Gas Atomization Process Research Articles

Compositional Optimization of In718 Superalloy Powder for Additive Manufacturing

In this research, a composition optimized In718 superalloy powder suitable for additive manufacturing has been developed by using the vacuum induction melting gas atomization (VIGA) and the powder sieving process. VIGA which combines the vacuum induction melting (VIM) and gas atomization (GA) processes uses high pressure inert gas to atomize the metal melt formed by VIM to form metal droplets. These metal droplets are solidified to form metal powders during the falling process in the atomized chamber. After the sieving process, the mean particle size D50 of the powder is less than 35 μm and the particle size distribution (PSD) ranges from 10 to 55 μm (D10~D90). Besides, the produced powder has high flowability (ICarr ≦15), which is suitable for selective laser melting (SLM) additive manufacturing (AM). After the SLM process, the tensile tests are conducted at room temperature and high temperature of 650°C. The results show that the high temperature properties of the optimized In718 superalloy are superior to the commercial In718 superalloy.

Laser Additive Manufacturing of (Ti-6Al-4V)/10 wt.% Ag Composite Using Spherical Powders to Reduce Wear and Friction

In order to extend the service lifetime of Ti-6Al-4V-based components, friction and wear behaviors of Ti-6Al-4V alloys needed to be further improved. Laser additive manufacturing with a moving laser beam was used to prepare (Ti-6Al-4V)/10 wt.% Ag samples, on a three-dimensional RC-SLM400 printer with laser powers of 2-10 kW. (Ti-6Al-4V)/10 wt.% Ag samples were successfully printed using spherical powders prepared by gas atomization process (SPGAP) and combustion reaction (SP-CR). The tribological properties of the as-prepared samples sliding against Si3N4 balls were examined using a ball-on-disk tribometer. The results showed that the tribological behavior of (Ti-6Al-4V)/10 wt.% Ag printed by SP-CR was better than that of the sample printed by SPGAP. The low friction and reduced wear were mainly attributed to the formation of the lubrication layer containing large amounts of silver, which can exhibit an excellent deformation and plastic ductility. It effectively reduced the friction resistance and material loss and provided the good lubrication for 0-80 min, resulting in low friction and reduced wear of the samples prepared by SP-CR.

Study on the flowability of TC4 Alloy Powder for 3D Printing

The flowability of metal powder is an important factor that can affect the quality of printing metal parts in powder bed, which has a significant effect on the quality of 3D printed parts. In this paper, the commercial TC4 powder prepared by plasma atomization (PA), Electrode Induction-melting inert Gas Atomization (EIGA) and plasma rotation electrode process (RFP) was used as the research object. The traditional static flow test method and FT4 powder rheometer were used to test the dynamic performance of TC4 powder. The flowability properties of powder materials are characterized by the combination of integral properties and Dynamic rheological properties to determine the more important powder flowability parameters for 3D printing and to provide a theoretical reference for the preliminary screening of powder for printing. The results show that the particle size, particle size distribution, particle surface finish and particle size uniformity have great influence on the flowability, but the effect of particle size composition on the apparent density is not a single value. The powder sample with good surface finish and uniform particle size has good flowability. The basic flow energy of the powder sample produced by PA is small, the shear stress between the powder layers is small, and it is easy to slide, but not easy to improve the flowability of powder by aeration. The basic flow energy of powder samples produced by EIGA is the highest. Powder compressibility is the worst. Its air permeability is not good, the wall friction action is small, is not easy to adhere. The effect of vibration on the flowability of powder is small. The basic flow energy of the powder samples produced by RFP is smaller because of its large particle size and better sphericity. The compressibility and permeability of the powder are better. The shear action between the powder layer and the interlayer and the friction on the wall are smaller and the relative viscosity is weaker. The powder is insensitive to the flow rate, and the effect of vibration on the flowability is relatively small.

Printability of gas atomized Mo-Si-B powders by laser metal deposition

Mo-Si-B alloys, as a more and more frequently considered high-temperature material, face the challenge of machining complex shapes. In the present work, the feasibility of printing pre-alloyed Mo-Si-B powder materials via laser metal deposition (LMD) process was firstly demonstrated. Mo-Si-B powder was manufactured via gas atomization (GA) process out of solid raw materials meeting the requirements for additive manufacturing (AM) regarding flowability and particle size. Investigations of the powder particles after GA and detailed analyses of the printability and microstructural evolution of the multi-phase Moss-Mo3Si-Mo5SiB2 built are presented. As a result, distinct zones resulting from the layer-wise LMD process were observed next to a microstructure of primarily solidified Moss phases embedded in fine dispersed eutectic regions. The hardness of the LMD processed material is shown to be comparable with Mo-Si-B alloys produced by ingot metallurgy (IM).

