Gas-atomized Particles Research Articles

Tunable magnetic and magnetocaloric properties by thermal annealing in ErCo2 atomized particles

Processing magnetocaloric materials into magnetic refrigerants with appropriate shapes is essential for the development of magnetic refrigeration systems. In this context, the impact of processing on the physical properties of the materials is one of the important issues. Here, we investigate the crystallographic, magnetic, and magnetocaloric properties of gas-atomized particles of the intermetallic compound ErCo2, a giant magnetocaloric material for low-temperature applications. The results demonstrate that the physical properties of ErCo2 are significantly changed by atomization and subsequent thermal annealing. In the as-atomized particles, the magnetic transition temperature increases from 34 to 56 K, and the phase transition changes from first order to second order. The thermal annealing shifts the transition temperature back to the original one and restores the first-order phase transition characteristic. The changes in magnetic properties are closely related to those in crystallographic properties, suggesting the importance of the magneto-structural coupling. The magnetic entropy change −ΔSM of the particles can be tuned in size, shape, and peak temperature depending on the annealing conditions. The peak value of −ΔSM varies in the range of 9–33 J kg−1 K−1 for a field change of 0–5 T. All the ErCo2 atomized particles have magnetocaloric properties comparable or superior to other promising candidates for low-temperature magnetic refrigerants.

Experimental characterization of CH4 and CO2 hydrates formation in presence of porous quartz and Cu gas-atomized particles: Thermodynamic analyses and evidences about the feasibility of CH4/CO2 reverse replacement

Methane and carbon dioxide hydrates were formed in a small-scale apparatus filled with pure quartz porous sand and Cu particles, produced via gas-atomization for applications in additive manufacturing. Three different concentrations were tested, of 4.23, 18.01 and 30.66 wt%. This additive was found to act as promoter for methane hydrates and as inhibitor for carbon dioxide hydrates. The effect increased with the concentrations and was associated to the chemical properties of particles. Results were compared validated with literature. For the first time, it was possible to add this material to the group of additives able to intervene on the process differently as a function of the guest compound involved. Results showed a thermodynamic area in which CO2 hydrates required more severe conditions than CH4 hydrates to form. This new configuration allowed to propose an innovative application based on the CH4/CO2 reverse replacement.

Effect of Non-Stoichiometry on Magnetocaloric Properties of HoB2Gas-Atomized Particles

We fabricate gas-atomized particles by inductively melting electrode rods of HoB2-x (x = -0.3, 0, 0.3, and 1.0) and investigate the effect of non-stoichiometry on the phase fraction, microstructure, and physical properties. Shifting the stoichiometric ratio of the electrode rod to the B (Ho)-rich side increases HoB4 (Ho) phase in the resulting atomized particles. Even if the atomized particles contain 15-20 weight percent (wt.%) of the impurity phase, the influence of which on the physical properties is less severe: the maximum value of the magnetic entropy change is only reduced by 10% compared to HoB2.0 particles. We further find that the ductile Ho phase exists so as to fill the space between the brittle HoB2 phases in the atomized particles, which may be beneficial to the mechanical properties of the particles. Our findings suggest that it would be better to use the Ho-rich electrode rods than the stoichiometric ones to produce HoB2-x particles with more suitable properties as a magnetic refrigerant for magnetic refrigeration systems.

Functional, thermal and rheological properties of polymer-based magnetic composite filaments for additive manufacturing

The design of functional composite filaments for fused filament fabrication requires a suitable polymer composition, functionality of particles, uniform distribution of fillers throughout the filament, and adequate printability. Uniform distribution at predictable concentrations is achieved by designing polymeric capsules containing the fillers and using them as feedstock for extrusion. Functionality can be inferred from that of the particles and target concentration. However, suitable conditions for printing strongly depend on polymer type and characteristics/concentration of fillers. Soft magnetic composite filaments were produced from polylactic acid (PLA) capsules filled with 30–52 wt. % maraging steel particles. Composite filaments preserve the soft magnetic character of the fillers. Fillers reduce the transition temperatures of the polymer by ∼ 5 K and have a profound impact on printability. Rheological characterization shows that the “ball bearing effect” of gas-atomized particles reduces the viscosity of the composites by more than one order of magnitude, decreasing printing temperature from 215 °C to 170 °C, associated with the lack of agglomeration of particles achieved by the proposed production method. Rheological experiments allow to detect the required changes in printing conditions without requiring an extensive and costly trial and error process of printing with a large set of printing parameters.

