Gas Atomization Process Research Articles

Life cycle assessment of metal powder production: a Bayesian stochastic Kriging model-based autonomous estimation

Metal powder contributes to the environmental burdens of additive manufacturing (AM) substantially. Current life cycle assessments (LCAs) of metal powders present considerable variations of lifecycle environmental inventory due to process divergence, spatial heterogeneity, or temporal fluctuation. Most importantly, the amounts of LCA studies on metal powder are limited and primarily confined to partial material types. To this end, based on the data surveyed from a metal powder supplier, this study conducted an LCA of titanium and nickel alloy produced by electrode-inducted and vacuum-inducted melting gas atomization, respectively. Given that energy consumption dominates the environmental burden of powder production and is influenced by metal materials’ physical properties, we proposed a Bayesian stochastic Kriging model to estimate the energy consumption during the gas atomization process. This model considered the inherent uncertainties of training data and adaptively updated the parameters of interest when new environmental data on gas atomization were available. With the predicted energy use information of specific powder, the corresponding lifecycle environmental impacts can be further autonomously estimated in conjunction with the other surveyed powder production stages. Results indicated the environmental impact of titanium alloy powder is slightly higher than that of nickel alloy powder and their lifecycle carbon emissions are around 20 kg CO2 equivalency. The proposed Bayesian stochastic Kriging model showed more accurate predictions of energy consumption compared with conventional Kriging and stochastic Kriging models. This study enables data imputation of energy consumption during gas atomization given the physical properties and producing technique of powder materials.

Estimating metal mass flowrate in gas-atomization for metal powder production

The gas-to-metal ratio (GMR) is considered an important parameter in the gas-atomization process for producing metal powders. Consequently, correlations for estimating the mass median particle size (d50) of powders use GMR as the main parameter. In an industrial setup, it is not easy to measure the melt flowrate to ascertain the GMR. Hence, in this study, we develop a theoretical approach to estimate the melt flowrate and measure it in a pilot setup. Both our theoretical and computational fluid dynamics approaches are in good agreement with the measurements. We then conduct a parametric study to elaborate the effect of certain parameters on the melt flowrate. We believe that the theoretical approach presented here will help to quickly estimate the powder size (d50) expected from a gas-atomization system. This will help to correctly choose geometric and operating parameters to reduce the spread in powder size distribution in an actual application.

Microstructural Characteristics of Modified ODS Ni-Based Superalloys Fabricated using Laser-Powder Bed Fusion

Oxide dispersion-strengthened (ODS) superalloys are usually manufactured by a hot isostatic pressing after mechanical alloying (MA-HIP). However, this process cannot produce complex-shaped parts. Here, we used an additive manufacturing product (powders produced by laser powder bed fusion, L-PBF) to address this issue. Modified ODS Ni-based superalloy powders with a similar composition to the mechanical alloy 6000 (MA6000) were manufactured using a gas atomization process. The obtained powders and L-PBF synthesized samples were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), LPSA, and EBSD analyses.

Numerical Analysis on Gas Pore in Metal Droplet During Gas-Atomization Process

Numerical Analysis on Gas Pore in Metal Droplet During Gas-Atomization Process

CFD modelling of Close-Coupled Gas Atomisation (CCGA) process by employing the Euler-Lagrange approach to understand melt flow instabilities

This paper presents a CFD analysis of the melt and flow-field instabilities in a close-coupled gas atomisation process (CCGA) caused by the gas–melt interactions. The melt mass flow is coupled to the atomiser internal pressure, which varies over time due to the unsteady flow field. A two-phase flow of Argon gas and melt particles is modelled using a coupled Euler-Lagrange framework. Three different initial gas-to-melt ratios (GMRs) of 5.5, 2.6 and 1.32 are considered to study the gas–melt interaction. The results show that in the case GMR = 1.32, sustained instability both in the melt and in the flow-field are distinctly observed, resembling physical atomisation process. This melt fluctuation corresponded to an alternating flow-field fluctuation; alternating between open- to closed-wake condition, where the local maxima of the melt corresponded to an open-wake condition, and the local minima of the melt corresponded to a closed-wake condition.

