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Progress in Plasma Processing of Materials, 2003

ISBN:
978-1-56700-192-1 (Print)
978-1-56700-447-2 (Online)

INFLUENCE OF DC PLASMA PREHEATING ON OXIDE LAYERS FORMED BY FURNACE HEATING ON LOW CARBON STEEL SUBSTRATES AND RESULTING ADHESION/COHESION OF ALUMINA COATINGS

S. Valette
SPCTS - Science des precedes Ceramique et de Traitements de Surface - UMR CNRS 6638 - University of Limoges -123 Avenue Albert Thomas - 87060 Limoges Cedex - France

Alain Denoirjean
Equipe Plasma Laser Matériaux, ESA CNRS 6015, 87060 Limoges Cedex, France

Pierre Lefort
Laboratoire Science des Precedes Ceramiques et Traitements de Surface UMR CNRS 6638 123 Avenue Albert-Thomas F-87060 Limoges Cedex, France

Pierre Fauchais
Laboratoire Sciences des Procedes Ceramiques et de Traitements de Surface UMR CNRS 6638 University of Limoges 123 avenue Albert Thomas, 87060 LIMOGES - France

Abstract

In plasma spraying the preheating of low carbon steel substrates (X40) with a rough surface resulting from grit blasting, has received an increased interest because it promotes the adhesion and cohesion (A/C) of alumina coatings. Earlier works have reported the generation of a duplex Fe3O4/Fe2O3 layer after preheating by the d.c. plasma jet. Improved A/C values were obtained for an increase in Fe3O4 content in the oxide layer. Much improved adherence values were achieved with alumina spayed on Fel-xO layers. In this case, the Adhesion/cohesion values obtained on smooth substrate (Ra ~ 0.1 µm) were good (~ 40 MPa) and close to those obtained on rough ones (Ra ~ 5 µm). First the time evolution of the Fel-xO layer thickness and morphology produced in a controlled atmosphere furnace was studied. Then the influence of the plasma preheating of the wustite layers was studied by SEM, and XRD analyses. XRD analysis results indicated a slight variation in the oxide phases depending on the preheating cycles. Fe3O4 was found to increase when a decomposition of Fel-xO into Fe3O4 was observed.