Magnetocaloric particles of the Laves phase compound HoAl2 prepared by electrode induction melting gas atomization

Processing magnetocaloric materials into magnetic refrigerant particles is an essential issue in developing high-performance magnetic refrigerators. Here, we succeed in stably producing magnetocaloric particles of the promising material HoAl2 by a newly devised method based on electrode induction melting gas atomization process. The particle size range is on the order of submillimeters, which is suitable for practical refrigeration systems. The resulting particles with less contamination have good morphological, magnetic, and magnetocaloric properties: (i) almost spherical shapes with few internal pores, (ii) a sharp ferromagnetic transition around 30 K, and (iii) a large magnetocaloric effect comparable to the bulk counterpart. These features suggest the HoAl2 gas-atomized particles have the potential of use as a magnetic refrigerant. The presented method can be applied not only to HoAl2 but also to other brittle magnetocaloric materials with high melting points, facilitating the production of various magnetic refrigerants needed to develop magnetic refrigerators for hydrogen liquefaction.

Gas-atomized particles of giant magnetocaloric compound HoB$$_{2}$$ for magnetic hydrogen liquefiers

The processing of promising magnetocaloric materials into spheres is one of the important issues on developing high-performance magnetic refrigeration systems. In the present study, we achieved in producing spherical particles of a giant magnetocaloric compound HoB2 by a crucible-free gas atomization process, despite its high melting point of 2350 C. The particle size distribution ranges from 100 to 710 micrometers centered at 212-355 micrometers with the highest yield of 14-20wt% of total melted electrode, which is suitable for magnetic refrigeration systems. The majority of the resulting particles are mostly spherical with no contamination during the processing, while unique microstructures are observed on the surface and inside. These spherical particles exhibit sharp magnetic transitions and huge magnetic entropy change of 0.34 J cm^{-3} K^{-1} for a magnetic field change of 5 T at 15.5 K. The high sphericality and the high magnetocaloric performance suggest that the HoB2 gas-atomized particles have good potential as magnetic refrigerants for use in magnetic refrigerators for hydrogen liquefaction.

Effect of electro-codeposition parameters on particle incorporation in Ni-CrAlY(Ta) coatings

ABSTRACT Electrolytic codeposition is a promising alternative low-cost process for fabricating MCrAlY coatings. In this process, CrAlY particles are codeposited with the (Ni,Co) to form an (Ni,Co)-CrAlY composite coating, which is subsequently heat treated at elevated temperatures to be transformed to the MCrAlY coating containing phases of β-NiAl, γ-(Ni,Co), etc. A permeable rotating barrel was utilized in the present electro-codeposition process, which offered the benefit to apply uniform coatings on the entire sample surface. Such codeposition configuration allowed exchange of electrolyte between the barrel and the plating tank while keeping the specimen and powder inside the barrel. Two types of CrAlY-based particles (made by ball milling and gas atomization) were employed. The effects of several key processing parameters, such as current density, particle loading, and barrel rotational speed, on the CrAlY(Ta) particle incorporation in the electrodeposited Ni-CrAlY(Ta) coatings were studied. The influence of particle geometry/shape was also investigated. Higher CrAlY particle incorporation was observed for the spherical gas-atomized particles than the ball-milled particles with irregular shapes.

Effect of Short Attritor-Milling of Magnesium Alloy Powder Prior to Spark Plasma Sintering.

The spark plasma sintering (SPS) technique was employed to prepare compacts from (i) gas-atomized and (ii) attritor-milled AE42 magnesium powder. Short attritor-milling was used mainly to disrupt the MgO shell covering the powder particles and, in turn, to enhance consolidation during sintering. Compacts prepared by SPS from the milled powder featured finer microstructures than compacts consolidated from gas-atomized powder (i.e., without milling), regardless of the sintering temperatures in the range of 400–550 °C. Furthermore, the grain growth associated with the increase in the sintering temperature in these samples was less pronounced than in the samples prepared from gas-atomized particles. Consequently, the mechanical properties were significantly enhanced in the material made of milled powder. Apart from grain refinement, the improvements in mechanical performance were attributed to the synergic effect of the irregular shape of the milled particles and better consolidation due to effectively disrupted MgO shells, thus suppressing the crack formation and propagation during loading. These results suggest that relatively short milling of magnesium alloy powder can be effectively used to achieve superior mechanical properties during consolidation by SPS even at relatively low temperatures.