A model for the drag and heat transfer of spheres in the laminar regime at high temperature differences

Modern powder metallurgical processes such as additive manufacturing or metal injection molding require metal powders with specific properties, which are commonly produced by gas atomization processes. Modeling of cooling and solidification of molten metal droplets requires the knowledge of the droplet and particle motion and heat transfer. While there are correlations for drag and heat transfer of spheres at isothermal conditions or temperature differences between droplet and gas smaller than 200 K, knowledge for temperature differences as high as 1000 K is limited. In this work, we first critically review common correlations for the drag coefficient and Nusselt number of spheres and develop a computational model to solve the non-isothermal flow for such conditions. After validation, new correlations are benchmarked against computational experiments. While we could confirm a good agreement for the Nusselt number correlations, we develop a novel temperature-dependent correction for the drag coefficient in the laminar regime. This correlation is based on data for 1 < Re < 130 for two different ideal gases.

Portable water-using H2 production materials converted from waste aluminum

ABSTRACTThis study investigates the feasibility of using waste aluminum as a substitute to pure aluminum for preparing portable water-using hydrogen production materials by gas atomization process. The H2 production performances of waste aluminum H2 production materials in different reaction conditions considering reaction temperature, reaction aqueous solution and water adding method were investigated. The results show that such materials can achieve a high Al/H2 conversion and a stable H2 flow rate for practical fuel cell electricity generation. In addition, the recycling of activation agents and Al(OH)3 can be realized.

Study of Effect of Metal Delivery Tube on Flow characteristics of Fluids and Melt in Convergent- Divergent nozzle used for Gas Atomization Process using CFD techniques

Study of Effect of Metal Delivery Tube on Flow characteristics of Fluids and Melt in Convergent- Divergent nozzle used for Gas Atomization Process using CFD techniques

The Effect of Microstructure on the Electrical Properties of Gas-Atomized Copper–Iron Metastable Alloys

With the increase in global demand for highly functionalized materials, there is continued interest in exploiting the material properties of metals either individually or in the form of alloys. Copper–iron alloy is considered unique with its remarkable combination of strength and high electrical conductivity. Due to the low cost of iron, this alloy is expected to replace alloys like Cu–Ag and Cu–Nb. In order to explore the microstructural features, copper–iron alloy with three different compositions (10, 30, and 50 at.% Fe) were prepared by a gas atomization process. A detailed microstructural characterization was performed using scanning electron microscopy, X-ray diffraction, and electron backscattered diffraction. Spark plasma sintering was used to sinter the powders to evaluate their electrical conductivities. The mechanism of the microstructure formation is also discussed in detail. As the Fe content increases, the Fe-rich phase changes its shape from spherical to irregular with a concomitant sharp decrease in the electrical conductivity of the alloy.

Effect of composition and powder size on magnetic properties of rapidly solidified copper-iron alloys

Powders of copper-iron alloys with composition of 10, 30 and 50 at% Fe were prepared by gas atomization process, sintered by Spark Plasma Sintering. The analysis of the as synthesized sample shows two phase FCC-Cu and BCC-Fe structure in all the three compositions independent of powder size. However, solid solution was formed between Cu and Fe during rapid solidification stages. Samples of CFA measuring ≤24 μm exhibited higher magnetic saturation (Ms) as compared to larger powder particles of the same composition due to the presence of enhanced amount of solid solution. With the increase in Fe contents, Ms and coercivity of the alloy both increase.

Computational fluid dynamic investigation of the primary and secondary atomization of the free-fall atomizer in electrode induction melting gas atomization process

Nickel-based superalloy is mainly used for fabricating the important high temperature parts including the turbine disk, turbine baffle, compressor disk, and other critical components. Ceramic inclusions in powder metallurgy (PM) superalloy could promote fatigue crack initiation, and thus accelerating the crack propagation under certain conditions. In this case, the ultra-clean nickel-based superalloy powder is critical for PM superalloy components. Generally, there are two well-known methods of fabricating superalloy powders, i.e., argon gas atomization (AA) and plasma rotating electrode process (PREP). Electrode induction melting gas atomization (EIGA) process is a newly developed method of preparing ultra-clean metal powders. The EIGA process is a completely crucible-free melting and atomization process developed by ALD vacuum technologies. In this process, a slowly rotating prealloyed bar is fed into a conical induction coil. The end of the bar is inductively heated and molten alloys falls into an atomizer where the liquid alloy is atomized with a high-pressure inert gas. The EIGA prepared powders possess the advantages of AA (more fine powders) and PREP (ultra-clean powders) processes. Generally, there are two key issues in EIGA process, and the free-fall gas atomizer design is one of the critical issues for the powder yield and quality. Free-fall gas atomizers are some of the first two fluid atomizer designs to be used for molten metal atomization. In a simple open (unconfined stream) design a melt stream falls from a tundish exit via gravity into the convergence of focused atomization gas jets where it is disintegrated. The gas-melt interaction is complex, and it is difficult to characterize the interaction process directly. To have a good understanding of the atomisation technology, the physical break-up process instead of correlating the gas dynamics with droplet fragmentation indirectly must be able to be examined. And it will be desirable, if we input the atomization parameters, we can obtain the particles' distributions directly. In this work, a computational fluid dynamic approach to simulating the primary and secondary atomization processes is developed by using the volume of fluid method and discrete phase model. By integrating the metal stream break-up (in primary atomization) with the flow field and particles distribution simulation (in second atomization), this numerical simulation method is able to provide the direct assessment for the atomisation process. To verify the method performance, the melt stream is initialized into a 4 mm-diameter stream, which is then injected into the gas flow field for further fragmentation. The experimental results show that the simulated particles' diameter distribution is consistent with the experimental results in the same conditions.

