Gas Atomization Method Research Articles

Bulk Mg2Si Based n-type Thermoelectric Material Produced by Gas Atomization and Hot Extrusion

Bulk thermoelectric (TE) materials for large scale energy harvesting applications need to demonstrate not only high TE performance, but should also be composed from elements which are nontoxic, largely available in nature, and preferably be as light as possible for applications such as automobiles. Magnesium silicide based materials possess a combination of these properties and are among the best candidates for these applications. For the successful implementation of Mg2Si based alloys, all material manufacturing steps have to be compatible with the requirements of mass production. We report two processes to manufacture these alloys which can be easily scaled up: (i) a gas atomization method for powder production, followed by (ii) hot extrusion to obtain bulk specimens. The Mg2Si1-xSnx (0.3 ≤ x≤ 0.7) powders were prepared by gas atomization using a stoichiometric mixture of the commercially available high purity elements. Particle size distribution analysis shows that 90% of particles thus obtained have sizes ranging from 10 to 100μm with a mean value of 46.5μm. Hot extrusion was carried out for Mg2Si0.4Sn0.6 composition at 450-480°C and 500-550°C applying pressures up to 1GPa. Addition of 4 vol% of nanometre sized MoS2 particles in the powder facilitates material densification. Specimens extruded at temperature range of 500-550°C demonstrate 99.7% of the theoretical density. The TE properties were studied by the Harman method between 300 K and 700 K. The Seebeck coefficient varies from -150 to -220μV/K, passing through a maximum value at 450K. The electrical conductivity of 88 S/cm at 300 K increases with temperature showing a typical behavior for under-doped TE material. The ZT value reaches a maximum of 0.08 at 620 K. Our work shows that implementation of a gas atomization process for powder production combined with hot extrusion, as a densification and sintering method, can be successfully implemented for bulk Mg2Si1-xSnx manufacturing. This approach to obtain Mg2Si based alloys, once optimized, has a great potential for large scale waste heat recovery applications.

Enhanced properties of an AA7075 based metal matrix composite prepared using mechanical alloying

In this study, firstly, AA7075 metal powder which average particle size 43.9 µm were manufactured by using gas atomization method. Thereafter with mechanical alloying method which powder metallurgy manufacturing methods, 10% B4C particle reinforcements that average particle size of 49.5 µm by participating into AA7075 metal matrix composite powder mixtures were prepared. They were milled for different durations (0-8 hrs) in a high energy planetary ball mill. From these milled powders; 550°C and under pressure 500 MPa, composite materials were produced by the method of hot pressing. In SEM analysis, after 4 hrs with mechanical alloying method, B4C particles which were homogenously distrubuted into the matrix of AA7075 were seen. Powders size increased to 1 hr and then decrease. In order to determine produced composite material's microstructural properties SEM analysis and determine physical and mechanical properties, density test and hardness test was applied. As a result of the experiments, composite density increased to 1 hr and then decrease. The hardness of composite was increased with increasing milling time and the rate of reinforcement.

Improvements of dry sliding wear behaviour and mechanical properties in 2014 Al alloy by age-hardening

In this study AA 2014 powder metal alloy was produced by using the vertical gas atomization method. In the post-production stage, by unidirectional pressure in the steel mould, the powders were converted into powder metal samples. The derived powder metal particles from the micro structural point were subjected to sintering process for 1 h at the temperature range of 550 and 620°C. Next, the samples were exposed to heat treatment at the temperature interval of 2 to 192 h in 500 and 600°C. For aging heat treatment, water quenching process post-solution treatment at 520EsC was applied to these samples. Afterwards, these samples were applied to aging process at 150°C on the condition of the range of 4 to 24 h, and up to 70% increase in hardness was determined. Finally, through an examination of dry fictional wear behaviours of samples processed at 550 and 600°C, oxide occurrence with increasing heat was observed to effect wear loss and wear loss was identified not to be linear as the distance raised. Key words: Wear, age-hardening, 2014 Al alloy.

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.

