Plasma Spheroidization Research Articles

Simulation of the effect of evaporation and gas composition during plasma spheroidization of titanium particles

A 3D model was proposed that describes the in-flight behavior of titanium particles in the plasma environment, developed in the commercial CFD Ansys Fluent software, which described the heating of particles. The rate of evaporation was investigated based on the gas compositions, and the mass evaporated on the surface of the particle along the trajectory under plasma conditions. To evaluate the spheroidization rate of titanium particles, the calculated temperature and flow histories were established. Significant heat exchange behaviors are presented due to the variations in hydrogen content and feed rate. The simulation results have demonstrated that the range of 0-4% of H2 and at a low injection feed rate of 3-10 g/min minimized the evaporation rate and increased the spheroidization rate of particles.

Fabrication of spherical Ti-6Al-4V powder by RF plasma spheroidization combined with mechanical alloying and spray granulation

Spherical Ti-6Al-4V powder was produced by RF plasma spheroidization combined with mechanical alloying and spray granulation. Particle size distribution, morphology, specific surface area, apparent density, flowability, element distribution and content of alloy powders after each stage during the process were investigated. Results show that the obtained spheroidized Ti-6Al-4V alloy powder has dense structure, good sphericity and high spheroidization ratio (98%), moderate particle size (37.8 μm) with narrow distribution. It also has excellent flowability (33.2 s· (50 g)-1) and apparent density (2.53 g·cm−3). In addition, elements distribution in the spherical Ti-6Al-4V alloy powder is uniform and most of elements content of it is within the standard of Ti-6Al-4V alloy.

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.

Tribological and corrosion behavior of HVAF-sprayed (Fe-TiB2)/CNT composite coating

Fe-based composite coating doped well-dispersed titanium boride (TiB2) and carbon nanotubes (CNTs) was fabricated via combined ball milling, spray drying, plasma spheroidization and high velocity air fuel (HVAF) spraying. The microstructure evolution of composite powders and coating, the tribological and corrosion behavior of Fe-based metallic, Fe-TiB2 cermet and (Fe-TiB2)/CNT composite coatings were investigated. The results show that doping 50 vol. % TiB2, especially further doping 2.5 vol. % CNTs could remarkably render the coating favorable microstructure with low porosity, enhanced hardness and fracture toughness, and superior wear and corrosion resistance. Mild oxidative and slight abrasive wears were the dominant wear mechanism, and the preferential corrosion was occurred at the pores, inter-splats and then the TiB2-Fe interfaces.

Effect of powder loading on plasma spheroidization of hydride-dehydride titanium powders

Spherical titanium particles have been produced from hydride-dehydride titanium raw powders using an inductively coupled plasma spray system. Taking into account the variously modified particle morphologies with different plasma conditions, the effect of powder loading on spheroidization was quantified and evaluated in terms of the altered particle heating capabilities. The averaged particle heat transfer coefficient was found to vary with powder feeding rate and associated strongly with Ar–H2 gas thermal conductivity. Furthermore, there observed a most efficient particle heating condition for each powder feeding rate, but the efficient heating condition tends to vaporize small raw powders and increase the overall oxygen content unintentionally as a result of the attachment of satellites nanoparticles on spherical particles. It is therefore important that the plasma input power is optimally controlled with particular attention to the altered degree of heat transfer especially for the case of small powder injection.

Structure Evolution of Ni36Al27Co37 Alloy in the Process of Mechanical Alloying and Plasma Spheroidization

In this paper, a novel approach to obtain a ferromagnetic material for smart applications was implied. A combination of mechanical alloying (MA) and plasma spheroidization (PS) was applied to produce Ni36Al27Co37 spherical powder. Then its structure was systematically studied. It was shown that homogenization of the structure occurs due to mechanism of layered structure formation. The dependence of the lamella thickness on the energy dose input at MA was defined. It was found that 14.7 W⋅h/g is sufficient to obtain lamella thickness of 1 μm and less. The low-energy mode of a planetary mill with rotation speeds of the main disk/bowl of 150/−300 rpm makes it possible to achieve a uniform element distribution upon a minimal amount of impurity. During MA in an attritor Ni3Al-type intermetallic compounds are formed that result in more intensive degradation in particle size. Plasma spheroidization of the powder after MA allowed obtaining Ni36Al27Co37 spherical powder. The powder had a fine β + γ-structure. The particle size distribution remains almost unchanged compared to the MA stage. Coercivity of the powder is 79 Oe. The powder obtained meets the requirements of selective laser melting technology, but also can be utilized as a functional filler in various magnetic composites.

