Gas Atomization Process Research Articles

CFD modeling of primary breakup during metal powder atomization

Powder metals are the basis of powder metallurgy with a large variety of applications, including sintering and thermal spray coatings. The Gas atomization process has been widely employed as an effective method to produce fine spherical metal powders. New applications and emerging surface technologies demand high quality powders with a very narrow particle size distribution. A computational fluid dynamics (CFD) approach is developed to examine complex fluids during atomization from different nozzle designs, using the volume of fluid (VOF) method and the Reynolds Stress Model (RSM). The modeling results show that the swirling gas atomizer is not beneficial to the atomization process while the inner-jet atomizer can improve the powder generation processing.

Reactive gas atomization processing for Fe-based ODS alloys

Gas atomization reaction synthesis was employed as a simplified method for processing oxide dispersion forming precursor Fe-based powders (e.g., Fe–Cr–Y–Hf). During this process a reactive atomization gas (i.e., Ar–O2) was used to oxidize the powder surfaces during primary break-up and rapid solidification of the molten alloy. This resulted in envelopment of the powders by an ultra-thin (t<50nm) metastable Cr-enriched oxide shell that was used as a vehicle to transport oxygen into the consolidated microstructure. Subsequent elevated temperature heat treatment promoted thermodynamically driven oxygen exchange reactions between trapped films of Cr-enriched oxide and internal (Y, Hf)-enriched intermetallic precipitates, resulting in highly stable nano-metric mixed oxide dispersoids (i.e., Y–Hf–O) that were identified with X-ray diffraction. Transmission electron microscopy and atom probe tomography results also revealed that the size and distribution of the dispersoids were found to depend strongly on the original rapidly solidified microstructure. To exploit this, several oxide dispersion strengthened microstructures were engineered from different powder particle size ranges, illustrating microstructural control as a function of particle solidification rate. Additionally, preliminary thermal–mechanical processing was used to develop a fine scale dislocation substructure for ultimate strengthening of the alloy.

Gas atomization of Cu-modified AB 5 metal hydride alloys

Gas atomization together with a hydrogen annealing process has been proposed as a method to achieve improved low-temperature performance of AB 5 alloy electrodes in Ni/MH batteries and restore the original cycle life which was sacrificed by the incorporation of copper in the alloy formula. While the gas atomization process reduces the lattice constant aspect ratio c/ a of the Cu-containing alloys, the addition of a hydrogen annealing step recovers this property, although it is still inferior to the conventionally prepared annealed Cu-free alloy. This observation correlates very well with the cycle life performance. In addition to extending the cycle life of the Cu-containing metal hydride electrode, processing by gas atomization with additional hydrogen annealing improves high-rate, low-temperature, and charge retention performances for both Cu-free and Cu-containing AB 5 alloys. The degradation mechanisms of alloys made by different processes through cycling are also discussed.

Modeling of Droplet Dynamic and Thermal Behavior during Gas Atomization Process

The paper is focused on the physical phenomena that occurs during gas atomization process, like fragmentation mechanism of the molten stream, the secondary breakup mechanism, droplets velocities and particles temperature history. The modeling of droplet dynamic and thermal history was achieved by using a software program realized by authors, called MetLAB, using the heat balance equations between the cooling gas and the molten metal droplets.

Experimental and numerical modeling of the gas atomization nozzle for gas flow behavior

Gas atomization is a widely used process for manufacturing of fine metal- and alloy-powder. To ensure a stable process with high yields of metal powder, the negative pressure at the melt delivery tube tip base and no flow separation conditions are necessary for a good atomization process. An important feature of these jets is that flow separation may occur over the outer surface of the liquid delivery tube for some conditions. Flow separation cause solidification and accumulation of metal, leading to a shape alteration of the liquid delivery tube in gas atomization process. Using computational fluid dynamics (CFD) software, a parametric study was conducted to determine the effects of atomizing gas pressure on the melt delivery tube tip base pressure and flow separation. Atomization gas pressures of 1.0, 1.3, 1.7, 2.2, and 2.7 MPa were used in the CFD model to initialize the pressure in gas inlet. CFD simulations were performed and the modeling results were compared with experimental data. These results showed that the CFD modeling can be used for the estimation of the melt tip base pressure of the nozzle. It is found that the flow separation formation is strongly dependent on the atomizing gas pressure.

