Arc plasma torches are the primary components of various industrial thermal plasma processes involving plasma spraying, metal cutting and welding, thermal plasma CVD, metal melting and remelting, waste treatment, and gas production. They are relatively simple devices whose operation implies intricate thermal, chemical, electrical, and fluid dynamics phenomena. Modeling may be used as a means to better understand the physical processes involved in their operation. This article presents an overview of the main aspects involved in the modeling of DC arc plasma torches: the mathematical models including thermodynamic and chemical nonequilibrium models, turbulent and radiative transport, thermodynamic and transport property calculation, boundary conditions, and arc reattachment models. It focuses on the conventional plasma torches used for plasma spraying that include a hot cathode and a nozzle anode.

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NiCrAlY layers containing different amounts of Al2O3 (0, 3, 6, 12, 18 wt.%) were deposited onto stainless steel substrates by a “hybrid” plasma spray process whereby the NiCrAlY powder was fed in dry form whilst fine Al2O3 powder, dispersed in ethanol, was injected through a suspension feeding system.\ud The Al2O3 reinforcement, consisting of fine, rounded particles interspersed within larger NiCrAlY lamellae, only causes marginal changes in hardness, due to the limited particles-matrix cohesion. Nonetheless, at room temperature, ball-on-disk dry sliding wear rates against sintered Al2O3 counterparts decrease from ≈5⁎10−4 mm3/(Nm) for pure NiCrAlY to ≈5⁎10−6 mm3/(Nm) with 18 wt.% Al2O3 addition. Pure NiCrAlY indeed suffers adhesive wear, whereas, on the composite coatings, the pull-out of some Al2O3 particles triggers the formation of a tribo-layer of smeared oxide fragments, which mediates the contact with the counterbody.\ud At 400 °C and at 700 °C, all wear rates are levelled to ≈8⁎10−5 mm3/(Nm) and ≈2⁎10−5 mm3/(Nm), respectively. An oxide layer grows on the NiCrAlY matrix upon high-temperature exposure, resulting in a tribo-oxidation wear mechanism, which makes the addition of Al2O3 irrelevant. At 700 °C, coatings are further strengthened by partial healing of interlamellar defects and by fine-grained β-NiAl precipitating within the metal matrix

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International audiencePlasma spraying using liquid feedstock makes it possible to produce thin coatings (<100 lm) with more refined microstructures than in conventional plasma spraying. However, the low density of the feedstock droplets makes them very sensitive to the instantaneous characteristics of the fluctuating plasma jet at the location where they are injected. In this study, the interactions between the fluctuating plasma jet and droplets are explored by using numerical simulations. The computations are based on a three-dimensional and time-dependent model of the plasma jet that couples the dynamic behaviour of the arc inside the torch and the plasma jet issuing from the plasma torch. The turbulence that develops in the jet flow issuing in air is modeled by a large Eddy simulation model that computes the largest structures of the flow which carry most of the energy and momentum

This study examines the fundamental reactions that occur in-flight during the solution precursor plasma\ud spraying (SPPS) of solutions containing Zr- and Y-based salts in water or ethanol solvent. The effect of\ud plasma jet composition (pure Ar, Ar-H 2 and Ar-He-H 2 mixtures) on the mechanical break-up and\ud thermal treatment of the solution, mechanically injected in the form of a liquid stream, was investigated.\ud Observation of the size evolution of the solution droplets in the plasma flow by means of a laser\ud shadowgraphy technique, showed that droplet break-up was more effective and solvent evaporation was\ud faster when the ethanol-based solution was injected into binary or ternary plasma gas mixtures. In\ud contrast with water-based solutions, residual liquid droplets were always detected at the substrate\ud location. The morphology and structure of the material deposited onto stainless steel substrates during\ud single-scan experiments were characterised by SEM, XRD and micro-Raman spectroscopy and were\ud shown to be closely related to in-flight droplet behaviour. In-flight pyrolysis and melting of the precursor\ud led to well-flattened splats, whereas residual liquid droplets at the substrate location turned into non\ud pyrolysed inclusions. The latter, although subsequently pyrolysed by the plasma heat during the depo-\ud sition of entire coatings, resulted in porous ‘‘sponge-like’’ structures in the deposit