Preparation, mechanical properties and enhanced wear resistance of TiC-Fe composite cermet coating

TiC-Fe based cermet coating with high hardness and superior wear resistance together with low price and environmental friendliness was developed. Initially, the TiC-Fe composite particles were prepared by high energy ball milling, spray drying and plasma spheroidization. These cermet powders not only showed high sphericity and dense microstructure but also presented homogeneous distribution of TiC. Then, the TiC-Fe cermet coating was deposited by high velocity air fuel (HVAF). The results indicated that introducing ceramics would increase the deformation degree of the splats and eliminate the layered structure, which effectively enhanced the microhardness and wear resistance of composite coating. Compared with pure metallic coating, the microhardness of cermet coating increased to 887.5 HV0.3, while the wear rates of cermet coating reduced by 40% and 60% at 10 N and 25 N, respectively. Besides, the TiC-Fe cermet coating showed much less sensitive to the heavy load. The primary wear mechanism of single 316 L coating was a combination of adhesive wear and severe oxidation, while the TiC-Fe cermet coating showed slight abrasive wear combined with oxidation. The excellent wear resistance together with its harmless to human body make the TiC-Fe based composite coating a potential candidate when using at kitchen ware surface.

Plasma spheroidized MoNbTaTiZr high entropy alloy showing improved plasticity

Refinement of the harder phase in two-phase MoNbTaTiZr high-entropy alloys (HEA) prepared by a powder metallurgy route has enhanced strength and plasticity of the alloy. The MoNbTaTiZr HEA powder used in this study was prepared by hydrogenation–dehydrogenation followed by plasma spheroidization, having an inherent dual-phase structure (bcc1 and bcc2) similar to the arc melted alloy of the same composition but with much finer morphology of the bcc2 phase. The homogenous and fine distribution of the harder Zr-rich phase (bcc2) with ~10% volume fraction embedded inside the Ta-rich phase (bcc1) evaded the strength–ductility trade-off. The shear-band delocalization in the bcc1 matrix phase improved the strength as well as the plasticity of the alloy. The alloy has potential in biomedical implants because it shows excellent corrosion resistance and lower magnetic susceptibility, making it an MRI (magnetic resonance imaging)-friendly alloy.

Microstructure and mechanical properties of the ZrB2–SiC eutectic phase obtained via induction plasma spheroidization

The microstructure, phase composition and interfaces of ZrB2-30 vol%SiC eutectic were investigated using TEM fabricated via induction plasma spheroidization(IPS). The obtained ZrB2–SiC hypereutectic consists of the alternating H–ZrB2 and 6H–SiC lamellas, and its composition is ZrB2-65.04 mol.%SiC. 3 types of interfaces including SiC lamella-ZrB2 granule, ZrB2 lamella-SiC lamella and ZrB2 lamella-ZrB2 granule present a preferential orientation relationship. High-resolution TEM observations show that the ZrB2 phase in the eutectic prefers to growth along the (101) plane. In addition, the mechanical properties of each phase in the IPS-treated ZrB2–SiC powder were measured by nanoindentation. Hardness and elastic modulus of ZrB2 granules were measured 17.86 GPa and 168.97 GPa, respectively, while these values were obtained 9.99 GPa and 120.66 GPa for ZrB2–SiC eutectic phase.

A comparative study on spheroidization of sodium reduced and hydrogenation-dehydrogenation tantalum powder by RF plasma

Sodium reduced tantalum powder and hydrogenation-dehydrogenation tantalum powder were spheroidized by RF plasma, respectively. Influences of carrier gas flow rate, powder feeding rate and secondary spheroidization on particle size and morphology of the spheroidized tantalum powders were investigated. Results show that hydrogenation-dehydrogenation tantalum powder is more appropriate for radio frequency plasma spheroidization than sodium reduced tantalum powder. Spheroidization ratio, powder collection ratio and average particle size of the spheroidized tantalum powder all decrease as the carrier gas flow rate increases. Powder collection ratio and particle size decrease with the decrease of the powder feeding rate. Moreover, spheroidization ratio, flowability and apparent density of the spheroidized tantalum powder increases after secondary spheroidization process while particle size of it decreases.

