Gas Atomization Research Articles

Investigation of Mechanical and Magnetic Properties of Co-Based Amorphous Powders Obtained by Atomization.

Properties of Co-based alloys with high Glass Forming Ability (GFA) in the form of powder are still not widely known. However, powders of high GFA alloys are often used for the development of bulk metallic glasses by additive manufacturing. In this work Co47.6B21.9Fe20.4Si5.1Nb5% at. and Co42B26.5Fe20Ta5.5Si5Cu1% at. were developed by gas-atomization. Obtained powders in size 50–80 µm were annealed at Tg and Tx of each alloy. Then SEM observation, EDS analyses, differential thermal analysis, X-ray diffraction, nanoindentation, Mössbauer, and magnetic properties research was carried out for as-atomized and annealed states. The gas atomization method proved to be an efficient method for manufacturing Co-based metallic glasses. The obtained powder particles were spherical and chemically homogeneous. Annealing resulted in an increase of mechanical properties such as hardness and the elastic module of Co47.6B21.9Fe20.4Si5.1Nb5% at and Co42B26.5Fe20Ta5.5Si5Cu1%, which was caused by crystallization. The magnetic study shows that Co47.6B21.9Fe20.4Si5.1Nb5 and Co42B26.5Fe20Ta5.5Si5Cu1 are soft magnetic and semi-hard magnetic materials, respectively.

Multi-physics coupling simulation of electrode induction melting gas atomization for advanced titanium alloys powder preparation

A numerical modeling method is proposed for the melting process of Titanium metals of Titanium alloys powder preparation used for 3D printing. The melting process simulation, which involves the tight coupling between electromagnetic field, thermal field and fluid flow as well as deformation associated during the melting process, is conducted by adopting the finite element method. A two-way coupling strategy is used to include the interactions between these fields by incorporating the material properties dependent on temperature and the coupling terms. In addition, heat radiation and phase change are also considered in this paper. The arbitrary Lagrangian–Eulerian formulation is exploited to model the deformation of Titanium metal during the melting process. The distribution of electromagnetic flux density, eddy current density, temperature, and fluid flow velocity at different time can be determined by utilizing this numerical method. In a word, the method proposed in this paper provides a general way to predict the melting process of electrode induction melting gas atomization (EIGA) dynamically, and it also could be used as a reference for the design and optimization of EIGA.

Production of magnets from the material of Fe - Cr - Co system by selective laser sintering

The article presents results of the study of possibilities of selective laser melting (SLM), or so-called additive technologies, for production of permanent magnets. This process makes it possible to produce not only product models and prototypes, but also finished functional products using layer-by-layer addition of material and binding of particles and layers to each other. An alloy based on Fe - Cr - Co system has been chosen as the material for evaluation of the compared technologies for permanent magnets production. The application fields of selective laser melting (SLM/SLP) were considered. The powders obtained by different methods are taken for the research. Classical technology of magnetic alloy casting also was analyzed. The studies of magnetic materials and comparisons of the properties of powder magnets with standard data were carried out. On the basis of 25Kh15KA alloy powder sprayed by gas atomization, permanent magnets with a material density of 7.59 - 7.55 g/cm3 can be manufactured at the SLP plant. They meet the requirements recommended by the state standard GOST 24897 - 81, and achieve characteristics of magnets made by classical metallurgical technologies. To study the magnetic and physical properties, four samples were produced with the same geometry in the shape of a cube. During production of each of the test samples, different operating modes of the plant were selected. Samples were made on the basis of the “Kurchatov Institute” NRS enterprise (the “Prometheus” Central Research Institute of Construction Materials) as part of the NIO-35 technological complex. It was established that characteristics of the powders obtained by gas atomization qualitatively exceed characteristics of the powders obtained by other methods, and the produced magnets meet all the requirements for magnets.

The influence of particle size and heat treatments on the transformation energies of a gas atomized Cu-Al-Ni-Mn shape memory alloy

Forward and reverse transformation temperatures of shape memory alloys are significantly affected by their thermal and processing history. Controlling these temperatures is of great importance when designing materials displaying shape memory effect. In this direction, the present work shows the influence of particle size and heat treatments on thermodynamic properties of a gas-atomized Cu-Al-Ni-Mn shape memory alloy. Commercially pure elements were used in the gas atomization process and differential scanning calorimetry was used to measure As, Af (austenitic start and final transformation temperatures), Ms, Mf (martensitic start and final transformation temperatures), transformation temperature hysteresis and chemical/non-chemical energies involved in the martensitic-austenitic transformation. The influence of quenched-in defects and annealing was also studied. Results show a correlation between particle size and transformation energies, which can be attributed to atomic ordering in the austenitic phase upon cooling, after the solidification process. This is further confirmed by the increase in the reverse and forward transformation temperatures after thermal cycling and annealing.