Additive manufacturing of NiTiHf high temperature shape memory alloy

A NiTi-20Hf high temperature shape memory alloy (HTSMA) was additively manufactured by selective laser melting (SLM) technique using NiTiHf powder. The thermomechanical and shape memory response were compared to the conventional vacuum induction skull melted counterpart. Transformation temperatures of the SLM material were found to be above 200°C and slightly lower due to the additional oxygen pick up from the gas atomization and melting process. The shape memory response in compression was measured for stresses up to 500MPa, and transformation strains were found to be very comparable (up to 1.26% for as-extruded; up to 1.52% for SLM).

Nucleation and microstructure development in Cr-Mo-V tool steel during gas atomization

Nucleation studies of undercooled metallic melts are of essential interest for the understanding of phase selection, growth kinetics and microstructure development during their rapid non-equilibrium solidification. The paper deals with the modelling of nucleation processes and microstructure development in the hypoeutectic tool steel Ch12MF4 with the chemical composition of 2.37% C, 12.06 % Cr, 1.2% Mo, 4.0% V and balance Fe [wt. %] in the process of nitrogen gas atomization. Based on the classical theory of homogeneous nucleation, the nucleation temperature of molten rapidly cooled spherical particles from this alloy with diameter from 40 μm to 600 μm in the gas atomization process is calculated using various estimations of parameters influencing the nucleation process – the Gibbs free energy difference between solid and liquid phases and the solid/liquid interfacial energy. Results of numerical calculations are compared with experimentally measured nucleation temperatures during levitation experiments and microstructures developed in rapidly solidified powder particles from the investigated alloy.

Effect of lattice strain on the electrical conductivity of rapidly solidified copper-iron metastable alloys

Copper–iron alloys (CFAs) with composition CFAX; x = 10, 30 and 50 at% Fe were prepared by gas atomization process, sintered and heat treated in vacuum. Rapid solidification and the incorporation of Fe into Cu hint at strain generation in the lattice bringing changes in electrical conductivity. The origin of this strain is discussed using structural and electrical properties. The substitutional solid solution formed between Cu and Fe due to rapid solidification was decomposed during heat treatment in all the three compositions, followed by the increase in Fe particle size, decrease in lattice strain and increase in electrical conductivity.

Preparation of high-entropy AlCoCrCuFeNiSi alloy powders by gas atomization process

High-entropy Al0.5CoCrCuFeNi, Al0.5CoCrCuFeNiSi1.2 and Al0.5CoCrCuFeNiSi2.0 alloy powders were successfully prepared by gas atomization process. All alloy powders have spherical shapes with smooth surfaces. The median particle size distribution D50 is about 27 μm for different alloy compositions. With the addition of silicon, the fast cooling rate of gas atomization process reduce segregation, together with the solid solution strengthening effect increases the hardness of powders from 200.5 to 751.8 Hv without reducing the crystallinity of the alloy. The high-entropy alloy powders which prepared by gas atomization process can be potentially used for additive manufacturing applications.

Microstructural transformation and thermo-mechanical improvement of quinary Bi–Sn–In–Ga–Zn solder bumps on a flexible PET substrate

Novel Bi–Sn–In–Ga–Zn powders were fabricated using a gas atomization process. The addition of 5.0wt% Zn to a Bi–Sn–In–Ga alloy system resulted in the formation of a pure Zn state as a precipitate, which was mostly dispersed along the grain boundaries during solidification. From this reason, the refined microstructure, which was effective for easy adsorption of outer thermal energy and high surface free energy, could provide a lower onset melting temperature of 58.9°C and narrower melting range of 6.9°C compared to those of the quaternary solder powders used as a reference (61.6 and 7.6°C, respectively). The hardness of the quinary solder was also significantly increased (by 34.7%) by the addition of Zn. As a result, the quinary solder pastes reflowed at a low melting temperature of 110°C, which is well suited to the formation of solder joints on a flexible polyethylene terephthalate (PET) substrate.

