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Particulate matter (PM) emitted during laser additive manufacturing with stainless steel powder materials has been studied in detail. Three different additive manufacturing techniques were studied: selective laser melting, direct metal deposition and laser cladding. Gas flow and temperature fields accompanying the processes were numerically modeled for understanding particle growth and oxidation. Transmission and scanning electron microscopy were used for primary particle and PM characterization. The PM collected in the atmosphere during manufacturing consisted of complex aggregates/agglomerates with fractal-like geometries. The overwhelming number of particles formed in the three processes had equivalent projected area diameters within the 4–16 nm size range, with median sizes of 8.0, 9.4 and 11.2 nm. The primary particles were spherical in shape and consisted of oxides of the main steel alloying elements. Larger primary particles (> 30 nm) were not fully oxidized, but where characterized by a metallic core and an oxidic surface shell.

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The nature of vortices in the gas flow in atmospheric pressure ICPs is analyzed based on comparison of a Lorentz force exerted on the plasma and a gas inertia force. The theoretical analysis is supplemented by numerical modeling and experimental data. The theory is applied to explain a fundamental difference between spectroanalytical ICPs (SICPs), which are used as atomic and ionic sources for elemental analysis, and technological ICPs (TICPs) used for plasma processing of powders. It is shown that in the SICPs the pattern of the gas flow is predominantly determined by gas-dynamic effects. In the TICPs the vortices and the flow pattern are in contrast produced by the Lorentz force. The theory is also applied to find practical ways to reduce the effect of vortices in TICPs.