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The high temperatures and stresses experienced within turbine discs require high temperature resistant Ni-base superalloys produced by Powder Metallurgy techniques. The alloy N18 we study has good overall mechanical properties at temperatures up to 700°C after appropriate heat treatment. These properties are derived from the precipitation of ordered y' phase and are strongly dependent upon the microstructure produced during thermal treatments. The y' precipitation kinetics is experimentally studied by dilatometry and transmission electron microscopy. The microstructural evolution of y' precipitates during quenching is followed in a high quenching rate apparatus that permits to preserve the high temperature microstructure at room temperature. In the present work, a model is being developped and is experimentally verified in order to describe the intragranular y' precipitation during quenching.

Cet article présente des exemples de résultats expérimentaux obtenus en diffusion de neutrons aux petits angles pour trois types de matériaux (alliages modèles FeCu, aciers austéno-femtiques inoxydables et superalliages à base nickel) différemment vieillis. Un modèle simple, différent dans chaque cas, permet de bien rendre compte des résultats expérimentaux et de déduire un certain nombre de paramètres intervenant dans la modélisation du vieillissement.

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