Precise control of atomization initial stage to address nozzle clogging issue in the vacuum induction-melting gas atomization process

Vacuum induction-melting gas atomization (VIGA) is considered a widely applied method to prepare metal powders. However, the nozzle clogging problem in the VIGA process seriously affects the continuity of production and greatly increases the economic and time costs. In the atomization initial stage, the existence of unsteady state atomization mainly results in the nozzle clogging challenge. To understand the formation mechanism of nozzle clogging, a computational fluid dynamics (CFD) model was established to simulate the influence of unsteady state atomization sequence on the primary atomization of alloy melt. Typically, there are two kinds of sequence including starting the gas before pooling the alloy (namely, GA) and pouring the alloy before opening the gas (AG). The movement trajectory of the alloy melt droplet at the end of the delivery-tube was clarified. Based on CFD simulation, the atomization sequence of AG and GA was precisely controlled in the atomization pressure range of 2.5 MPa, 3.5 MPa, and 4.5 MPa to address the nozzle clogging issue. In the GA process, relatively finer powder was obtained at 3.5 MPa without nozzle clogging occurring. In contrast, the AG process greatly reduces the probability of nozzle clogging at 2.5–4.5 MPa, the final prepared powder is coarser. The predicted results of industrial experiments and numerical simulations are consistent. This study provides theoretical support for understanding the formation mechanism of nozzle clogging during the VIGA process.

Primary and secondary breakup of molten Ti64 in an EIGA atomizer for metal powder production

Electrode Induction melting Gas Atomization (EIGA) is a free-fall gas atomization process used to produce metal powders, where a swirling supersonic gas jet hits a molten metal stream atomizing it into droplets through various fragmentation mechanisms. Fragmentation mechanisms of molten Ti64 are investigated by high-speed video visualization. The role of gas pressure and melting chamber overpressure on the fragmentation mechanisms and on the particle size distribution is determined. The mechanisms observed are fiber breakup, bag breakup and Rayleigh breakup for primary fragmentation and bag breakup and shear breakup for secondary fragmentation. Increasing the gas pressure promotes shear breakup and creates finer droplets. A model based on log-stable law is proposed to fit the mass distribution according to the dominant fragmentation regime. A good agreement is observed between the different analysis (dominant atomization regime, mass cumulative distribution evolution, parameters of log-stable law). A criterion for prediction of nozzle clogging is devised.

In situ synthesis of titanium alloy powders reinforced with nanoparticles for powder bed fusion: A step towards safer and more sustainable manufacturing

Additive manufacturing technologies for metallic materials based on powder bed fusion, either with electron (PBF-EB/M) or laser beam (PBF-LB/M) have enormous industrial potential. It is known that the reinforcement of nanoparticles in the metallic matrix improves the mechanical properties. This study presents a novel method for manufacturing reinforced powder particles for PBF technology. The method involves dispersing and dissolving reinforcing nanoparticles in the metallic matrix, resulting in a composite material. The method was applied to a Ti‐6Al‐4V matrix with SiC nanoparticles as reinforcement to develop a new Titanium Matrix Composite (TMC). A route for atomizing the composite material has been developed to scale up the process on an industrial level. The atomized material has been designed to be used as feedstock with PBF-EB/M and PBF-LB/M. The feedstock is a composite powder obtained by the Electrode Inert Gas Atomization (EIGA) process after mixing and dispersing SiC nanoparticles in the Ti‐6Al‐4V matrix and consolidating the mixture into an ingot bar using Hot Isostatic Pressing (HIP). The powder bed fusion process parameters have been studied to obtain specimens with a density greater than 99.9%, and close to 100% after HIP process. The conditions for some heat treatments, such as HIP and stress relief, have been determined. The conditions of machining processes, such as milling and turning, have been studied. The material’s properties, such as chemical composition, microstructure, mechanical strength, and fatigue behavior have been evaluated. Compared to Ti‐6Al‐4V according to the ASTM F2924 standard, both the ultimate tensile strength and yield strength have been improved by 28%, and the elongation at break by between 30% and 60%. Regarding fatigue behavior, an increase of around 30–50% (high-low cycles) has been observed.

