COMPARISON OF STAINLESS STEEL-ALUMINA COATINGS PLASMA SPRAYED IN AIR BY TWO DIFFERENT TECHNIQUES

P. Denoirjean*, A. A. Syed, R. Cuenca-Alvarez,

A. Denoirjean, H. Ageorges, J. C. Labbe, P. Fauchais

University of Limoges - Sciences des Procédés Céramiques et Traitements de Surface,

CNRS UMR 6638 , 123 avenue Albert Thomas, 87060 Limoges Cedex, France

* Corresponding author. E-mail: alain.denoirjean@unilim.fr

Received : 15 February 2003; revised version accepted : 09 June 2004

Abstract

316L Stainless steel-alumina coatings were plasma sprayed in air by two different techniques. The first one was achieved by co-spraying of the metallic and ceramic powders, whereas the second one by spraying of a composite powder. This composite powder was produced by mechanofusion resulting in particles with stainless steel core coated by an alumina shell. Splat morphology, coating microstructures and micro hardness were studied.

Splats were collected using both techniques on non preheated and 300°C preheated substrates of plain carbon steel. During their flight in the plsam jet, the co-sprayed particles behave independently forming splats identical to that resulting of individual particles whereas mechanofused particles lead to hybrid splats composed of metallic and ceramic materials, whith alumina impacting exactly on the steel splats. Mechanofused powder, therefore, results in finer coating microstructure and shows alumina, uniformly distributed within the structure. Alumina shell also hinders at least partially in-flight oxidation of metallic phase that occurs due to the air entrainment inside the plasma jet. Cermet coatings developed by co-spraying, in contrast, exhibit higher oxide content resulting from in-flight oxidation of stainless steel powders, what explains that the highest hardness (510 ± 57 HV5) is obtained for co-spraying.

Keywords : Air Plasma Spraying; Cermet; Co-spraying; Mechanofusion; Stainless steel; Alumina.

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