Structural and magnetic properties of the gas atomized Mn-Al alloy powders

Ferromagnetic Mn-Al powders were produced by a gas-atomization method followed by heating treatment. The gas-atomized powders were E >-phase, which is a high temperature phase in the Mn-Al system. The E >-tau phase transformation took place by subsequent heat treatment at temperatures from 500 to 700 A degrees C. The gas-atomized powders with a smaller particle size formed the tau-phase faster and thus exhibited better magnetic properties. On the other hand, the annealing temperature and time similarly played important roles in determining the magnetic properties of the products. The Mn-Al powders of 25-38 mu m annealed at 550 A degrees C for 120 min exhibited a high coercivity of 3.2 kOe with a remanence of 38 emu/g.

Liquid-immiscibility-induced formation of micron-scale crystalline/amorphous composite powder

Liquid immiscible alloy systems present a unique opportunity in developing the micron-scale crystalline/amorphous composite powder using the gas atomization method. On the basis of the CALPHAD approach, the compositions of Co–Si–B–Cu alloys system exhibiting the liquid immiscibility have been designed. The produced gas-atomized powders show a Cu-rich crystalline/Co–Si–B rich amorphous composite microstructure. The above-mentioned powders possess almost the same coercive force as that of Co–Si–B amorphous powders, while their saturation magnetization decreases with increasing Cu concentration. Such Cu-rich crystalline/Co–Si–B rich amorphous composite powders may have applications in the field of heat release of soft magnetic devices and ferrofluids.

Consolidation of Cu based amorphous powder by hot pressing method

Amorphous Cu50Zr40Ti10 powder was fabricated in the particle size range <50 μm by gas atomisation method. Gas atomised Cu50Zr40Ti10 amorphous powder exhibits the glass transition temperature Tg of 629·5 K and the crystallisation temperature Tx of 693·2 K respectively. The gas atomised Cu50Zr40Ti10 amorphous powder possesses a high supercooled liquid region ΔTx of 63·7 K suitable for being hot pressed. In addition, the Cu50Zr40Ti10 amorphous powders were consolidated by hot pressing method based on an L9(34) orthogonal design. The optimum consolidation condition for the Cu50Zr40Ti10 amorphous powder is first precompacted under the pressure of 75 MPa, and then consolidated under the pressure of 450 MPa at the temperature of 380°C respectively. The significance of three factors is examined by the analysis of variance for the density and thermal conductivity respectively. The effect of three factors on the density and thermal conductivity is also discussed.

Super Fine Lead-Free Solder Powder for Fine Pitch Bump Applications

We have successfully developed super fine lead-free and low alpha solder powder, which contains more than two elements by the method of wet chemical reduction. The size (D50) of super fine powder is around 2–3 micrometer to meet finer pitch assembly in the near future. This new method made it available to synthesize various compositions of solder powder like Sn-Ag, Sn-Cu, Sn-Ag-Cu, etc. Also, this method achieves very high yield compared to a gas atomization method. A solder paste for printing method composed of the fine solder powder has a superior printing ability because of the unique powder shape. The powder shows anisotropic shape, and it can make printed figure excellent after printing without bridge and coplanarity issues for finer pitch applications. With our super fine solder paste, we will be ready for &amp;lt;100um pitch of solder bumps which will come in a few years. Furthermore, the super fine powder is applied to the Cu pad pre-coat. The solder paste for pre-coat composed of the super fine powder shows an excellent coverage and solders flatness on the outer pad after reflow.