A numerical modeling framework for predicting the effects of operational parameters on particle size distribution in the gas atomization process for Nickel-Silicon alloys

Gas atomization is utilized to produce good-quality metal powders. A numerical modeling framework is developed to simulate the gas atomization process. A two-phase VOF flow model in OpenFOAM is applied to track the primary breakup of the melt stream by a high-speed gas flow. The generation of primary melt droplets is extracted from the VOF field. A Lagrangian-Eulerian multiphase flow model in Ansys Fluent is adopted to track the secondary breakup of the primary melt droplets under the high-speed gas flow. The final particle size distribution is obtained by analyzing the particles sampled at the outlet of the atomization chamber. The process of gas atomization can be affected by many factors such as the atomization equipment, operating parameters, and material properties. Sensitivity analysis is conducted through modeling to investigate the effects of these factors on particle size distribution. The model predictions are validated by specially designed gas-atomization experiments.

Selective Laser Melting and Mechanical Characterization of Superalloys Made from Recycled Parts

Geometrically complex functional parts from recycled Inconel 718 were additively manufactured and characterized. Scrap parts were melted, recycled, and used in a new gas atomization process to produce the feedstock for a selective laser melting printer. Optimal print parameters were determined using finite element simulations. Standard test methods were employed to experimentally examine the properties of parts, including their density, anisotropic tensile behavior, chemical composition, and fracture surface. The results indicated that scrap Inconel 718 parts can be used to additively manufacture high-quality functional parts. As a case-study, an automotive turbocharger was resigned and additively manufactured based on the findings of the characterization tests.

Sintering property of micro/nano core-shell molybdenum powder synthesized by mechanochemical process

In this study, a micro/nano core-shell molybdenum powder was synthesized by mechanochemical process to improve its microstructural uniformity and density by pressureless sintering the core-shell powder. The micro-sized spherical Mo powder, prepared through an electrode induction melting inert gas atomization process, was mixed with MoO3 powder and ball-milled using a three-dimensional shaker mixer. A mechanochemical process involving hydrogen reduction was employed to prepare the core-shell Mo powder. The prepared powders were sintered through the compacting and pressureless sintering. The density was measured using a densitometer to analyze the properties of sintered specimens. Phase analysis was performed using X-ray diffraction. In addition, microstructure analysis was conducted using scanning electron microscopy and electron backscatter diffraction. Comparing the sintered core-shell powder to the sintered conventional mixing powder under the same conditions, we observed that the former exhibited a uniform microstructure and higher density. Furthermore, we experimentally demonstrated the dependence of sintering properties on mixing ratio.

3D numerical modeling of gas atomization process for powder preparation based on similarity theory

Gas atomization is a widely used method to produce metal powders. However, the powders often have a wide range of particle sizes, which is not ideal for additive manufacturing. To visualize the liquid breakup during gas atomization, we have developed a novel approach that combines similarity theory with Navier-Stokes equations. The simulation utilizes the volume of fluid to discrete phase model, which captures both primary and secondary breakups. By analyzing the morphology of the lumps and particles produced by a closed-coupled atomizer, the results have shown that approximately 30% of the lumps formed turn into fibers, and 68% secondary breakup mode is vibration breakup. Based on these simulations, we propose optimized methods for modifying the liquid outlet and adjusting the gas inlet eccentricity. Overall, our approach provides a new way to directly simulate the entire gas atomization process and offers valuable guidance for gas atomization technology.

