.
文摘Super-clean and super-spherical FGH4095 superalloy powder is produced by the ceramic-free electrode inductionmelt inert gas atomization(EIGA) technique.A continuous and steady-state liquid metal flow is achieved at high-frequency(350 k Hz) alternating current and high electric power(100 k W).The superalloy is immersed in a high-frequency induction coil,and the liquid metal falling into a supersonic nozzle is atomized by an Ar gas of high kinetic gas energy.Numerical calculations are performed to optimize the structure parameters for the nozzle tip.The undesired oxidation reaction of alloying elements starts at 1000℃ with the reaction originating from the active sites on the powder surfaces,leading to the formation of oxides,MexOy.The role of active sites and kinetic factors associated with the diffusion of oxygen present in the atomization gas streams are also examined.The observed results reveal that the oxidation process occurring at the surface of the produced powders gradually moves toward the core,and that there exists a clear interface between the product layer and the reactant.The present study lays a theoretical foundation for controlling the oxidation of nickel-based superalloy powders from the powder process step.
基金supported by the National Natural Science Foundation of China (Grant Nos.10772107, 10702038)the Shanghai Municipal Key Projects on Basic Research (Grant No.08JC1409800)+1 种基金the Innovation Project of Shanghai Municipal Education Commission (Grant No.08YZ10)the Shanghai Municipal Science and Technology Commission (Grant No.09DZ1141502)
文摘The resonant behaviors of an ultra-sonic gas atomization nozzle with a zero mass-flux jet actuator were numerically investigated with FLUENT software by using a double precision unsteady two-dimensional pressure-based solver. The Spalart-Allmaras turbulence model was adopted in the simulations. Numerical results indicated that the oscillation properties of the gas efflux were effectively improved. Several resonatory frequencies corresponding to different vibration modes of gas were distinguished in the nozzle. With the changing of nozzle geometric parameters, different characters among those modes were elucidated by analyzing the propagations of pressure waves.
基金the Major State Ba-sic Research Development Program of China (Nos. 2006CB605203 and 2006CB605204)
文摘Al-20Sn-1Cu powders were prepared by gas atomization in an argon atmosphere with atomizing pressures of 1.1 and 1.6 MPa. The characteristics of the powders are determined by means of dry sieving, scanning electron microscopy (SEM), optical microscopy (OM), and X-ray diffractometry (XRD). The results show that the powders exhibit a bimodal size distribution and a higher gas pressure results in a broad size distribution. All particles in both cases are spherical or nearly spherical and satellites form on the surface of coarse particles. Dendritic and cellular structures coexist in the particle. With decreasing particle diameter, the secondary dendrite arm spacing (SDAS) decreases and the cooling rate increases. The particles processed under high gas atomization pressure (1.6 MPa) exhibit a lower SDAS value and a higher cooling rate than those of the same size under low gas atomization pressure (1.1 MPa). The XRD results show that the Sn content increases with decreasing particle size.
基金the National Basic Research Program of China (No. 2011CB012902) for their continuing support to this research
文摘In this study, the microstructure evolution of rapidly solidified ASP30 high-speed steel particles was predicted using a simulation method based on the cellular automaton-finite element (CAFE) model. The dendritic growth kinetics, in view of the characteristics of ASP30 steel, were calculated and combined with macro heat transfer calculations by user-defined functions (UDFs) to simulate the microstructure of gas-atomized particles. The relationship among particle diameter, undercooling, and the convection heat transfer coefficient was also inves- tigated to provide cooling conditions for simulations. The simulated results indicated that a columnar grain microstructure was observed in small particles, whereas an equiaxed microstructure was observed in large particles. In addition, the morphologies and microstructures of gas-atomized ASP30 steel particles were also investigated experimentally using scanning electron microscopy (SEM). The experimental re- suits showed that four major types ofmicrostructures were formed: dendritic, equiaxed, mixed, and multi-droplet microstructures. The simu- lated results and the available experimental data are in good agreement.
