II - Endommagement à haute température d’un superalliage monocristallin AM1

Environment effects at high temperature on fatigue damage of the <001> single crystal superalloy AM1

Abstract

In order to improve the efficiency of gas turbine for jet engines, motorists employ materials which must respond to severe demands at high temperature. Among them, the superalloys obtained by using directional solidification present the best high temperature capability. Such superalloys still have small micro- structural defects The Ni-base AMI used for the manufacturing of blades is one of them. It is covered with a Cr-NiAl coating so as to ensure protection against oxydo-corrosion .

The aim of this study is to assess the experimental importance of creep, fatigue and oxydation on damage mechanisms at 950°C on coated AMI. Notably, we study the initiation and the propagation processes in relation with microstructural defects or the deposit, and the influence of environment on these. For that, fatigue tests are made on coated and uncoated specimens at 950°C in vacuum as well as in the air of the laboratory.

For all specimens, fatigue tests performed in vacuum revealed far less damage than those performed in air. In spite of this, for the stress levels applied until now, we did not observed any influence on fatigue lives but only on crack initiation. In particular, the deposit seems to play a different role on crack initiation according to the environment conditions of testing.