Spheroidisation of Stainless Steel Powder for Additive Manufacturing

In additive manufacturing, powder characteristics play an important role in terms of flowability and densification, which can be improved by the use of spherical powders. In this study, irregular powder was spheroidised by plasma treatment, and the powder properties were measured. Powder characterisation was conducted to determine the morphology, particle size and distribution as well as the flowability. Spherical AISI 304 stainless steel powders were produced by plasma spheroidization, and the efficiency of the spheroidisation process was evaluated. The spheroidisation process resulted in 93% efficiency with a decrease of fine particles (<63 µm) by 22%, while the all the flowability parameters of the powder improved significantly.

Reactive plasma spraying of supersaturated tungsten super-hard Ta-Hf-W-C solid solution coating

A supersaturated tungsten Ta-Hf-W-C solid solution coating is successfully prepared by a reactive plasma spraying. The reaction process and solution behavior of TaC-HfC-WC-C composite powder during induction plasma spheroidization (IPS) and vacuum plasma spraying (VPS) are described. Compared with the direct spraying, the coating made by IPS-VPS multi-stage plasma heating process has lower porosity and better composition uniformity. The highest hardness obtained by nanoindentation can reach up to 43.3 GPa due to solid solution strengthening. This work provides a new method and a potential material for thermal spraying super-hard coatings.

Characterization of Ti6Al4V powders produced by different methods for selective laser melting

A comparative investigation was made into Ti6Al4V powders produced by electrode induction melting gas atomization (EIGA), plasma spheroidization (PS), and plasma atomization (PA) in terms of particle size distribution, shape, element distribution, microstructure, flowability and forming properties. The powders were characterized by a laser particle size and shape analyzer, a scanning electron microscopy (SEM), an energy dispersive spectrometer (EDS), an x-ray diffraction (XRD), a Hall-flow meter and SLM machine, respectively. Image analysis was used to quantitatively analyze the elongation and roundness of these Ti6Al4V powders. The results indicate that PA produces the smoothest powder with the lowest satellite sphere. The microstructure of the powders is composed of HCP-α‘ phase. The average elongation and roundness of EIGA Ti6Al4V powder is similar to those of PA Ti6Al4V powder. The flowability of the PA powder (26.23 s/50 g) is better than that of EIGA powder (32.16 s/50 g) and PS powder (35.30 s/50 g). The SLM Ti6Al4V samples produced by EIGA powder exhibit a well-balanced combination of strength (1047 MPa) and ductility (16.2%). In regard to the process of SLM, the PA and EIGA Ti6Al4V powders are more suitable than PS Ti6Al4V powder. The EIGA method is found to be the best choice among these three methods on account of cost and performance.

Preparation of Ni–Ti composite powder using radio frequency plasma spheroidization and its laser powder bed fusion densification

In this study, spherical Ni–Ti composite powder was synthesized from blended elemental Ni and Ti powders using radio frequency plasma spheroidization process. The effects of powder feeding rate and carrier gas flow rate on the spheroidization efficiency and Ni content of the obtained powders were investigated. The spherical Ni–Ti composite powder with a slightly Ti-rich composition was obtained at the optimal feeding rate of 35 g/min and carrier gas flow rate of 3 L/min. In addition to NiTi phase, elemental Ni and Ti powders were also identified in the produced powder. The prepared powder was adopted for laser powder bed fusion densification. Microcracks and pores were observed in the L-PBF-processed samples. In addition to NiTi main phase, un-melted elemental powders, Ti2Ni and Ni3Ti phases were found in the microstructure of the printed parts. Based on the DSC analysis, the transformation temperatures of austenitic NiTi to martensite and vice versa were determined.

Preparation of spherical Ti-6Al-4V powder by RF induction plasma spheroidization combined with spray granulation

Spray granulation was used to control morphology and particle size of raw materials for spheroidization in this work. Effects of dispersant (PAA-NH4OH) addition, pH value and solid content on stability of slurry for granulation was investigated. Influence of solid content of the slurry and atomizer speed on spray granulation were also investigated. Furthermore, difference in spheroidization effect between Ti-6Al-4V powder spheroidized from the granulated powder and irregular powder was compared. Results show that zeta potential of the slurry can be controlled at -44 mV to by addition of dispersant when pH value is 9.3. Granulated powder prepared with 50 wt% solid content and 10,000 rpm atomizer speed was best for plasma spheroidization. Ti-6Al-4V powder spheroidized from the granulated powder has better properties than that spheroidized from irregular powder. Spheroidization ratio, flow properties and apparent density of the spheroidized Ti-6Al-4V powder from granulated powder are 98%, 35.4 g/50s and 3.2 g/cm3, respectively.

