Close-coupled Gas Atomization Research Articles

Manufacturing and aging behavior of CuCr1Zr powder: Analysis and modelling of close-coupled gas atomization of CuCr1Zr and its impact on the melt beam disintegration and analysis powder oxidation kinetics

Powder bed-based additive manufacturing methods represent an increasingly vital role in industrial applications. Specifically, there has been considerable focus on highly reflective metals, such as CuCr1Zr, in recent years. However, current research primarily revolves around developing appropriate manufacturing parameters e.g. laser powder bed fusion (PBF/LB-M) and assessing the corresponding mechanical and electrical properties of CuCr1Zr. The impact of manufacturing routines and oxidation behavior of CuCr1Zr powder are seldom discussed in additive manufacturing. Therefore, the present study addresses the analysis of powder production and the oxidation behavior of CuCr1Zr powder via close-coupled gas atomization to analyze the disintegration of a CuCr1Zr melting jet during gas atomization of CuCr1Zr by using a high-speed camera. Critical conditions for secondary disintegration were calculated as a function of the initial gas pressure. Additionally, calorimetric measurements and isothermal oxidation experiments were conducted to quantify oxide formation and growth. According to the results, initial oxide formation occurs after 42 days with CuCr1Zr powder at room temperature in a nitrogen atmosphere. Subsequently, oxide growth follows a logarithmic law, associated with the formation and conversion of Cu2O to CuO.

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.

Gas atomization of AA2017 aluminum alloy: Effect of process parameters in the physical properties of powders for additive manufacturing

Close-coupled gas atomization (CCGA) uses pressurized gas jets to atomize molten metals, producing powders suitable for additive manufacturing (AM). Optimization of processing parameters is crucial to achieve powders with good fluidity and high apparent density for laser powder bed fusion (L-PBF) and increase production yield. This study evaluated the influence of melt feed nozzle diameter, superheating temperature, and atomization pressure on AA2017 aluminum alloy powders' physical properties. Parameters variation poorly affected the median particle diameter (d50), while significantly altering the particle size distribution curves width (IDR = d90-d10). Suitable powders for AM/L-PBF were produced using a specific set of parameters (d0= 1.5 mm; ΔT= 150 °C; PG= 20 Bar), presenting appropriate fluidity and apparent density due to an optimal granulometric distribution and morphological characteristics. Mathematical analysis showed a good correlation between experimental and calculated mean particle size, suggesting an equation to predict percentile d90 based on previous correlations.

Gas atomization of fully-amorphous Ni62Nb38 powder

In this study, close-coupled gas atomization is explored to produce the binary metallic glass-former Ni62Nb38. The alloy is noteworthy due to its yield strength exceeding 3GPa, glass transition above 900 K, and considerable ductility when quenched from the melt. Ni62Nb38 is the best glass former in the Ni-Nb system, possessing an extraordinarily high glass-forming ability for a binary alloy. Yet, its critical casting thickness remains below 2 mm. Hence, Ni62Nb38 becomes a potential candidate for additive manufacturing to overcome size constraints for engineering applications. Our results reveal that spherical, fully amorphous powder with a high yield in the 20–63 µm size fraction and an oxygen level below 900wppm can be successfully produced by close-coupled gas atomization. This paves the way for using binary Ni-Nb alloy powders in additive manufacturing of large, intricate parts with very high strength.

Design and Characterization of Innovative Gas-Atomized Al-Si-Cu-Mg Alloys for Additive Manufacturing

Metallic powders are widely utilized as feedstock materials in metal additive manufacturing (MAM). However, only a limited number of alloys can currently be processed using these technologies, with most of them being casting alloys. The objective of this study is to investigate novel aluminum alloys produced via a close-coupled gas atomizer (CCGA) by adding an increasing amount of copper (4, 8, and 20 wt%) to an AlSi10Mg alloy. The obtained powders were fully characterized to evaluate the effect of copper, a well-established strengthener for aluminum alloys, in order to correlate the obtained hardness to the powder phase composition and microstructure. In particular, a dendritic microstructure was observed in all alloys, and, as the copper content was increased, the size of the secondary dendrite arm spacing (SDAS) decreased progressively. Consequently, the hardness measured on the powder cross-section linearly increased with the copper content, and the hardness value of 185 ± 13 HV of the AlCu20Si10Mg composition was found to be twice that of the AlSi10Mg alloy (88 ± 5 HV).