Study of phases evolution in high-coercive MnAl powders obtained through short milling time of gas-atomized particles

Abstract Gas-atomized Mn 54 Al 46 particles constituted nominally of only e- and γ 2 -phases, i.e. no content of the ferromagnetic L1 0 -type τ-phase, have been used to study the evolution of phases during short time of high-energy milling and subsequent annealing. Milling for 3 min is sufficient to begin formation of the τ-MnAl phase. A large coercivity of 4.9 kOe has been obtained in milled powder after annealing at 355 °C for 10 min. The large increase in coercivity, by comparison with the lower value of 1.8 kOe obtained for the starting material after the same annealing conditions, is attributed to the combined formation of the τ-MnAl and β-Mn phases and the creation of a very fine microstructure with grain sizes on the order of 20 nm. Correlation between morphology, microstructure and magnetic properties of the rapidly milled MnAl powders constitutes a technological advance to prepare highly coercive MnAl powders.

Microstructure simulation of rapidly solidified ASP30 high-speed steel particles by gas atomization

In this study, the microstructure evolution of rapidly solidified ASP30 high-speed steel particles was predicted using a simulation method based on the cellular automaton-finite element (CAFE) model. The dendritic growth kinetics, in view of the characteristics of ASP30 steel, were calculated and combined with macro heat transfer calculations by user-defined functions (UDFs) to simulate the microstructure of gas-atomized particles. The relationship among particle diameter, undercooling, and the convection heat transfer coefficient was also investigated to provide cooling conditions for simulations. The simulated results indicated that a columnar grain microstructure was observed in small particles, whereas an equiaxed microstructure was observed in large particles. In addition, the morphologies and microstructures of gas-atomized ASP30 steel particles were also investigated experimentally using scanning electron microscopy (SEM). The experimental results showed that four major types of microstructures were formed: dendritic, equiaxed, mixed, and multi-droplet microstructures. The simulated results and the available experimental data are in good agreement.

Criterion of gas and solid dual-phase flow atomization crash in molten metal

A self-invented atomization process, in which molten metal is atomized into powder by a high-velocity gas stream carrying solid particles as the atomization medium, was introduced. The characteristics of powders prepared by common gas atomization and dual-phase flow atomization under similar conditions were compared. The experimental results show that the dual-phase flow-atomized powders have average particle sizes that are one-half that of the common gas-atomized particles; additionally, they possess a finer microstructure and higher cooling rate under the same atomization gas pressure and the same gas flow. The Weber number in the crash criteria of liquid atomization is adopted to measure the crash ability of the atomization media. The Weber number of the dual-phase flow atomization medium is the sum of that of the gas and the solid particles. Furthermore, the critical equation of the crash model in dual-phase flow atomization is established, and the main regularities associated with this process were analyzed.

Lead Free Paste with under 3um Solder Particles for Fine Pitch C4 bumping and pre-coating solder applications

The work to be detailed in this paper is our development of 96.5mass%Sn-3.0mass%Ag-0.5mass%Cu fine solder particles with an average particle size of under 3um (D50), using a chemical reduction method. An evaluation was conducted on the properties of the particles. The average size of particles appeared to be under 3um with a higher yield compared to particles using the conventional gas atomization method. The melting temperature of fine solder particles using this method was its eutectic temperature, which is same as using the gas–atomized particles. 120um pitch solder bumps from the solder paste using the above mentioned fine solder particles were created on the substrate. As a result of property evaluation, it was turned out that the solder paste created a superior printing shape and coplanarity compared to the conventional paste with gas-atomized particles. In order to investigate the superior printing property generated by the paste with fine solder particles, the rheology of the paste was evaluated.It was verified that the anisotropic shape of particles has contributed to prevent the printed paste from slumping, which has resulted in the improvement of printed shape. It also shows that the filling characteristic of the paste was improved by the smaller particles and the better coplanarity was observed. The importance of finer solder particles for finer pitch assembly will be presented.