Reactive Plasma Spraying of Super-Hard Ta-Hf-W-C Single-Phase Solid Solution Coating

A W supersaturated Ta-Hf-W-C single-phase solid solution coating is successfully prepared by a reactive plasma spraying. The reaction process of TaC-HfC-WC-C composite powder during induction plasma spheroidization (IPS) and vacuum plasma spraying (VPS) are described. Compared with the direct spraying, the coating made by IPS-VPS multi-stage plasma heating process has better density and composition uniformity. The highest hardness obtained by nanoindentation can reach up to 43.3 GPa due to solid solution strengthening. The lattice distortion induced by W solute atoms increases the resistance of dislocation movement, thus further improving the hardness of Ta-Hf-W-C solid solution coating. This work provides a new method and a potential material for thermal spraying super-hard coatings.

High-quality spherical zirconium alloy powders prepared by thermal plasma treatment for additive manufacturing

Spherical zirconium alloy (Zr-4) powders produced by thermal plasma spheroidization show great potential for additive manufacturing in the nuclear industry. After plasma treatment, high-sphericity (>0.95) powders with a narrower distribution and lower impurity element contents have been obtained. The spheroidized powders with a uniform particle distribution of 40 ~ 80 μm have been determined and exhibits a dense structure with good surface finish. Meanwhile, no element segregation is detectable after quick solidification of the alloy powders. The XRD patterns indicate that residual hydride phases have been substantially removed after spheroidization, significantly improving their purity. Furthermore, the content of oxygen and hydrogen has been decreased by ~ 34.9% (from 0.43 wt.% to 0.28 wt.%) and ~ 88.0% (from 0.92 wt.% to 0.09 wt.%), respectively, compared to the raw alloy powders. The effective and scalable strategy for fabricating spherical zirconium alloy powders may potentially broaden the application of metal zirconium for additive manufacturing.

Microstructure and mechanical properties of ultra-hard spherical refractory high-entropy alloy powders fabricated by plasma spheroidization

Spherical NbMoTaW high entropy alloy (HEA) powders with a uniform particle size distribution (d50 = 35.0 μm) were successfully prepared by using a novel industrial method combining spray drying and plasma spheroidization. The HEA powder presents an overall single body-centered-cubic structure, yet with cellular elemental segregation mainly involving Nb and W at the nanometer-scale. The microhardness of the HEA powder is 10.09 GPa, about 50% higher than that of the HEA with the same composition in bulk state. This ultra-high microhardness endows the HEA powder with potential for application as superhard materials. In addition, the new preparation method of spherical refractory HEAs powder also would be of great significance for the future development of refractory HEAs (or complex refractory alloys) towards industrial applications, especially those based on 3D printing and thermal coatings.

In situ synthesis of spherical W[sbnd]Mo alloy powder for additive manufacturing by spray granulation combined with thermal plasma spheroidization

In the present research, spherical WMo alloy powder for additive manufacturing was successfully synthesized by spray granulation (SG) in combination with thermal plasma spheroidization (TPS). Firstly, W and Mo particles (1–3 μm) were banded together through SG and formed porous agglomerated powder with desired particle size distribution and flowability. The porous agglomerated WMo powder was subsequently melted through thermal plasma, W and Mo dissolved together and formed solid solution accompanied with powder densification during TPS. Through optimization of the process conditions, the spheroidized WMo alloy powder exhibits homogeneous element distribution, low oxygen content (~0.08%), and good flowability (10 s/50 g), which meet the demand for laser powder bed fusion (LPBF). Remarkably, nearly full dense WMo alloy with few pores could be fabricated by LPBF based on the spheroidized WMo alloy powder.

Simulation Study of Smoothed Particle Hydrodynamics (SPH) Method in Plasma Spheroidization of W-Ni-Fe Ternary Alloys

Simulation Study of Smoothed Particle Hydrodynamics (SPH) Method in Plasma Spheroidization of W-Ni-Fe Ternary Alloys