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

An International Journal

ISSN for PRINT: 1093-3611

Institutional price:	$604.00
Issues per year:	4

Best Paper Award Selection - Editorial Board Site

2004, Volume8

168 pages

DOI: 10.1615/HighTempMatProc.v8.i2

Issue price - $144.00

ALUMINA-COATED STEEL: ROLE OF A MAGNETITE INTERPHASE ON THE ADHESION OF THE COATINGHT

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

A. Denoirjean
Science des Precedes Ceramique et de Traitement de Surface, University of Limoges, UMR CNRS 6638; France

R. Danoix
Laboratoire d'Analyse Spectroscopique et de Traitement de Surface des Materiaux - University of Rouen - Institut des Materiaux de Rouen; France

B. Lefez
Laboratoire d'Analyse Spectroscopique et de Traitement de Surface des Materiaux - University of Rouen - Institut des Materiaux de Rouen; France

B. Hannoyer
Laboratoire d'Analyse Spectroscopique et de Traitement de Surface des Materiaux - University of Rouen - Institut des Materiaux de Rouen; 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 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

ABSTRACT

To improve the adhesion of alumina coatings on low carbon steel, it is necessary to develop an oxide layer with a controlled thickness and chemistry at its surface. The best results were obtained with a wustite layer. The Wustite layer (Fe_1-xO) is developed on a smooth low carbon iron substrate by its oxidation within a furnace under a pure CO₂ atmosphere. However, before spraying, a preheating of the substrate and thus of its oxide surface by the plasma is mandatory in order to eliminate condensates and adsorbates. This step of the process induces more or less the transformation of wustite into magnetite (Fe₃O₄).
The purpose of this paper is the study of the influence of the magnetite phase and of the thickness of the oxide layer on the adhesion of Al₂O₃ coatings. The results show that the control of the oxide layer thickness is very important for a good adhesion which is probably linked to the cohesion of the layer. Below a critical thickness of the oxide layer the rapture of the coating is adhesive (at the interface alumina-iron oxide). Over it is a cohesive rupture inside the oxide layer. The composition of the oxide plays a role that is not still completely clarified, but the physico-chemical continuity of the phases present in the interfacial zone seems to be a crucial point.