Spherical particles with and without attached nanoparticles formed by DC-arc spheroidization of irregularly shaped stainless-steel powder

Abstract

Water-atomized powder of SUS316L stainless steel was spheroidized by DC arc plasma to obtain a spherical powder with high fluidity and high packing density at low cost. This process successfully spheroidized the raw powder and improved the powder characteristics. In the spheroidized powder, fluidity was enhanced by up to 100% versus raw powder; tapped density was likewise increased by up to 50% versus raw powder. We also formed a nanoparticle-modified spherical powder. Spark plasma sintering using spheroidized powders yielded high densities, including a relative density of 99.6% for the compact produced from nanoparticle-modified powder.

Thermal Plasma Spheroidization and Characterization of Stainless Steel Powders Using Direct Current Plasma Technology

“…This evidence can be explained considering that, during the process, the injected particles absorb energy from the plasma, and if the energy is enough, they melt; once out of the plume, the particles start to cool down, and due to the action of surface tension forces, their shape becomes spherical. If the absorbed energy exceeds that required for melting, the particles evaporate; in this case the rapid quenching of the reactor determines their recondensation in the form of nanoparticles [17].…”

“…Indeed, there are few scientific papers on the production of spherical particles using DC plasma in the literature, particularly for metals [12][13][14][15][16]. Itagaki et al [17] had a good degree of spheroidization in SS316L steel (commercial powder with irregular shape, average diameter 38 microns, obtained by water atomization) with experimental tests using DC plasma between 9 and 17 kW. A good spherical powder (>80%) was already obtained at 9 kW, even if higher powers were needed to treat the powder fraction with a diameter larger than 50 µm.…”

Thermal Plasma Spheroidization and Characterization of Stainless Steel Powders Using DC Plasma Technology

“…The tests show that the average circularity value is always higher than 0.8, indicating an extensive spheroidization of the powders, whatever the raw powder processed. Itagaki et al [17] also obtained powders with high sphericity and uniform size distribution by performing a DC arc plasma spheroidization under appropriate processing conditions, but nanoparticle-modi ed spherical particles were obtained already at 17 kW starting from raw powder of averaged diameter of 38 µm. In our conditions, the spheroidization process was conducted on two set of commercial powders of wider averaged diameter (till to 149 µm) with encouraging results both in terms of sphericity and nanoparticles formation; furthermore, these results are particularly representative due to the relevant dimensions of our experimental set-up, which could be easily scaled up.…”

“…These new DC systems therefore appear interesting due to their high energy e ciency and can be used for the realization of high temperature processes on an industrial scale.Indeed, there are few scienti c papers on the production of spherical particles by DC plasma in the literature, particularly for metals [12][13][14][15][16]. H. Itagaki et al [17] had a good degree of spheroidization of SUS316L steel (commercial powder in irregular shape, average diameter 38 micron, obtained by water atomization) with experimental tests between 9 and 17 kW by DC plasma. A good spherical powder (> 80%) was already obtained about 9 kW, even if higher powers were needed to treat the powder fraction with a diameter larger than 50 µm.…”

DC Arc Plasma Treatment for Defect Reduction in WC-Co Granulated Powder

“…In order to obtain a WC agglomerated powder without the internal gaps that generate porosity in resulting AM products, we have proposed a direct current (DC) arc plasma treatment for a powder of WC with Co binder. In our previous study using DC arc plasma processing, we succeeded in spheroidizing an irregularly shaped stainless powder and in reducing internal defects of the stainless steel powder [9]. In this technique, the powder can be heated in a high-temperature plasma in a short time, for a powder-plasma total exposure time of a few milliseconds.…”