Mise au point des moyens expérimentaux de détermination par diffraction des rayons X des contraintes au cours de l’oxydation des alliages métalliques à haute température

Installation of an experimental equipment for X ray diffraction study of residual stress during high temperature oxidation

¹ LM3, CNRS URA 1219, ENSAM.
² ISMA, Laboratoire de métallurgie structurale, CNRS URA 1107, Université Paris XI, Orsay.
³ Laboratoire de Recherche sur la Réactivité des Solides, CNRS LA 23, Faculté des Sciences de Mirandes, Dijon.

Abstract

The residual stresses in the oxide scale grown on alloys used at high temperature are of great importance in preventing the lifetime of the alloy. The sin² ψ method by means of X-ray diffraction represents some advantages, compared to the other methods, for its rapidity and its non destructivity. Most of the studies by X-ray diffraction were carried out at room temperature, which do not enable to distinguish the oxidation stresses, i.e. the stresses generated during the scale growth, from the thermal stresses, developed during cooling. In the aim of studying the evolution of the stresses during the oxidation treatments, a high temperature chamber of X-ray diffraction was developped and set up in the laboratory LM3-Ensam with a financial support from the Cefracor. The existing methods for studying the residual stresses and some results using X-ray diffraction are reviewed and discussed in the first part of this paper. The problems and difficulties encountered with the equipment are described later. Some first experiences with this apparatus are then discussed here : the stress relaxation in vacuum of a shot peened steel sample and the stress variation in a NiO scale were studied as a fonction of temperature.