Microstructural and mechanical characterization of additively manufactured parts of maraging 18Ni300M steel with water and gas atomized powders feedstock

The demand for manufacturing components with complex geometries, good mechanical properties, and material efficiency has surged across various industries, encompassing aerospace, military, nuclear, and naval sectors. Laser powder bed fusion (LPBF), as an additive manufacturing (AM) process, has emerged as a promising method for producing ultra-high mechanical strength alloys, like maraging 300 steel (18Ni300M). However, in numerous studies in the literature concerning the effects of processing parameters on the properties of 18Ni300M steel parts fabricated through LPBF, limited attention has been given to the influence that powder atomization methods may exert on the final properties of these parts. This article investigated the effect of gas atomization (GA) and water atomization (WA) processes on the microstructure of 18Ni300M steel powders and the mechanical properties, microstructure, and chemical composition of LPBF-produced parts. The results revealed significant distinctions in the morphology, aggregation degree, and particle size distribution between the GA and WA powders, which directly influenced the microstructure and affected the amount of defects in LPBF-produced parts. Despite the similar mechanical response found in the WA and GA specimens in the elastic region, the samples produced with the WA batch presented a brittle behavior with a ductility of only 4.06%, whereas the GA parts had an elastoplastic behavior with an elongation of 11.52%. The bulks from the WA batch produced in the LPBF process were compromised due to powder contamination with oxygen, which increased gas porosity and effected fragile oxide particles visible on the fracture surface.

Ti-5Fe spherical powder alloy prepared by electrode induction gas atomization processes (EIGA) for additive manufacturing of biomedical implants

This study demonstrated the viability of the electrode induction gas atomization process (EIGA) to produce spherical Ti-5Fe powder suitable for additive manufacturing. The resulting powder is spherical and presents no surface defects. Additionally, the iron distribution throughout the microstructure is homogenous and indicates similar particle size distribution and oxygen pick-up as the conventional Ti-6Al-4V titanium alloy, thus demonstrating that the Ti-5Fe can achieve equal atomization behavior and powder outcome. The results of the study show how EIGA-type gas atomization can be an efficient scale-up route to produce Ti-5Fe low-cost titanium alloy powder for additive manufacturing, which offers a broader perspective into biomaterial application.

The Influence of Powder Particle Size Distributions on Mechanical Properties of Alloy 718 by Laser Powder Bed Fusion

Currently, metallic powders for laser powder bed fusion (LPBF) primarily come in two commercially available powder size distributions (PSDs): 15+/45− for non-reactive powders and 15+/63− for reactive powders. These powders are generally produced via gas atomization processes that create highly spherical particles with a Gaussian PSD. Because of the standard deviation within a Gaussian distribution, only small portions of the total product are used for LPBF applications. This screening process makes the other particle sizes a waste product and, thus, increases processing costs. The non-reactive 718 powder was printed with both the typical PSD of 15+/45− and a wider bimodal experimental PSD. Compared to conventional 718, the 718 alloys with bimodal PSD shows less than a 0.2% difference in density, and insignificant change in mechanical behavior. Electron backscattered diffraction studies revealed that grain sizes and morphology were similar between the two sample sets, but bimodal 718 alloy has a slightly greater degree of large grains. The study suggests that particles with wide or bimodal size distributions show promise in producing equivalent high-quality products without sacrificing mechanical properties.

Numerical analysis of droplet breakup, cooling, and solidification during gas atomisation

ABSTRACT As gas atomisation has been the main method for producing high-performance spherical powders in the past decades, its application in the production of metallic powders has become one of the main research subjects in this field. Since it is challenging to directly observe the atomising gas and to investigate melt flow states by experiments, numerical simulation is attracting increasing interest in studying the gas atomisation process. In this work, various computational fluid dynamics models were implemented to simulate the gas atomisation process. With the models, the droplet breakup, cooling, and solidification within the coupled process were investigated. The final mean particle size was predicted through numerical simulations and compared with the statistics extracted from the gas atomisation process, which shows that a reasonable mass median diameter of the particle can be predicted numerically. The results also show a clear relationship between the breakup trajectory and the resulting particle size.

