I - Fissuration d’un superalliage base Nickel à 650°C sous air : effet de l’oxydation

Cracking resistance of a Ni based superalloy at 650°C under air environment: oxidation effect

Abstract

Creep-fatigue cracking resistance of alloy N18 has been studied at high temperature under air or vacuum conditions. Two microstructures with different creep resistance were used. It is shown that under air environment, the microstructure can influence the fatigue cracking resistance of this alloy. However, this effect disappears under vacuum conditions. Consequently, the local interaction between the mechanical behavior of the material and oxidation processes at the crack tip has been investigated. Specific creep-fatigue tests with forced relaxation have been carried out under air.

Concurrently, the oxygen partial pressure were cycled during the hold time of a creep-fatigue mechanical test.

From these different tests, it is concluded that the detrimental interaction between the environment and the local mechanical behaviour at the crack tip occurs during the first stages of the relaxation process taking place at the crack tip surface.