基金supported by the National Key Research and Development Program of China(No.2016YFB1100204)the Key Research&Development Plan of Jiangxi Province(No.20192ACB80001)the National Natural Science Foundation of China(Nos.52171163,51701214 and U1908219)。
文摘Gas atomization is now an important production technique for Fe-based amorphous alloy powders used in additive manufacturing,particularly selective laser melting,fabricating large-sized Fe-based bulk metallic glasses.Using the realizable k-εmodel and discrete phase model theory,the flow dynamics of the gas phase and gas-melt two-phase flow felds in the close-wake condition were investigated to establish the correlation between high gas pressure and powder particle characteristics.The locations of the recirculation zones and the shapes of Mach disks were analyzed in detail for the type of discrete-jet closed-coupled gas atomization nozzle.In the gas-phase flow feld,the vortexes,closed to the Mach disk,are found to be a new deceleration method.In the two-phase flow feld,the shape of Mach disk changes from“S”-shape to“Z”-shape under the impact of the droplet flow.As predicted by the wave model,with the elevation of gas pressure,the size of the particle is found to gradually decrease and its distribution becomes more concentrated.Simulation results were compliant with the Fe-based amorphous alloy powder preparation tests.This study deepens the understanding of the gas pressure impacting particle features via gas atomization,and contributes to technological applications.
文摘The instability theory of fluid flow is applied in gas atomization and the results show that the instability of interfacial wave is the main cause of gas atomization. The size of the droplets and its change with parameters are also studied, the results are compatible with the experiments.
基金financially supported by the Industrielle Gemeinschaftsforschung IGF(Grant No.19219 N/1)the Japan Society for the Promotion of Science(Grant No.18K04767)+1 种基金V.Uhlenwinkel and L.Madler also greatly acknowledge funding from the Deutsche Forschungsgemeinschaft(DFG)-Project(No.276397488-SFB 1232)for partly supporting this researchthe financial support through the following scholarships:MAPEX Center for Materials and Processes at the University of Bremen and the Cooperative Research and Development Center for Advanced Materials at Tohoku University(No.GIMRT-18GK0015)。
文摘Processing soft ferromagnetic glass-forming alloys through gas atomization and consolidation is the most effective technique to produce bulk samples.The commercial viability of these materials depends on commercial purity feedstock.However,crystallization in commercial purity feedstock is several orders of magnitude faster than in high purity materials.The production of amorphous powders with commercial purity requires high cooling rates,which can only be achieved by extending the common process window in conventional gas atomization.The development of novel cooling strategies during molten metal gas atomization on two model alloys({(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 and Fe76B10Si9P5)is reported.Hydrogen inducement during liquid quenching significantly improved the glass-forming ability and soft magnetic properties of{(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 powders.Spark plasma sintering experiments verified that amorphous rings could be produced regardless of the cooling strategies used.While the saturation magnetization was almost unaffected by consolidation,the coercivity increased slightly and permeability decreased significantly.The magnetic properties of the final bulk samples were independent of feedstock quality.The developed cooling strategies provide a great opportunity for the commercialization of soft ferromagnetic glass-forming alloys with commercial purity.
基金the financial supports from the National Natural Science Foundation of China(Grant Nos.51301157 and 51434007)the National High Technology Research and Development Program of China 863 Program(Grant No.2013AA031103)
文摘The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperature range of 1323-1473 Kand strain rate range of 0.001-0.5s^(-1).The calculated activation energy in the above variational ranges of temperature and strain rate possesses a low activation energy value of approximately 365.6kJ/mol based on the constitutive relationship models developed with the Arrhenius-type constitutive model respectively considering the strain rate and deformation temperature.The hot working flow behavior during the deformation process was analyzed combined with the microstructural evolution.Meanwhile,the processing maps during the deformation process were established based on the dynamic material model and Prasad instability criterion under different deformation conditions.Finally,the optimal hot processing window of this alloy corresponding to the wide temperature range of 1353-1453 Kand the low strain rate of 0.001-0.1s^(-1) was obtained.