Microstructural behavior of the heat treated n-type 95% Bi 2Te 3–5% Bi 2Se 3 gas atomized thermoelectric powders

In this research, n-type 95% Bi 2Te 3–5% Bi 2Se 3 doped with 0.04% SbI 3 thermoelectric powders were manufactured by gas atomization process and subsequently, the effects of rapid solidification and heat treatment on the microstructure of the powder particles were investigated. The crystal structures were analyzed by X-ray diffraction (XRD) and cross-sectional microstructures were observed by the scanning electron microscopy (SEM). The rapidly solidified powders consist of homogeneously distributed needle shape intermetallic compounds. However, the size of the intermetallic compounds increased with the increasing powder size, whereas the oxygen content in the produced powder decreased. Heat treatment of the powders for various temperatures and periods showed a significant increase in the grain size resulting in a reduction in hardness. In addition, with the increasing heat treatment temperatures and periods, the orientation factor of the powder particles decreased, which is also evident in case of the reduction treated powders.

Advanced gas atomization processing for Ti and Ti alloy powder manufacturing

A multi-layer ceramic composite melt pour tube for superheating and pouring of molten Ti-6Al-4V (wt.%) was tested using an existing Ti atomization system. Free fall gas atomization was conducted with the pour tube while liquid metal temperatures were measured in situ using a two-color optical pyrometer. Post-process pour tube erosion was compared with pre-process matching surfaces, and minimal change in interior liner thickness was found. Microstructural analysis, phase identification, and composition determination of the resulting gas-atomized powder indicated minimal contamination from the composite pour tube despite very high liquid superheat, approaching 300° C. Hot isostatic pressing of the powder resulted in mechanical properties exceeding the MIL-T-9047 standard for Ti-6Al-4V.

Study of AB 2 alloy electrodes for Ni/MH battery prepared by centrifugal casting and gas atomization

Centrifugal casting and gas atomization processes were applied on multiple phase AB 2 alloys and compared to the conventional melt-and-cast. Four different compositions were chosen for this study. The roles of Zr, Mn, Cr, and Ni in various battery aspects are identified. Cooling speed was found to be crucial for the C14 and C15 phase abundances. As the cooling speed increased from 10 2 to 10 4 degrees per second, a higher percentage of C15 was found. The centrifugal casting process provided better cycle life and low temperature performance with the only trade-off being slower activation. The gas atomization process can achieve lower production cost due to the elimination of a grinding procedure and extended cycle life, but suffers from higher bulk oxygen content and thicker surface oxide, and thus inferior in all battery performance characteristics other than cycle life and charge retention.

Development of Powder Metallurgy High Nitrogen Stainless Steel

Nitrogen alloying in steel may greatly increase the strength and corrosion resistance of the material. This paper introduced some research results of high nitrogen stainless steel (HNS) investigation via PM process. Nickel free high nitrogen stainless steels (17Cr12Mn2MoN) and superaustenitic high nitrogen stainless steels (28Cr6Mn2/6Mo10/20NiN) were investigated via gas atomization and HIP processes. Nitrogen alloying behavior during atomization and consolidation processes was investigated. Powders with nitrogen content up to 1% were manufactured by gas atomization process. Nickel free high nitrogen stainless steels with nitrogen up to 0.6% exhibits high strength and ductility at as-HIPed and solution annealed state, and superaustenitic HNS with nitrogen content up to 1% showed very high strength and good ductility at solution annealed state, with b at 1100 MPa, s at 810 MPa and elongation of 43%. PM HNS exhibited excellent corrosion resistance.

가스분무법에 의한 Fe계 비정질 분말의 제조와 볼밀링공정에 의한 연질 Cu분말과의 복합화 및 SPS 거동 (II) - II. 복합분말의 SPS와 특성 -

Fe based (Fe<TEX>$_{68.2}$</TEX>C<TEX>$_{5.9}$</TEX>Si<TEX>$_{3.5}$</TEX>B<TEX>$_{6.7}$</TEX>P<TEX>$_{9.6}$</TEX>Cr<TEX>$_{2.1}$</TEX>Mo<TEX>$_{2.0}$</TEX>Al<TEX>$_{2.0}$</TEX>) amorphous powder, which is a composition of iron blast cast slag, were produced by a gas atomization process, and sequently mixed with ductile Cu powder by a mechanical ball milling process. The Fe-based amorphous powders and the Fe-Cu composite powders were compacted by a spark plasma sintering (SPS) process. Densification of the Fe amorphous-Cu composited powders by spark plasma sintering of was occurred through a plastic deformation of the each amorphous powder and Cu phase. The SPS samples milled by AGO-2 under 500 rpm had the best homogeneity of Cu phase and showed the smallest Cu pool size. Micro-Vickers hardness of the as-SPSed specimens was changed with the milling processes.