Investigation on close-coupled gas atomization for Fe-based amorphous powder production via simulation and industrial trials: Part I. Melt breakup behaviors during primary atomization

The primary atomization process is simulated by Volume of Fluid (VOF) model and dynamic adaptive mesh method. The influence of melt mass flow rate and atomization pressure on the breakup process is investigated, and the effect of hot gas atomization is also evaluated. The results show that the breakup is insufficient when the melt mass flow rate is larger than 0.075 kg s−1, while the liquid film breakup inducing the nozzle clogging occurs when the melt mass flow rate is too low (0.025 kg s−1). The backflow of droplets occurs at low atomization pressure (1.0 MPa), and various defects (satellite powders, hollow powders and needle-shaped powders) appear when the atomization pressure is larger than 3.0 MPa. Although the breakup efficiency can be significantly improved by increasing the gas temperature, severe deformation of the gas-liquid interface is induced due to the Kelvin–Helmholtz wave and gas-liquid interaction, easily leading to the formation of hollow powders. Besides, the gas-to-melt ratio (GMR) is identified as a simple criterion for predicting primary atomization breakup modes, with liquid film breakup occurring when GMR≥4.4 and "fountain" breakup occurring when GMR≤4.3. In this work, not only the gas-liquid interaction is systematically analyzed by establishing a flow-heat transfer-VOF coupling model, but also the GMR is proposed to predict the breakup mode in the industrial production, which can provide theoretical and methodological guidance for the optimization of atomization operational parameters.

Experimental investigation of a supersonic close-coupled atomizer employing the phase Doppler measurement technique

Along with the growing economic importance of metal additive manufacturing by means of laser powder bed fusion, the demand for high-quality metal powders as the corresponding raw material is also increasing. However, the physics involved in supersonic close-coupled gas atomization, which is often employed for the production of these powders, are not well understood and extensive experimental data is scarce, leading to a lack of reliable predictive modeling capabilities. In this experimental study, local particle size and velocity distributions for the spray produced by a generic supersonic close-coupled atomizer are obtained using the phase Doppler measurement technique. The gas stagnation pressure and the liquid mass flow rate are varied systematically and independently. Three working liquids are considered, investigating the influence of the liquid dynamic viscosity on the atomization result. The particle size is shown to be sensitive to changes in both the gas stagnation pressure and the liquid mass flow rate. Notably, it is not an unambiguous function of the gas-to-liquid ratio. Furthermore, the effect of the liquid dynamic viscosity appears to be negligible. In conclusion, these are important insights for formulating physics-based models for the supersonic close-coupled atomization process.

Investigation on close-coupled gas atomization for Fe-based amorphous powder production via simulation and industrial trials: Part II. Particle flight and cooling during secondary atomization

A two-way coupling Discrete Phase Model (DPM) is applied to calculate the secondary atomization process. The particle flight and cooling processes are studied under different process parameters. The results show that the average particle size (d50) depends on the gas-liquid interaction and decreases with increasing gas-to-melt ratio (GMR). The standard deviation of the particle size (d84/d50) increases as the melt mass flow rate increases, and both high and low atomization pressures result in a high d84/d50. The average cooling rate of particles can be improved by reducing the melt mass flow rate and increasing the atomization pressure. By increasing the gas temperature to 400 K, the d50 can be significantly reduced and the average cooling rate can be approximately increased two times, indicating that the hot gas atomization technique can effectively improve the yield of fine amorphous powders. However, excessive gas temperature not only has a limited effect on improving the cooling rate, but also significantly increases the d84/d50 and defective particles, suggesting that the gas temperature must be matched to the atomization process to achieve ideal effects. The powders produced at 2.0 MPa and 0.075 kg·s−1 exhibit good circularity with a d50 of 58.9 μm, which is in good agreement with the simulation analysis. Moreover, the powders with sizes less than 50 μm exhibit high amorphous fraction (96.6%) and outstanding soft magnetic properties. In this work, a flow-heat transfer-DPM coupling model is established to provide theoretical guidance for the production of high-performance Fe-based amorphous powders.