Preparation, characterization and microwave absorbing properties of FeNi alloy prepared by gas atomization method

In this work, Fe–50 wt%Ni alloy was synthesized by nitrogen gas atomization method. The phase composition, morphology, element composition and saturation magnetization of the alloys were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence spectrometer (XRF) and vibrating sample magnetometer (VSM). The electromagnetic parameters and microwave absorbing properties of the microwave absorbing material made from silicone rubber and the as-prepared FeNi alloy were also studied using vector network analyzer (VNA) and transmission line theory. The results show that the particle size of most of the particles is less than 150 μm, and the average particle size is about 48 μm. The Fe–50 wt%Ni powder has a spherical shape, and the main phase composition is FCC (Fe, Ni) alloy. The as-atomized FeNi alloy possesses low coercivity and high specific saturation magnetization. As the frequency increases, the real part of relative permittivity and relative permeability of the Fe–50 wt%Ni/silicone rubber absorber decrease, while the imaginary part of relative permittivity increases. The Fe–50 wt% Ni alloy/silicone rubber absorbers with 0.8–4 mm thickness exhibit adjustable microwave absorbing properties in the range of 1–18 GHz.

Mechanical and Electrical Properties of Rapidly Solidified Cu-Zr-Ag Alloy Fabricated by Powder Rolling Process

ABSTRACTA non-equilibrium Cu-Zr-Ag alloy was designed for the development of an alternative electric connector to Cu-Be alloys. This work aims at producing a Cu-Zr-Ag sheet using a hot-powder-rolling (HPR) process. The sheets were produced by a sequential process of HPR, pre-annealing, and cold rolling, using Cu93.5Zr5.5Ag1 (at.%) alloy powder produced by an argon gas atomization method. The Cu93.5Zr5.5Ag1 alloy sheet has a tensile strength of 1188 MPa and a conductivity of 33.2% IACS, which are similar values to those of Cu-Be alloys. In this paper, we optimize the conditions of the HPR process and reveal the correlation between the microstructure and properties of the Cu-Zr-Ag sheet produced by the HPR process. In addition, we discuss the alloy’s applicability for use as a connecter material.

Effect of different copper fillers on the electrical resistivity of conductive adhesives

The effects of different copper fillers with different morphology and particle size have been studied in terms of electrical resistivity and thermal stability on the electrically conductive adhesives. The copper fillers used in this study were prepared by wet chemical reduction, electrolytic and gas atomization method, respectively. The as cured ECAs filled with different type of Cu fillers showed significant difference in electrical resistivity. Cu filler with smaller particle size showed higher packing density and larger surface area, which would enhance formation of conductive channels and increased conductive network in the ECAs, leading to a lower electrical resistivity. In addition, thermal stability of the ECAs were investigated under high temperature exposure at 125 °C and high humidity aging at 85 °C/85% RH for 1,000 h. Results showed that ECAs with Cu fillers of relatively small particle size and rough particle surface have excellent thermal stability due to enhanced adhesion and contact area between Cu fillers and the polymer matrix. A very low resistivity at an order of magnitude of 10−4 Ω cm could be maintained for these ECAs after 1,000 h at 125 and 85 °C/85% RH.

Martensitic Transformation in NiCoMnSn Metamagnetic Shape Memory Alloy Powders

Martensitic and magnetic properties of NiCoMnSn metamagnetic shape memory alloy powders obtained by a gas atomization method were investigated. The as-atomized powders showed a dendritic structure which changed to a single-phase one by annealing at 1173 K for 2 h. Although the martensitic transformation behavior was almost the same as that in bulk samples, the transformation thermal interval, namely, M s - M f , of the as-annealed powders decreased with increasing annealing time. In the powders annealed at 1173 K for 144 h, a reversible metamagnetic phase transition was confirmed by the application of a magnetic field of 7 T.

Structure Effect of Si-Based Powder on Cycle Performance of Lithium Ion Battery

In this study, an inactive material (Ni) is introduced into Si for buffering the volume change causing by the lithium insertion and de-insertion. A porous structure is designed for further reducing of the volume change. The surface-porous structure SiNi powder is prepared by gas atomization method and wet-etching in an acidic solution, which shows positive effects on cycle performance, high capacity and the efficiency at the first cycle. Coated a carbon layer onto SiNi powders by CVD process can further improve the cycle performance by preventing structure collapse.