Hydriding behavior in Zr-based AB 2 alloy by gas atomization process

The hydriding characteristics of Zr-based AB 2 alloy produced by gas atomization have been investigated during its absorption–desorption reaction with hydrogen gas. Its gas-phase hydrogenation properties are different from those of specimens prepared by conventional methods. For the particle morphology of the as-cast and gas-atomized powders, it can be seen that the mechanically crushed powders are irregular, while the atomized powder particles are spherical. In PCT (Pressure–Composition–Temperature) measurements, for the gas-atomized particles smaller than 50 μm, the hydrogen storage capacity is dramatically decreased and the hysteresis loop becomes larger than that of the gas-atomized particles larger than 50 μm. In addition, the increase of jet pressure of gas atomization results in the decrease of hydrogen storage capacity and the slope of plateau pressure significantly increases. TEM and EDS studies showed the increase of jet pressure in the atomization process accelerated the phase separation within grain of the gas-atomized alloy, which brought about a poor hydrogenation property. In the measurements of hydrogen absorption–desorption kinetics, the improvement of desorption kinetics of gas-atomized AB 2 alloys was mainly caused by the higher plateau pressure, which is attributed to the smaller grain size and higher site energy for hydrogen in the gas-atomized alloys.

The microstructure of Fe–Ga powders and magnetostriction of bonded composites

Spherical Fe–Ga particles were prepared by gas atomization. The Ga concentration of gas-atomized particles approached the nominal composition of Fe 81 Ga 19 . Most size fractions of particles had a polycrystalline structure. The main A2 phase and a DO 3 phase emerged in the as-atomized powders. The L1 2 phase appeared in the annealed powders. Many single crystals were obtained due to grain growth during the thermal process. The maximum saturation magnetostriction of 6.4 × 10 −5 was obtained in the composite containing the annealed powders.

Effect of particle size on hydrogenation properties of a gas-atomized AB 5-type alloy

The effect of particle size on the hydrogenation properties of gas-atomized MmNi 3.6Co 0.56Mn 0.56Al 0.28 was investigated. Its gas-phase and electrochemical hydrogenation properties are different from those of specimens prepared by conventional methods. The initial shape of the alloy particles is spherical. After hydrogenation, significant changes take place in the larger particles. They become irregular, and a fresh surface is created. For particles smaller than 10 μm, no cracks are observed and they can hardly react with hydrogen gas. For particles larger than 10 μm, the gas-phase hydrogenation rate is faster than for the smaller particles, but the P–C–T curves are about the same. As regards electrochemical behavior, 75–38-μm particles have the highest discharge capacity (282 mAh/g). For the particles smaller than 38 μm, the maximum capacity decreases to 238 mAh/g. The maximum capacity of the particles smaller than 10 μm is only ∼8 mAh/g. If the particles smaller than 10 μm are excluded, i.e. for particles in the range 38–10 μm, the discharge capacity increases to 268 mAh/g. It is concluded that 10 μm is a critical size for practical application of gas-atomized particles. Surface characterization of the particles of different sizes explains the inferior performance of the smaller particles.

Gas Atomization Processing of LaNi5-x.Mm, Modified with Silicon and Tin

ABSTRACTA high pressure gas atomization (HPGA) process has been employed to study microsegregation in LaNi4.75 Sn0.25 and LaNi4.6Si0.4 alloy powders to serve as a basis for further investigations of low cost production of multicomponent alloys in combination with mishmetal (Mm). This investigation is an attempt to produce high quality powders for battery cathode fabrication that can be used in an as-atomized condition without prolong annealing, hydridingdehydriding, and grinding. Argon atomizing gas was used in the HPGA process of the LaNi4.75Sn0.25 and LaNi4.6Si0.4 alloys to investigate rapid solidification effects on microsegregation. Short annealing treatments of 5 minutes at 900°C were able to homogenize both alloy compositions, eliminating solidification micro-segregation along the grain boundaries phases. The rapid homogenization can be attributed primarily to the refined cell structures in gas-atomized particles that provide short diffusion pathways for the dissolving elements.