Additive manufacturing of Inconel-625: from powder production to bulk samples printing

PurposeFor metal additive manufacturing, metallic powders are usually produced by vacuum induction gas atomization (VIGA) through the breakup of liquid metal into tiny droplets by gas jets. VIGA is considered a cost-effective technique to prepare feedstock. In VIGA, the quality and the morphology of the produced particles are mainly controlled by the gas pressure used during powder production, keeping the setup configuration constant.Design/methodology/approachIn VIGA process for metallic additive manufacturing feedstock preparation, the quality and morphology of the powder particles are mainly controlled by the gas pressure used during powder production.FindingsIn this study, Inconel-625 feedstock was produced using a supersonic nozzle in a close-coupled gas atomization apparatus. Powder size distribution (PSD) was studied by varying the gas pressure.Originality/valueThe nonmonotonic but deterministic relationships were observed between gas pressure and PSD. It was found that the maximum 15–45 µm percentage PSD, equivalent to 84%, was achieved at 29 bar Argon gas pressure, which is suitable for the LPBF process. Following on, the produced powder particles were used to print tensile test specimens via LPBF along XY- and ZX-orientations by using laser power = 475 W, laser scanning speed = 800 mm/s, powder layer thickness = 50 µm and hatch distance = 100 µm. The yield and tensile strengths were 9.45% and 13% higher than the ZX direction, while the samples printed in ZX direction resulted in 26.79% more elongation compared to XY-orientation.

Gas atomization of A2 tool steel: Effect of process parameters on powders' physical properties

In this study, powders of the A2 tool steel were produced by close-coupled gas atomization using argon gas aiming their use in additive manufacturing (AM) technologies. The effects of melt overheating and gas atomization pressure on their physical properties were analyzed. The powders were separated into different particle size ranges, and a complete morphological characterization was carried out. The effect of back pressure was verified due to a substantial increase in the gas-to-melt mass flow rates ratio (GMR) with increasing gas pressure. Atomization gas pressure showed a slightly more significant influence on particle size distribution; however, the melt overheating effect was also significant. As the GMR increases, the median particle size decreases to a certain threshold. Above this, particle size cannot be considerably reduced with increasing GMR.

Effect of gas Mach number on the flow field of close-coupled gas atomization, particle size and cooling rate of as-atomized powder: Simulation and experiment

Gas velocity is a key parameter regulating the particle size and the cooling rate of the gas atomized powder applied in additive manufacturing, metal injection molding, thermal spraying, and soft magnetic composites. In this paper, on basis of the well-designed close-coupled nozzles with different gas Mach numbers at the outlet, the gas field structure was simulated by Computational Fluid Dynamics (CFD) software, and the process of cooling and solidification of Fe-6.5 wt% Si metal droplets was calculated by finite difference method. The results show that with the increase of Mach number, both the gas velocity downstream and the pressure at the base of melt delivery tube tip rise, whereas the mass flow rate of the melt decreases. The nozzles with high Mach number can produce finer powder with higher cooling rate. The median diameter of the powder prepared by the nozzle with Mach numbers of 1.0, 1.5, 2.0, and 2.5 is 44.9, 39.0, 32.5, and 29.1 μm, respectively, and the corresponding cooling rate of the metal droplet with a diameter of 80 μm is 2.85 × 104, 2.98 × 104, 3.32 × 104, and 3.50 × 104 K/s, respectively. This work provides new ideas and suggestions for the preparation of metal powder with small particle size at high cooling rate.

Breakup process modeling and production of FeSiAl magnetic powders by close-coupled gas atomization

