Comparaison de la résistance à l'oxydation à haute température des alliages MA 956 et Kanthal APM

Performances of MA 956 and kanthal APM alloys in high temperature and aggressive environment

Laboratoire de Métallurgie Structurale, ISMA, CNRS URA 1107, Université Paris-XI, Orsay

Abstract

The high temperature oxidation behaviour of two alumina former ferritic alloys -Kanthal APM and MA 956 - was studied in isothermal and cyclic conditions, in pure oxygen, air and industrial atmosphere. Under laboratory conditions (t < 15 days), in oxygen or in air, the MA 956 alloy seems more resistant to oxidation than the Kanthal APM, when, under industrial conditions, the Kanthal APM oxidation behaviour is better on account of the formation of a thin and compact alumina scale under the spalled zones. This is due to the fact that the aluminum depletion in the substrate is smaller for the Kanthal APM than for the MA 956.

This work was focused on the influence of materials in the vicinity of the tested samples on the oxidation process and on the role of a preliminary deformation of the samples :

- the alumina scale formed on these alloys is destabilized by the presence of any material which has a great affinity for Al. This is related to a gaseous Al transfert according to the reaction :

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This reaction enhances the aluminum depletion in the substrate. Inversely, the solution for avoiding such a transfert consists in putting in the vicinity of the tested samples a material enriched in alumina.

- the oxidation rate of curved samples is accelerated when compared to that of straight samples. This oxidation rate increase induces an enhancement of the Al depletion in the substrate.