In-Flight Oxidation of Stainless Steel Particles in Plasma Spraying

Autor: J.C. Labbe, Paule Denoirjean, A. A. Syed, Pierre Fauchais, Alain Denoirjean
Rok vydání: 2005
Předmět:
Zdroj: Journal of Thermal Spray Technology. 14:117-124
ISSN: 1059-9630
Popis: Air engulfment by the plasma jet in air plasma spraying (APS) causes in-flight oxidation of metallic particles. This oxidation, often complex and difficult to explain by classic diffusion-controlled oxidation, is governed by several mechanisms. This paper highlights the possible in-flight oxidation mechanisms in metallic particles with a focus on the convective oxidation. Two different types of austenitic stainless steel particles were air plasma sprayed using a direct current plasma gun and were collected in an argon atmosphere. Preliminary experiments indicated that different mechanisms are likely to occur during the in-flight oxidation of particles. The mass transfer from surface to interior of particle occurred, forming oxide nodules within particles. The mass transfer is governed by convective movements inside liquid particles within the plasma jet core due to the plasma-particle kinematic viscosity ratio greater than 50 and particle Reynolds number (Re) higher than 20. The nodules were composed of metastable phases consisting of mixed oxide of Fe and Cr. Convective movements within particles ceased roughly outside of the plasma jet core, and classic surface oxidation was found to be the dominant phenomenon forming the surface oxide layer. Moreover, the molten surface oxide outside the jet core may become entrained toward the tail of the particle if plasma conditions promote a higher particle Re number. The major oxide phase in collected particles was FeCr2O4, in a nonstoichiometric form of Fe3−x Cr x O4.
Databáze: OpenAIRE
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