High Temperature Material Processes (An International Quarterly of High-Technology Plasma Processes) An International Journal

ISSN for PRINT: 1093-3611

For Online Access

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2000, Volume4

Issue 3

152 pages

Issue price - $144.00

Helene Ageorges
SPCTS, UMR-CNRS 6638 University of Limoges, 123, avenue Albert Thomas, 87060 Limoges Cedex, France

Pierre Fauchais
Laboratoire Sciences des Precedes Ceramiques et de Traitements de Surface, UMR 6638 CNRS-Universite de Limoges, faculte des Sciences et Technique, conventionne avec le CEA n° M08, France

Investigations are carried out to study the oxidation of stainless steel particles collected after their flight in a plasma jet. In some tests, the injected particles are coated with an alumina shell. Particles are sprayed in Atmospheric Plasma Spraying (APS) and then collected in a concentric cylinder where they are quenched by argon jets. SEM observations of sprayed stainless steel particles show the formation of dark spots within their clear cross section, which displays the chromium and oxygen elements prominently. X-ray diffraction shows a chromium oxide phase which seems to be CrO. This is due to the convective movements within the particle renewing continuously fresh chromium at the surface and entraining the formed CrO inside the particle. It seems that, as for FeO, CrO is immiscible with liquid steel. On the other hand, alumina coated particles are less oxidized : cross sections present less oxide inclusions. Two types of particles were observed : some are still fully coated but the shell is broken due to the higher expansion of the stainless steel core. They probably result from particles where alumina has not been fully melted. Others have their alumina fused and entrained by liquid flow to the back of the moving droplet. Fused alumina droplets at the particles surface have coalesced creating a melted alumina cap. The two types of particles are probably due to the wide distribution trajectories within the spray cone which result in temperature differences. The particles with the alumina at the tail have probably traveled in the core of the plasma jet where temperatures are higher and then both materials have been melted, whereas the others have traveled in the jet fringes where the temperatures are lower.

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