Particle morphology of water atomised iron‑carbon powders

Water atomisation can produce metal powders faster and at lower cost than gas atomisation, but it is well known that the powder particles are irregular and may contain a large number of pores. The current study analyses three iron‑carbon alloys with different superheats, produced as powder by water atomisation and compares the particle shapes and porosity in each. The alloy with the most carbon (4.2 wt%) showed the highest circularity (0.72) for 20–45 μm particles, but the lowest (0.59) for 180-212 μm particles. This is consistent with collisions between droplets affecting particle shape. The lowest-carbon melt (0.22 wt%) solidified fastest, so underwent fewest collisions and showed similar circularity for all particle sizes. The breakdown of water to form hydrogen and the formation of hydrogen bubbles was the most likely cause of porosity. The findings of this study may be used to inform future water atomisation process design to control particle shape and minimise porosity.

Interaction between high-velocity gas and liquid in gas atomization revealed by a new coupled simulation model

Due to the high efficiency and low cost, gas atomization (GA) has been widely applied to produce metal powders. In this paper, the GA process is first modeled by combining the volume of fluid (VOF) model with dynamic adaptive mesh and the discrete phase model (DPM) to simulate the formation of the powders and the evolution of the defects. Simulation results show that the Kelvin-Helmholtz instability in the primary atomization and the membranous droplet breakup and closure in secondary atomization can form the hollow powder. While the presence of the satellite powder is caused by the collisions between the large and small droplets with different velocities. Moreover, the irregular powder is produced when the drag force is not enough to separate the droplets but deforms them. The estimated morphology and size distribution of the particles have a good agreement with the experimental ones. Finally, the possible measures to reduce the defects of the powders have been put forward based on the revealed mechanism of defect evolution. This work provides a deep simulation insight into the GA process, towards producing high-quality metal powders for additive manufacturing on a large scale.

Study of toxic elements in propolis

There is a threat of heavy metals and toxic elements entering the beekeeping products in relation to the deterioration of the ecological situation. In this regard, a study of one of the most popular beekeeping products, propolis, from the territory of two regions of Russia (Ryazan Oblast and Krasnodar Krai) for the level of Pb, Cd, Sr and the toxic element As was undertaken. The studies were made from 2004 to 2019. The amount of elements was determined spectrophotometrically with an atomic absorption spectrophotometer Spectr AA 220FS. Lead, cadmium and strontium levels were determined using an air-acetylene flame on a gas atomizer. The level of arsenic was determined on a graphite oven of a spectrophotometer using a palladium modifier made by “Mersk”. The lead level in propolis was from 0 to 0.19 mg/kg that exceeds the threshold limit value by a factor of 1.2-12.3. The concentration of cadmium, strontium, arsenic in the studied propolis samples does not exceed the threshold limit value: 0-0.164 mg/kg, 2.1-21.01 mg/kg, 0-1.04 μm/kg, respectively. The accumulated experimental data indicate the need to adjust the threshold limit value (SanPiN 2.3.2. 1078-01) of lead level in propolis. The dynamics of propolis pollution with toxic elements was evaluated in the course of the research. The results of this evaluation confirmed the possibility of using propolis as a bioindicator of environmental pollution with heavy metals and toxic elements. It is necessary to monitor the propolis safety to determine its level of contamination with heavy metals and toxic elements, when using it as a source of biologically active compounds and as a raw material for Pharmacy (making extracts, tablets, ointments, syrups, suppositories, plasters).

Intensive laser repair through additive manufacturing of high-strength martensitic stainless steel powders (I) –powder preparation, laser cladding and microstructures and properties of laser-cladded metals

The intensive high-strength martensitic stainless steel (IHMSS) was designed and prepared. Influences of various parameters of electrode-induced gas atomization (EIGA) on qualities of IHMSS powders were investigated through the orthogonal test design. The IHMSS powders prepared through the optimized technology present a favorable comprehensive quality. The additive manufacturability of IHMSS powder was explored by laser cladding with coaxial powder feeding. Effects of parameters on the forming quality of IHMSS laser-cladded layers were explored. The microstructures and properties of the IHMSS deposit were characterized. Obvious macrosegregation at the interface between the base plate and the deposit and the mechanical properties deliver significant anisotropy. The sample along the Y direction (laser scanning direction) shows the highest tensile strength of 1385 MPa and elongation of 25.7%); the sample along the Z direction (vertical direction) is found to have the lowest tensile strength of 1068 MPa and elongation of 12.2%.