Fabrication of Rod type Cu&lt;sub&gt;54&lt;/sub&gt;Ni&lt;sub&gt;6&lt;/sub&gt;Zr&lt;sub&gt;22&lt;/sub&gt;Ti&lt;sub&gt;18&lt;/sub&gt; Bulk Amorphous Alloy by Warm Extrusion Process

In this study, rod type Cu54Ni6Zr22Ti18 bulk amorphous alloy fabricated by warm extrusion of amorphous powders was investigated. To get bulk type amorphous alloy, the Cu54Ni6Zr22Ti18 amorphous powders which has a particle size below 63( and wide supercooled liquid region of 53K were prepared by a high-pressure gas atomization method. The powders were filled in a Cu can with an inner dimension 20×2×50mm in air, evacuated, sealed and then precompacted in the press. Before extrusion, the billet was heated with heating rate of 50K/min and the holding time was about 5min. The extrusion temperature was 723K and the extrusion ratio was increased from 2 to 5. By warm extrusion of amorphous powders, a fully amorphous Cu54Ni6Zr22Ti18 bulk type alloys were successfully synthesized. The conditions for extrusion were decided based on the time-temperature-transformation curve and DSC analysis. Phase analysis was performed by XRD. The result of the phase analysis indicated that Cu54Ni6Zr22Ti18 bulk rod type samples having fully amorphous phase could be obtained until extrusion ratio of 4 at extrusion temperature of 723K, but partial crystalline phase would be observed in the bulk rod type alloy fabricated at extrusion ratio of 5.

The influence of the pressure formation at the tip of the melt delivery tube on tin powder size and gas/melt ratio in gas atomization method

The production of metal powder using gas atomization technique is a wide spread process for manufacturing a wide range of spherical metal powder alloys. Metal powder properties generally improve with smaller powder particle size. Close-coupled atomizers are of great interest and controlling their performance parameters is critical for metal powder producing industries. In this study a new designed close-coupled nozzle system was used to produce tin powder to investigate the effect of the protrusion length of the melt delivery tube on the pressure formation at the melt tip. Observed improvement in particle refinement cannot be directly attributed to an increase in atomizing pressures and gas kinetics. Results from this study indicated that the observed metal flow rate was not behaving as what was earlier assumed, namely that, deeper aspiration enhanced metal flow rate. The melt flow rate was reduced with increasing the atomizing gas pressure. So that gas to melt mass flow ratio was increased for the same protrusion length and this ratio increase caused the finer powder particle size.

Amorphous and nanostructured Al 85Ni 5Y 6Co 2Fe 2 powder prepared by nitrogen gas-atomization

Al 85Ni 5Y 6Co 2Fe 2 fully amorphous and partially amorphous powders were prepared by nitrogen gas-atomization method. The microstructure and thermal stability as a function of powder size were investigated. A majority of the powders are below 45 μm, and the content of amorphous phase is as high as 97.3% in the <25 μm size range. With the increase of particle size, the phase constituent alters from amorphous to amorphous’ + fcc-Al, then fcc-Al + AlNiY + Al 3(Ni, Fe), and finally fcc-Al + Al 9Co 2 + Al 3Y + Al 3(Ni, Fe). All of the powders show three exothermic reactions in the DSC traces, and the <25 μm size range presents a wide supercooled liquid region of 22 K and a primary crystallization temperature of 580 K. The Al 85Ni 5Y 6Co 2Fe 2 alloy powders exhibit a high microhardness of near 348 Hv, suggesting its good potential for structural application.

Microstructure and mechanical properties of Cu-based bulk amorphous alloy billets fabricated by spark plasma sintering

In this study, Cu-based bulk amorphous alloy billets were fabricated by a powder metallurgy route, and their microstructure and mechanical properties were investigated. Rapidly solidified amorphous powders were produced by a conventional N 2 gas atomization method. In order to consolidate amorphous alloy billets, a spark plasma sintering (SPS) equipment was set up, and variables for hot consolidation were established. Using the consolidation temperature of 480 °C under a pressure of 80 MPa, good quality amorphous alloy billets having very few micropores or crystalline phase particles were obtained. Compressive strength of the billet was 1.8 GPa, which was about 6% lower than that of the cast amorphous alloy billet. This reduction was associated with the presence of few micropores, crystalline phase particles and thin oxide layers formed along prior powder boundaries in the billets. Amorphous matrix composite billets containing Cu particles homogeneously distributed in the amorphous matrix were successfully fabricated by the SPS consolidation. These composite billets showed a considerable amount of plastic strain because of the presence of ductile Cu particles, although their compressive strength was lower than that of the amorphous alloy billets.