가스분무법에 의한 Fe계 비정질 분말의 제조와 볼밀링공정에 의한 연질 Cu 분말과의 복합화 및 SPS 거동 (I) - I. 가스분무 및 복합화 -

Fe based (Fe<TEX>$_{68.2}$</TEX>C<TEX>$_{5.9}$</TEX>Si<TEX>$_{3.5}$</TEX>B<TEX>$_{6.7}$</TEX>P<TEX>$_{9.6}$</TEX>Cr<TEX>$_{2.1}$</TEX>Mo<TEX>$_{2.0}$</TEX>Al<TEX>$_{2.0}$</TEX>) amorphous powder, which is a composition of iron blast cast slag, were produced by a gas atomization process, and sequently mixed with ductile Cu powder by a mechanical ball milling process. The experiment results show that the as-prepared Fe amorphous powders less than 90 <TEX>$\mu$</TEX>m in size has a fully amorphous phase and its weight fraction was about 73.7%. The as-atomized amorphous Fe powders had a complete spherical shape with very clean surface. Differential scanning calorimetric results of the as-atomized Fe powders less than 90 <TEX>$\mu$</TEX>m showed that the glass transition, T<TEX>$_g$</TEX>, onset crystallization, T<TEX>$_x$</TEX>, and super-cooled liquid range <TEX>$\Delta$</TEX>T=T<TEX>$_x$</TEX>-T<TEX>$_g$</TEX> were 512, 548 and 36<TEX>$^{\circ}C$</TEX>, respectively. Fe amorphous powders were mixed and deformed well with 10 wt.% Cu by using AGO-2 high energy ball mill under 500 rpm.

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.

Microstructure and mechanical properties of Al–Si–X alloys fabricated by gas atomization and extrusion process

In order to develop good wear resistant and high-strength alloys, Al 81Si 19 alloy was reinforced with transition elements such as Ni and Ce. The solubility of Si in aluminum was amplified, with increasing the Ni and Ce content in the rapidly solidified powders. The extruded bars consist of homogeneously dispersed fine Si particles along with Al 3Ni and Al 3Ce compounds (30–120 nm) in aluminum matrix (grain size below 500 nm). The tensile strength at room temperature for Al 81Si 19, Al 78Si 19Ni 2Ce 0.5 and Al 76Si 19Ni 4Ce 1 bars extruded at 400 °C was estimated as 281, 521, and 668 MPa, respectively. In addition, the maximum tensile strength of 730 MPa was attained in Al 73Si 19Ni 7Ce 1 bulk alloy. The uniform dispersion of precipitates (Si, Al 3Ni and Al 3Ce particles) from the supersaturated Al matrix of ternary and quaternary alloys after extrusion was effective for enhanced mechanical properties.

Effect of rapid solidification on the microstructure and mechanical properties of hot-pressed Al–20Si–5Fe alloys

The aim of this work is to study the effect of cooling rate and subsequent hot consolidation on the microstructural features and mechanical strength of Al–20Si–5Fe–2X (X = Cu, Ni and Cr) alloys. Powder and ribbons were produced by gas atomization and melt spinning processes at two different cooling rates of 1 × 10 5 K/s and 5 × 10 7 K/s. The microstructure of the products was examined using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The particles were consolidated by hot pressing at 400 °C/250 MPa/1 h under a high purity argon atmosphere and the microstructure, hardness and compressive strength of the compacts were evaluated. Results showed a profound effect of the cooling rate, consolidation stage, and transition metals on the microstructure and mechanical strength of Al–20Si–5Fe alloys. While microstructural refining was obtained at both cooling rates, the microstructure of the atomized powder exhibited the formation of fine primary silicon (~ 1 μm), eutectic Al–Si phase with eutectic spacing of ~ 300 nm, and δ-iron intermetallic. Supersaturated Al matrix containing 5–7 at.% silicon and nanometric Si precipitates (20–40 nm) were determined in the microstructure of the melt-spun ribbons. The hot consolidation resulted in coarsening of Si particles in the atomized particles, and precipitation of Si and Fe-containing intermetallics from the supersaturated Al matrix in the ribbons. The consolidated ribbons exhibited higher mechanical strength compared to the atomized powders, particularly at elevated temperatures. The positive influence of the transition metals on the thermal stability of the Al–20Si–5Fe alloy was noticed, particularly in the Ni-containing alloy.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF HYPEREUTECTIC Al-Si/AlNp COMPOSITE

Hypereutectic Al - Si alloys with fine and evenly distributed Si precipitates have superior mechanical properties In this study, hypereutectic Al - Si alloy powders which contained 15 and 20wt% Si were prepared by a gas atomization process. 1, 3 and 5wt% AlN particles were blended with the Al - Si alloy powders using turbular mixer. The mixture was consolidated by Hot Press at 550°C for 1h under 60MPa. Relative density of the sintered samples was about 98% of theoretical density. This study was investigated by two ways. One is the effect of reinforcement weight fraction and the other is the effect of Silicon contents on the mechanical properties of the composite. Microstructural characterization and phase evaluation were carried out using X-ray Diffraction, Scanning Electron Microscopy equipped with Energy Dispersive Spectrometer. The results showed that the smaller the reinforcement particle size was and the better its distribution was, the higher ultimate tensile strength and hardness were.