Close-coupled gas atomization is extensively used in the industrial production of alloy powders due to the advantages of high efficiency, low cost and excellent powder properties. In order to investigate the complex gas-liquid interaction during atomization, primary atomization was simulated through the VOF (Volume of Fluid) model and the dynamic adaptive mesh method, and a two-way coupling DPM (Discrete Particle Model) was used to simulate secondary atomization. The results showed that under the low melt mass flow rate of 0.0050 kg s−1, the flow separation and droplet backflow occurred at the atomization pressure of 1 MPa, while gas-liquid interfaces deformed and rotated drastically when the atomization pressure is above 3 MPa, which led to the formation of hollow powders. When the melt mass flow rate was 0.0150 kg s−1, the d50 decreased from 40.7 to 38.4 μm as the atomization pressure increased from 2 to 3 MPa. However, the chance of collision between particles increased due to the decrease in the spray cone angle, and both the standard deviation of particle size and atomization efficiency deteriorated, which indicated that 2 MPa was the optimum atomization pressure. As the mass flow rate increased from 0.0050 to 0.0150 kg s−1, the gas to melt ratio decreased, but the d50 only increased from 32.3 to 40.7 μm, indicating that the mass flow rate of 0.0150 kg s−1 did not significantly affect the particle size distribution, but also contributed to improve the production efficiency and avoided the risk of the nozzle freeze-off. The d50 of the spherical FeSiAl powders produced by the industrial tests at 2 MPa and 0.0150 kg s−1 was 44.7 ± 2.1 μm, which was basically consistent with the simulation results, indicating that the parameter optimization by the coupling model developed in this study could provide theoretical and practical guidance for the preparation of high-performance alloy powders by gas atomization.

Generation of Hydrogen through the Hydrolysis of Gas Atomized High Purity Mg Powder

Generating hydrogen through hydrolysis of metal magnesium with water is a very promising strategy for portable applications because it is clean, has high energy density and operability. In the present study, high purity ultrafine Mg powder was prepared using close-coupled gas atomization. Thereafter, the microstructure of the powder was investigated through X-ray diffraction and scanning electron microscopy. The results showed that increasing the speed of ball milling improved the reaction activity of Mg powder. Moreover, a higher water temperature was shown to be beneficial in improving hydrolysis. Moderate amounts of alcohol in water could also improve the yield of hydrogen.

Withdrawn: Research progresses in flow field of close-coupled atomizer and atomization mechanism

With the development of part manufacturing technology, many fields, such as medical treatment, military industry, machine and three-dimensional (3D) printing, propose increasingly higher requirements on performances of metal/alloy powder. Low oxygen content, accurate alloy composition, small particle size and high particle sphericity become characteristics of high-quality powder. With high atomization efficiency, low oxygen content in powder and high cooling rate, the close-coupled gas atomized powder preparation technology is an ideal choice to prepare high-quality powder. Nevertheless, powder preparation technology based on close-coupled gas atomization is a complicated process with mutual coupling effects of multiple-phases flows. However, the atomization mechanism still is not revealed fully yet. Close-coupled gas atomized powder preparation technology is facing with great challenges in mass preparation of high-quality powders at a low cost. It is expected to improve close-coupled gas atomized powder preparation technology and even achieve breakthroughs in atomizing principle. For this reason, this study summarized atomizer structure, gas atomization flow field test technology and gas flow field numerical simulation thoroughly according to existing associate studies. Moreover, the gas atomization mechanism of close-coupled atomizer was analyzed. Finally, further deep studies on atomizing characteristics and atomization mechanism of close-coupled vortical loop slit atomizer were prospected and several research directions were proposed. This paper summarized atomizer structure, gas atomization flow field test technology and gas flow field numerical simulation. Moreover, the gas atomization mechanism of close-coupled atomizer was analyzed. Further deep studies on atomizing characteristics and atomization mechanism of close-coupled vortical loop slit atomizer were prospected and several research directions were proposed.

Simulation and validation of the gas flow in close-coupled gas atomisation process: Influence of the inlet gas pressure and the throat width of the supersonic gas nozzle

The effectiveness of a close-coupled gas atomisation process largely depends on the operational and the geometric variables. In this study, Computational Fluid Dynamics (CFD) techniques are used to model and simulate the gas flow in the melt nozzle area for a convergent-divergent, close-coupled gas atomiser in the absence of the melt stream. Firstly, a reference case, in which the atomisation gas is nitrogen at 50 bar and a supersonic gas nozzle with a throat width of L0 has been modelled, is presented. Then, the influence of both the inlet gas pressure and this design parameter are investigated, comparing the numerical results provided by simulations varying the inlet pressure from 5 to 80 bar and modelling different convergent-divergent gas nozzles with throat widths of 0.29∙Lo, 0.5∙Lo, 0.77∙Lo and 2∙Lo respectively. The simulation results show how similarly these two parameters modify gas mass flow rates, gas velocity fields, aspiration pressures in the melt delivery tube or the size of the recirculation zones below the melt nozzle. Therefore, it can be stated that this geometric variable of the gas nozzle may be as relevant as the inlet pressure in the atomisation process. The most important novelty of this study is related to experimental validation of the numerical results using the Particle Image Velocimetry (PIV) technique and through direct measurements of gas mass flow rates, with a clear correlation between simulated and measured data. Moreover, some results obtained with experimental atomisations using copper and nitrogen are also presented. The experimental results show that finer powders are produced by increasing the atomising pressure or the throat width of the supersonic gas nozzle, which can be directly related to the gas flow dynamics calculated numerically.