Flexible Powder Production for Additive Manufacturing of Refractory Metal-Based Alloys

The quality and properties of metal powders are essential for powder metallurgical (PM) processes in general and for additive manufacturing (AM) processing routes in particular. Thus, a variety of atomization technologies were established meeting the multiple needs of the different processing technologies. However, the production of refractory metal alloy powder remains challenging due to their high liquidus temperatures (>2000 °C), the formation of brittle intermetallic phases, as well as the reactivity with and sensitivity to interstitials of the constituting elements. In this contribution, powders made of Mo-20Si-52.8-Ti (at.%) were produced by a novel ultrasonic atomization (UA) process at laboratory-scale using an industrial electrode induction gas atomization (EIGA) process with a modified electrode concept for the first time. UA allows flexibility in alloy composition due to the arc melting-based principle, while the EIGA electrode is PM manufactured from elemental powders to provide similar flexibility on a larger scale. The powders resulting from these two processes were compared with respect to size distribution, sphericity, microstructure and phase constitution, chemical composition, and interstitial impurity content. In addition, several powder batches were produced with the UA process in order to assess the process reliability and stability. The properties, quality, and quantities of UA powders perfectly meet the requests for alloy development for powder bed fusion AM, while the modified EIGA process allows the upscaling of the alloy powder quantities.

The role of powder morphology in particle movement behavior in laser powder bed fusion with an emphasis on fluid drag

This study investigates the movement behavior of particles of dissimilar morphology in the powder bed in Laser Powder Bed Fusion. Gas atomized (GA) and water atomized (WA) low alloy steel powders were employed to study their motion around the laser scan path. Particle velocities, entrainment distances and denudation zones were measured for both powders using high-speed imaging. The entrainment of GA powder particles in front of the laser beam towards the process area was initiated 1.6 mm from the edge of the melt pool, whereas the distance was 0.6–0.8 mm for the WA powder. The differences in observed behavior were related to the variations in particle shape of the two types of powder. The processing of WA powder resulted in a 16% narrower denudation zone (for a low volumetric energy density) compared to GA powder. However, the denudation width difference decreased with increasing volumetric energy density, most likely due to a steeper pressure gradient in the process area which diminishes the impact of powder shape. X-ray computed microtomography was utilized to estimate the drag force acting on the powder particles of various morphologies. The results showed that the radial drag force exerted on GA powder was 64% greater than when using WA powder. Moreover, if the WA powder particles were of elongated shape the drag force decreased by almost an order of magnitude, demonstrating the importance of the particle's morphology in the process dynamics.

Methane and carbon dioxide hydrates properties in presence of Inconel 718 particles: Analyses on its potential application in gas separation processes to perform efficiency improvement

Methane and carbon dioxide hydrates were formed in a small-scale experimental apparatus and in presence of a pure-quartz porous sediment impregnated with Inconel 718 particles produced via gas atomization and destined to additive manufacturing applications. The aim of this work consisted in exploring for the first time the effect of such material, commonly used in additive manufacturing, for gas hydrates production, in order to detect its properties in this field and its potential applications. Three In concentrations were tested: 8.68, 17.36 and 26.04 wt%. Multiple tests were carried out for both the guest compounds considered. This compound was found to act as promoter for the process in presence of methane and inhibitor in presence of carbon dioxide. In particular, at temperatures ranging from 2.1° to 6.5 °C and with 26.04 wt% In, CO2 molecules required higher pressure than CH4 molecules for being trapped into water cages. Because CO2 hydrates naturally form at milder thermodynamic conditions than CH4 hydrates, the existence of a narrow thermodynamic region, with this reverse property, was highlighted for being suitably exploited to improve the efficiency of CO2/CH4 mixture separation via hydrates formation.