Microstructures of Powders and Additively Manufactured Objects of an Alloy Tool Steel for Cold-Work Dies

A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich ...

Influence of Powder Characteristics on Formation of Porosity in Additive Manufacturing of Ti-6Al-4V Components

This paper aims to study the genesis of defects in titanium components made through two different additive manufacturing technologies: selective laser melting and electron beam melting. In particular, we focussed on the influence of the powders used on the formation of porosities and cavities in the manufactured components. A detailed experimental campaign was carried out to characterize the components made through the two additive manufacturing techniques aforementioned and the powders used in the process. It was found that some defects of the final components can be attributed to internal porosities of the powders used in the manufacturing process. These internal porosities are a consequence of the gas atomization process used for the production of the powders themselves. Therefore, the importance of using tailored powders, free from porosities, in order to manufacture components with high mechanical properties is highlighted.

Effect of Atomization Parameters on Size and Morphology of Al-17Si Alloy Powder Produced by Free Fall Atomizer

Abstract: In the present work the effect of process parameters on the characteristics of Al-17Si alloy powder produced by gas atomization using a free fall nozzle of different apex angles. The axial gas velocity away from the nozzle exit is measured for different operating pressures. The alloy was melted to a superheat temperature of 100,150 and 200° C and atomized by varying the gas flow rate and melt flow rate. The powder produced during gas atomization process generally exhibits a wide size distribution. ASTM standard sieve with vibratory shaker is used for powder analysis. The characterization of powder particles was accomplished by the parameters such as mass median, average size of powder particles; standard deviation and morphology of powder were studied by scanning electron microscopy. It is observed that decrease of apex angle results in axial velocity decreases in entire applied gas pressures range. Increase in apex angle results in decrease of gas jet length to metal stream collision, the median particle diameter of the powder increases resulting in decrease in particle irregularity. The median particle diameter of the powder has been shown to decrease almost linearly with increase in gas to melt flow (G/M) ratio. The sauter mean diameter variation, however, decreases slowly with increase in G/M ratio. Median particle diameter is significantly reduced with increase in the melt superheat.

Porosity, Microstructure, and Mechanical Properties of Ti-6Al-4V Alloy Parts Fabricated by Powder Compact Forging

Ti-6Al-4V alloy powders produced using a hydrogenation–dehydrogenation process and a gas atomization process, respectively, were rapidly consolidated into near-net-shaped parts by powder compact forging. The porosity, microstructure, and tensile mechanical properties of specimens cut from regions at different distances from the side surfaces of the forged parts were examined. The regions near the side surfaces contained a fraction of pores due to the circumferential tensile strain arising during the powder compact forging process, and the porosity level decreased rapidly to zero with increasing the distance from the side surface. The forged parts had a fully lamellar structure with the α + β colony sizes and α lamella thickness changing little with the distance from the side surface. The specimens cut from the regions near the side surfaces had a lower yield strength and tensile strength. The correlation of porosity with the yield strength of the specimens suggested that the reduction of load bearing areas due to the porosity and unbonded or weakly bonded interparticle boundaries was not the only reason for the lower strength, and the stress concentration at the pores and associated with their geometry also played an important role in this. It is likely that the effect of stress concentration on yield strength reduction of the forged part increases with oxygen content. The Hall–Petch relationship of the yield strength and the average α lamella thickness suggested that the strength of the fully dense and fully consolidated forged parts was increased by oxygen solution strengthening.

Characteristics of 7055Al alloy powders manufactured by gas-solid two-phase atomization: A comparison with gas atomization process

In this paper, the principle of gas-solid two-phase atomization methodology for metal powder is demonstrated. A cost-effective production technology for high-quality metal powder was proposed. The morphology, size distribution, microstructure and cooling rate of two-phase atomized 7055Al powder were examined. The experimental results have demonstrated a number of advantages and unique features of gas-solid two-phase atomization in the preparation of metal powders. When the Argon gas pressure P=0.6MPa and iron particle feed rate M′=235.6g·min−1, the mass median diameter (d50) of the 7055Al powder manufactured by two-phase atomization process was 22.8μm, which is reduced by 52.7% compared with gas atomized powders with d50=48.2μm under the same atomization parameters. Experimental results also showed that the gas-solid two-phase atomized powders exhibited more irregular shapes than gas atomized powders. The cooling rate of most powders was in the range of 104–105K/s, and for some extra checked fine powders the cooling rate can even reach 106K/s. The two-phase atomized powders had larger cooling rate and presented obvious rapid solidification characteristics than gas atomized powder with the same diameter. Moreover, this study indicates that gas-solid two-phase atomization could be a promising high-quality and low-cost metal powder preparation technology.