Multiphase model to predict particle size distributions in close-coupled gas atomization

A novel two-stage multiphase model is developed for close-coupled gas atomization by combining formulations available in the literature. Primary atomization is simulated using an Eulerian atomization model, and the outputs are used as inputs of a Lagrangian particle tracking approach to predict the particle size distribution resulting from secondary atomization. The results given by the primary atomization model are validated with published Direct Numerical Simulations (DNS) values and by comparison with experimental images of the spray, while the particle size distributions obtained are accurately fitted to a log-normal distribution, and with powder mean diameters showing good agreement with experimental data. The variation of powder characteristic diameters d10, d50, and d90 as a function of the gas-to-melt mass flow rate ratio follows correct trends, and the values of powder mean diameters d50 are correctly predicted by the model.

Effects of Gas Mach Number on the Flow Field of Close-Coupled Gas Atomization, Particle Size and Cooling Rate of As-Atomized Powder: Simulation and Experiment

Effects of Gas Mach Number on the Flow Field of Close-Coupled Gas Atomization, Particle Size and Cooling Rate of As-Atomized Powder: Simulation and Experiment

Evaluation of a Mathematical Model Based on Lubanska Equation to Predict Particle Size for Close-Coupled Gas Atomization of 316L Stainless Steel

Close-Coupled Gas Atomization (CCGA) is often used to produce spherical metal powders with a wider Particle Size Distribution (PSD) (10 – 500 µm) compared to that required by the main Additive Manufacturing processes (10 – 105 µm). This work presents an accuracy evaluation of a mathematical model based on the Lubanska equation to predict the d50 for CCGA. Atomization experiments of 316L steel were conducted to evaluate the tip diameter and atomization gas pressure effects on PSD and, the d50 experimental results were used as the reference to the mathematical model evaluation. The mathematical model accuracy could be improved by: (i) considering the backpressure phenomenon for the metal flow rate calculation, since it was an important inaccuracy source; (ii) reviewing the tip diameter effect, which had a lower impact on d50 than that predicted by the Lubanska equation. The atomization gas pressure was the most influential parameter on d50 and d90 and the increase of the gas pressure led to a significant reduction in PSD and, consequently, increased yield.

Preparation of Fe-Cr Alloy Powder by Close-Coupled Vacuum Induction Melting Gas Atomization for Laser Cladding

Preparation of Fe-Cr Alloy Powder by Close-Coupled Vacuum Induction Melting Gas Atomization for Laser Cladding

Experimental study of the influence of operational and geometric variables on the powders produced by close-coupled gas atomisation

The effect of several operational and geometric variables on the particle size distribution of powders produced by close-coupled gas atomisation is analysed from a total of 66 experiments. Powders of three pure metals (copper, tin and iron) and two alloys (bronze Cu-15 wt% Sn and stainless steel SS 316 L) have been produced. Nitrogen, argon and helium were used as atomising gases. It is shown that the gas-to-metal ratio of volume flow rates (GMRV) is more relevant than the ratio of mass flow rates (GMR) in order to analyse the effect of atomisation variables on the particle size. Kishidaka's equation, originally proposed for water atomisation, is modified to predict the median particle size in gas atomisation. The accuracy of the new equation is compared with that of Lubanska, and Rao and Mehrotra. Kishidaka's modified empirical correlation is the most accurate in predicting the median particle size of the powders produced in this work. The morphology of the produced powders is studied by scanning electron microscopy (SEM) and it is observed that the melt superheat can play an important role in the aggregation of fine particles (< 10 μm), which increases the fraction of large particles (> 100 μm).