Cu-based bulk amorphous alloys prepared by consolidation of amorphous powders in the supercooled liquid region

We report the fabrication of the Cu–Ni–Zr–Ti bulk amorphous alloys by warm rolling of amorphous powders, which have been prepared by a high-pressure gas atomization. The Cu 54Ni 6Zr 22Ti 18 amorphous powders obtained by a high-pressure He gas atomization method has a wide supercooled liquid region of 53 K. By warm rolling of amorphous powders in the supercooled liquid state, a fully amorphous Cu 54Ni 6Zr 22Ti 18 alloy is successfully synthesized. The conditions for rolling are obtained from the time–temperature–transformation curve by measuring the time for the onset of crystallization during isothermal annealing in differential scanning calorimetry. The rolled bulk amorphous Cu 54Ni 6Zr 22Ti 18 alloy exhibited high strength about 1.9 GPa, which is against similar to that obtained in the as-cast bulk amorphous alloy.

Vacuum hot pressing of gas-atomized Ni–Zr–Ti–Si–Sn amorphous powder

Fully amorphous Ni 57 Zr 20 Ti 18 Si 3 Sn 2 powders without any crystallinity are successfully fabricated in the particle size range below 75 μm by gas-atomization method. Gas-atomized Ni 57 Zr 20 Ti 18 Si 3 Sn 2 amorphous powder exhibits the glass transition temperature ( T g ) of 828 K and the crystallization temperature ( T x ) of 886 K. The gas-atomized Ni 57 Zr 20 Ti 18 Si 3 Sn 2 amorphous powder posesses a supercooled liquid region (Δ T x ) of 58 K. Based on the determined consolidation condition, the gas-atomized Ni 57 Zr 20 Ti 18 Si 3 Sn 2 amorphous powder was consolidated by a vacuum hot pressing apparatus. The optimum consolidation conditions were determined by isothermal annealing of Ni 57 Zr 20 Ti 18 Si 3 Sn 2 amorphous powder. The consolidated bulk Ni 57 Zr 20 Ti 18 Si 3 Sn 2 samples show completely amorphous on processing after consolidation. The relative density and hardness of the consolidated bulk Ni 57 Zr 20 Ti 18 Si 3 Sn 2 compacts are greater than 99 % and 800 Hv, respectively.

Development of Hydrogenating Powder Alloys for the Electrodes of Alkali Batteries. Part 3. Production Characteristics of Gas-Atomized Powders of Multicomponent Intermetallic Alloys

Alloy powders containing rare earth metals are prepared by the gas atomization method and their structure, surface, technological, and electrochemical properties are studied. Powders of the alloys LaNi4.5Al0.5, LaNi2.5Co2.4Al0.1, and (Mm, La)Ni3.5Co0.7Al0.35Mn0.4Zr0.05 are prepared with different particle sizes. The morphology, oxygen content and crystal structure of powders in relation to particle size are studied by x-ray analysis, electron microscopy, and surface dispersion spectroscopy. The hydrogen capacity and electrochemical properties of different fractions are determined. It is established that all of the fractions have similar morphology and alloy lattice parameters. The surface of gas atomized powders with less particle size is less contaminated with oxygen compared with larger fractions. At the same time fractions with a particle size <50 μm have poor activity during gas and electrochemical hydrogenation. DTA curves for fractions of fine particles have an additional exothermic peak that may be caused by thermally induced transformation of the amorphous component into crystalline. The coarse fraction of gas atomized powder has the same hydrogen and electrochemical capacity as for fuzzed alloys.