Коррозионностойкие стали в аддитивном производстве

This review discusses the main methods for producing spherical powder particles of corrosion-resistant steels as a material widely used in all industries. Also the examples of products made by modern additive methods are described. Currently, spherical powder particles of corrosion-resistant steels are used in the following additive methods: selective laser melting, selective laser sintering, direct laser sintering, and electron beam melting. Each of these methods has its own requirements for the characteristics of spherical powder particles of corrosion-resistant steels. The review provides a brief description of the principles of operation of each method and the requirements for spherical powder particles of corrosion-resistant steels. It also considers a detailed description of each method of additive manufacturing with a description of the principle of operation and specific examples of obtaining spherical particles of corrosion-resistant steel powders with indication of their properties (morphology, structural features, chemical composition, fluidity, bulk density). A comparative analysis was carried out with a description of disadvantages and advantages of each method. Examples of the use of spherical particles of corrosion-resistant steel powders for the manufacture of products by various additive methods (including post-processing) are given with description of the final products characteristics. Based on the data presented, a conclusion was made about the preferred methods for obtaining spherical particles of corrosion-resistant steel powders for specific additive methods used in modern industry. The review considers the following methods for producing spherical powder particles: water atomization (atomization of liquid metal with a jet of water under pressure); gas atomization (atomization of the melt with a jet of inert gas (argon or nitrogen) under pressure); centrifugal atomization (atomization of molten metal with a high-speed rotating disc); ultrasonic atomization (atomization of liquid metal by ultrasound); non-contact atomization (atomization of liquid metal with a powerful pulse of electric current); plasma wire spraying; plasma spraying of a rotating electrode; plasma spheroidization.

ВЛИЯНИЕ СПОСОБА ПОЛУЧЕНИЯ МЕТАЛЛИЧЕСКИХ ПОРОШКОВ НА МИКРОСТРУКТУРУ И ТЕКУЧЕСТЬ ГРАНУЛЯТА МАГНИТОТВЕРДОГО СПЛАВА

A comparison is made of the characteristics of metal powders of a hard magnetic alloy produced by centrifugal spraying and gas atomization. Comparative studies of particle morphology and particle size distribution of powders are presented in order to determine them.

Microstructural characterization and wear resistance of boride-reinforced steel coatings produced by Selective Laser Melting (SLM)

Surface engineering is an effective method to extend the lifespan of carbon steels submitted to severe wear degradation. In this work, the surface of a low carbon steel (AISI 1020) was protected by a boron-modified stainless steel coating produced by selective laser melting (SLM). Commercial precursors such as 2205 duplex stainless steel and ferrous-alloy (Fe-B) were used to produce boron-modified steel powders by two different routes: i) gas atomization, and ii) gas atomization followed by mechanical milling of large particles (to reduce the particles’ size and to add a solid lubricant – hexagonal boron nitride, h-BN). Thick coatings (200 – 600 μm) metallurgically bonded to the substrate were produced with reduced dilution, characterized by refined, hard and rigid borides homogeneously distributed within the predominant ferritic matrix. The boron-modified steel coatings were hard (~800 HV0.5) and wear-resistant, since the specific wear rate was ~4.5 × 10−5 mm3·N−1·m−1, much inferior to that of the soft (~120 HV0.5) AISI 1020 substrate (~1.8 × 10−3 mm3·N−1·m−1). Although recognized as solid-lubrificant, the coating produced by powder containing h-BN additions did not exhibit reduced coefficient of friction. Given the high temperatures achieved during SLM process, the h-BN may decompose, being the remaining content insufficient to enable the formation of an effective lubrificating layer. The present work contributes to widespread the use of SLM to produce wear-resistant protective coatings using boride-reinforced stainless steels.

Numerical investigation on flow process of liquid metals in melt delivery nozzle during gas atomization process for fine metal powder production

Based on volume of fluid (VoF) interface capturing method and shear-stress transport (SST) k-ω turbulence model, numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle (MDN) during gas atomization (GA) process. The experimental validation indicated that the numerical models could give a reasonable prediction on the melt flow process in the MDN. With the decrease of the MDN inner-diameter, the melt flow resistance increased for both molten aluminum and iron, especially achieving an order of 102 kPa in the case of the MDN inner-diameter ≤1 mm. Based on the conventional GA process, the positive pressure was imposed on the viscous aluminum alloy melt to overcome its flow resistance in the MDN, thus producing powders under different MDN inner-diameters. When the MDN inner-diameter was reduced from 4 to 2 mm, the yield of fine powder (<150 μm) soared from 54.7% to 94.2%. The surface quality of powders has also been improved when using a smaller inner-diameter MDN.

ВЛИЯНИЕ СПОСОБА ПОЛУЧЕНИЯ МЕТАЛЛИЧЕСКИХ ПОРОШКОВ НА МИКРОСТРУКТУРУ И ТЕКУЧЕСТЬ ГРАНУЛЯТА МАГНИТОТВЕРДОГО СПЛАВА

A comparison is made of the characteristics of metal powders of a hard magnetic alloy produced by centrifugal spraying and gas atomization. Comparative studies of particle morphology and particle size distribution of powders are presented in order to determine them.