Improvement in the PBF-LB/M processing of the Al-Si-Cu-Mg composition through the use of pre-alloyed powder

Among the many additive manufacturing technologies for metals, Powder Bed Fusion-Laser Beam (PBF-LB\\M) stands out for its capacity to produce complex-shaped functional parts. However, the PBF-LB\\M materials portfolio is still limited and the research into new high-performance Al-based alloys is ongoing. The improved properties with the addition of 4 wt% Cu to the AlSi10Mg alloy have been previously investigated in the literature through the in situ alloying approach in which the starting powders of Cu and AlSi10Mg are mechanically mixed and directly processed. However, inhomogeneities of alloying elements were found in samples produced with mixed AlSi10Mg+4Cu powders. To overcome this detrimental problem, the use of pre-alloyed AlSI10Cu4Mg powder obtained via gas atomisation process could be a powerful solution. With the aim of demonstrating the beneficial effects of pre-alloyed AlSi10Cu4Mg powders in laser-powder interaction, preliminary SEM investigations were conducted on cross-sectioned SSTs and bulk samples after optimising the process parameters. The deeper microstructural investigations conducted on pre-alloyed AlSi10Cu4Mg samples revealed a higher homogeneity of alloying elements, a smaller cell size of the Al-Si-Cu network (0.5 versus 0.8 μm) and a slightly smaller mean diameter of equiaxial grains compared to the mixed AlSi10Mg+4Cu ones (6.01 versus 7.34 μm). In addition, looking closer at the supersaturation level and the precipitation behaviour in pre-alloyed AlSi10Cu4Mg composition, a high solid solution level, a massive presence of Al2Cu in the cell network and only a few finely dispersed Al2Cu precipitates within the cells were found. Exploring the benefits of these microstructural features on mechanical properties, an increase in performance of about 18% in micro-hardness tests and more than 10% in tensile and compressive tests were found in the AlSi10Cu4Mg system with respect to the mixed AlSi10Mg+4Cu system. All the thorough investigations proved how using pre-alloyed powders is an important advantage in the PBF-LB/M production of complex Al-based systems.

Effect of Electrode Induction Melting Gas Atomization Process on Fine Powder Yields: Continuous Metal Melt Flow

Effect of Electrode Induction Melting Gas Atomization Process on Fine Powder Yields: Continuous Metal Melt Flow

Effect of Electrode Induction Melting Gas Atomization on Powder Quality: Satellite Formation Mechanism and Pressure

Electrode induction melting gas atomization (EIGA) is a wildly applied method for preparing ultra-clean and spherical metal powders, which is a completely crucible-free melting and atomization process. Based on several experiments, we found that although the sphericity of metal powders prepared by EIGA was higher than that of other atomization methods, there were still some satellite powders. To understand the formation mechanism of the satellite, a computational fluid dynamics (CFD) approach FLUENT and a discrete particle model (DPM) were developed to simulate the gas atomization process, and several EIGA experiments with different argon pressures (2.5-4.0 MPa) were designed. A numerical simulation of the gas-flow field verified the formation trajectory of satellites, and the Hall flow rate of the powder produced under different pressures was 13.3, 13.8, 15.6, and 16.8, which were consistent with the prediction of the numerical simulation. This study provides theoretical support for understanding the satellite formation mechanism and improving powder sphericity in the EIGA process.

Nozzle clogging in vacuum induction melting gas atomisation: influence of gas pressure and melt orifice diameter coupling

ABSTRACT The clogging problem of close-coupled nozzles in the vacuum induction melting gas atomisation (VIGA) process is studied by numerical simulation and industrial experiments. To understand the factors affecting lick back on the nozzle, volume of fluid (VOF) multiphase flow model simulation was adopted to visualise the motion of alloy melt around the outer wall of the delivery tube in the primary atomisation process. When the melt orifice diameter is 4 mm and the atomisation pressure is close to 3.5 MPa, the atomisation process is continuous, the powder particle size is fine, and the atomiser can be reused. When the orifice diameter is 5 mm, and the atomisation pressure is greater than 2.5 MPa, the risk of nozzle clogging is avoided, the powder size is relatively coarse. In the case of using the same atomiser structure, this study explains the mechanism of lick-back and the resulting nozzle damage in VIGA units.