コールドスプレーによるナノ準結晶粒子分散アルミニウム合金皮膜の作製

It is known that quasicrystalline phases have high Vickers hardness and high thermal stability. Heat-resistant aluminum alloys, which contain dispersed nanoscale quasicrystalline particles and have very high tensile strength at highly elevated temperatures (473 to 673 K), were developed in 2006. We aimed to partially strengthen components using the developed material as a coating material. However, the general spraying technology, if used, would expose this coating material to high temperatures, causing the quasi-crystalline phase to decompose into an intermetallic compound phase. In this study, aluminum alloy coatings containing dispersed nanoscale quasicrystalline particles have been produced using the cold spray method, which can be performed at comparatively lower temperatures. Rapidly solidified powder was produced by the atomization method, which consists of a combined high-pressure gas atomization and water atomization process. The cold spray process was carried out on nitrogen or helium gas at 3 MPa and 673 K. As a result of X-ray analysis and DSC measurement, it was ascertained that the dispersed quasicrystalline structure is maintained even after the cold spray coating process. Also from TEM observation, the dispersed quasicrystalline structure was maintained within the coating.

Pitting Resistance of Al90Fe7Nb3 and Al90Fe7Zr3 Nanocrystalline Alloys Obtained by Melt-Spinning and Hot Extrusion

Amorphous and/or nanocrystalline Al-based alloys have better mechanical properties when compared with crystalline conventional Al-alloys. Different techniques can be used to obtain amorphous Al-based alloys, usually in a ribbon form (from melt-spinning processing) or powders (from gas atomization or ball milling processing). To obtain bulk samples, that is, samples with dimensions typically much larger (mm scales) than the ones obtained from the above mentioned techniques (<40 μm), the ribbons or powders must be hot-consolidated. One of the most important challenges in the development of such alloys is to keep a refined microstructure after the necessary heating. The present work focuses the pitting resistance by electrochemical corrosion resistance test in solution 0.9 % NaCl and pH 7.0, for Al 90 Fe 7Nb 3 and Al 90 Fe 7Zr 3 nanocrystalline alloys, which were obtained by hotextrusion of mechanically alloyed powders, and melt-spinning process. The results of the polarization curves indicated that the Al 90 Fe 7Nb 3 and Al 90 Fe 7Zr 3 ribbons present better corrosion properties than the extruded alloys.

Microwave-induced sintering of NiNbTiPt metallic glass blended with Sn powders using a single-mode applicator

Microwave (MW) processing is emerging as an innovative and highly effective material processing method offering many advantages over conventional methods especially for sintering application. In the present study, using a mixed powder of the Ni55Nb25Ti15Pt5metallic glassy powder prepared by an argon gas atomization process blended with 50 vol.% Sn powder, the MW-induced heating and sintering were carried out by a single-mode 2.45 GHz MW applicator in a magnetic field maximum. The structure and thermal stability of the sintered glassy composite specimens were investigated. The addition of Sn particles enhanced densification of the sintered Ni-based metallic glassy alloy powders.

Synthesis and densification of Cu added Fe-based BMG composite powders by gas atomization and electrical explosion of wire

In this study, the Fe-based (Fe–C–Si–B–P–Cr–Mo–Al) BMG powders were produced by the high pressure gas atomization process, and they were combined with the ductile Cu powders produced by the electrical explosion of wire (EEW). The Fe-based amorphous powders and Cu added BMG composite powders were compacted by the spark plasma sintering (SPS) processes into cylindrical shape. In the SPS press, the as-prepared powders were sintered at 793 K and 843 K. The relative density increased to 98% when the pressure increased up to 500 MPa by optimum control of the SPS process parameters. The micro-Vickers hardness was over 1100 Hv.

가스분무 Fe계 비정질 분말과 유체 내 전기선 폭발에 의한 나노 Cu 분말의 복합화와 방전플라즈마 소결

Fe based (<TEX>$Fe_{68.2}C_{5.9}Si_{3.5}B_{6.7}P_{9.6}Cr_{2.1}Mo_{2.0}Al_{2.0}$</TEX>) amorphous powder were produced by a gas atomization process, and then ductile Cu powder fabricated by the electric explosion of wire(EEW) were mixed in the liquid (methanol) consecutively. The Fe-based amorphous - nanometallic Cu composite powders were compacted by a spark plasma sintering (SPS) processes. The nano-sized Cu powders of <TEX>${\sim}\;nm$</TEX>200 produced by EEW in the methanol were mixed and well coated with the atomized Fe amorphous powders through the simple drying process on the hot plate. The relative density of the compacts obtained by the SPS showed over 98% and its hardness was also found to reach over 1100 Hv.