Pre-breakup mechanism of free-fall nozzle in electrode induction melting gas atomization

Based on the preparation of TC4 powder under electrode induction melting gas atomization in this study, the concept of pre-breakup in the free-fall nozzle channel is innovatively proposed. The computational fluid dynamics method was used to simulate the pre-breakup process, and the effect of initial droplet size on the pre-breakup process was investigated. The pre-breakup process of TC4 discontinuous droplets was simulated using a Eulerian-Eulerian volume of fluid multiphase model and the Reynolds stress model. In addition, the Eulerian-Lagrangian discrete phase model and the unstable breakup model were employed to simulate the entire atomization process of the discontinuous droplets and predict the size of the powder particles. Some simulation results were verified based on experimental measurements. The results exhibit that the pre-breakup process of discontinuous droplets can be mainly divided into the formation of ellipsoidal droplets, the formation of annular disk-shaped stacked droplets, the formation of disk-shaped liquid films, and the breakage of the disk-shaped liquid film. In addition, the pre-breakup of small droplets or droplets with appropriately increased size can effectively prevent the broken droplets from hitting and adhering to the inner wall surface of the nozzle channel. Finally, with the increase of initial droplet size, the atomized powder particle size becomes gradually coarse, and the powder particle size distribution becomes gradually concentrated.

Performance Testing and Rapid Solidification Behavior of Stainless Steel Powders Prepared by Gas Atomization.

Gas atomization is a widely used method to produce the raw powder materials for additive manufacturing (AM) usage. After the metal alloy is melted to fusion, gas atomization involves two relatively independent processes: liquid breakup and droplet solidification. In this paper, the solidification behavior of powder during solidification is analyzed by testing the powder’s properties and observing microstructure of a martensitic stainless steel (FeCrNiBSiNb). The powder prepared by gas atomization has high sphericity and smooth surface, and the yield of qualified fine powder is 35%. The powder has typical rapid solidification structure. Collision between powders not only promotes nucleation, but also produces more satellite powder. The segregation of elements in powder is smaller as the result of high cooling rate which can reaches 4.2 × 105 K/s in average. Overall, the powder prepared by gas atomization is found to have good comprehensive properties, desired microstructure, and accurate chemical component, and it is suitable for various additive manufacturing techniques.

Effect of water atomization on properties of type 4130 steel processed by L-PBF

In the current investigation, a comparison between two type 4130 low-alloy steel powders produced by both gas and water atomization, and later processed by Laser-powder bed fusion was carried out. Samples fabricated from the water atomized powder showed relative density levels exceeding 99%, slightly lower than those achieved with the gas atomized powder. Both steels exhibited similar metallurgical features after solidification, showing a microstructure that is mainly composed of partially tempered martensite, bainite, and retained austenite. Additionally, micro-segregation of alloying elements was detected in the as-built microstructure, which contribute to a local increase in microhardness. The excess of oxygen found in the water atomized powder tended to combine with silicon and form nano-sized SiO2 inclusions. During the laser processing, the complex heating and cooling effects generated by adjacent laser tracks and by overlapping layers led to an in-situ tempering of the fresh martensite. Accordingly, the hardness values of steels in as-built condition were equivalent to those of conventionally quenched samples tempered at 350 °C and 450 °C, for gas atomized and water atomized steels, respectively. Finally, a comparison in terms of mechanical properties of the investigated steels showed that the powder atomization process resulted in limited changes in steel performance.

Microstructure and Sintering Behaviors of Al-Cr-xSi (at.%) System Alloys Processed by Spark Plasma Sintering.

In this study, microstructure and sintering behaviors of the gas-atomized Al-(25 or 30) Cr-xSi alloy (x = 5, 10 and 20 at.%) during spark plasma sintering (SPS) process were investigated. Gas-atomized alloy powders were manufactured using Ar gas atomizer process. These alloy powders were consolidated using SPS process at different temperature under pressure 60 MPa in vacuum. Microstructures of the gas-atomized powders and sintered alloys were analyzed using scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometer (EDS), and transmission electron microscopy (TEM). Hardness of the SPS sintered alloys was measured using micro Vickers hardness tester. The Al-Cr-Si bulks with high Cr and Si content were produced successfully using SPS sintering process without crack and obtained fully dense specimens close to nearly 100% T. D. (Theoretical Density). The maximum values of the hardness were 834 Hv for the sintered specimen of the gas atomized Al-30Cr-20Si alloy. Enhancement of hardness value was resulted from the formation of the multi-intermetallic compound with the hard and thermally stable phases and fine microstructure by the addition of high Cr and Si.