文摘Microstructure, thermodynamics and electrochemicalproperties of novel RE (NiAlCu)x(x= 4.5, 4.9, 5.6 ) microcrystalline hydrogen-storage alloy powder prepared by gas atomization wasinvestigated. It indicates that alloyparticles show relatively regularspherical. Microstructure is composed of the AB5 matrix phase andeutectic double-phase structure withthe AB5 phase and Ni3Al along grainboundaries when x = 5. 6, there is acoexistent structure consisting ofAB5 phase and eutectic doublephase with AB3 and AB phases along grain boundaries at x= 4.5.When x is increased to 4.9, themixed structures are composed ofAB5 and a few AB phases in discontinuous network distribution. Theelectrochemical capacity of alloy is210~300 mAh·g-1, and the activated periods are only 1~3 times.lt seems to be ascribed to the appearance of a great number of freshsurfaces within powder particles resulting from the as-quenched microcrack along the interphase boundaries within particles propagatinggradually in the process of hydrogen-absorption-and dissociation dueto the intrinsic double-phase structure.
文摘Gas atomization has been studied by using energy method in this paper. It shows that the capillary potential energy of the atomization droplets is supplied by the impingement of the gas on the liquid. The energy criterion of the minimum equivalent diameter of the atomization droplets is obtained. The result is comparable to the empirical formulae.[HJ*2/3]
文摘Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimizing the geometric parameters of delivery tube outlet and gas outlet to obtain applicable atomization scale parameters. A computational fluid flow model is adopted to investigate the effect of atomization gas pressure ( P0 ) on the gas flow field in gas atomization progress. The numerical results show that the outlet gas velocity of the nozzle is not affected by P0 and the maximum gas velocity reaches 452 m / s. The alternation of aspiration pressure ( ΔP) is caused by the variations of stagnation pressure and location of Mach shock disk, and hardly by the location of stagnation point. The aspiration pressure is found to decrease as P0 increases when P0 < 1. 3 MPa. However,at a higher atomization gas pressure increasing P0 causes an opposite: the aspiration pressure atomization increases with the gas pressure,and keeps a plateau when P0 > 2. 0 MPa. The minimum aspiration pressure ΔP = - 70 kPa is obtained at P0 = 1. 3 MPa. The results indicate that the designed Laval- style annual slot nozzle has well atomization characteristic at lower atomization pressure.
文摘Alnico powders were prepared by gas atomization process. Composition of the Alnico powders was Fe37.1 A18.2Ni17.6-Co26.6 Cu3.3 Ti7.2 (wt pct) which was the same as that of commercially available Alnico magnets. Averageparticle size of the powders was 119μm. Effects of heat treatment in magnetic field on magnetic properties of thepowders were investigated. The optimum process of heat treatment was found as follows, heated at 870℃ for 1min first, then cooled down to 700℃ at cooling rate 0.3℃/s in magnetic field, and finally aged isothermally for 4 h.Magnetic properties of the Alnico powders were measued and the results were that intrinsic coercivity i_H_c was 1.0kOe and remanence M_r was 36.5 emu/g.
文摘The gas flow in the Hartmann resonance tube is numerically investigated by the finite volume method based on the Roe solver. The oscillation of the flow is studied with the presence of a needle actuator set along the nozzle axis. Numerical results agree well with the theoretical and experimental results available. Numerical results indicate that the resonance mode of the resonance tube will switch by means of removing or adding the actuator. The gas flow in the ultrasonic gas atomization (USGA) nozzle is also studied by the same numerical methods. Oscillation caused by the Hartmann resonance tube structure, coupled with a secondary resonator, in the USGA nozzle is investigated. Effects of the variation of parameters on the oscillation are studied. The mechanism of the transition of subsonic flow to supersonic flow in the USGA nozzle is also discussed based on numerical results.
文摘In this paper, the flow fields of three types of nozzles ( Hartmann, Laval and Laminar nozzles ) under the same conditions are simulated, and the corresponding to pressure, temperature, velocity and turbulence intensity are obtained. The results suggest that two crushing presents in the atomization process using Hartmann nozzle, but only one crushing presents in the atomization process using the other nozzles, through the comparative research on the flow field features of three types of nozzle. Furthermore, the shockwave plays a more important role in crushing of liquid metal than velocity.