Effect of the environment on the high temperature embrittlement of inconel 718

Abstract The oxygen embrittlement of Inconel 718 has been investigated by means of hot tensile tests in an ultrahigh vacuum device. It has been shown that a pre-oxidizing treatment (200 h at 923 K) does not induce a major effect on the further mechanical behaviour of tensile samples when tested at 923 K in ultrahigh vacuum. In addition, a transition of the failure mode has been determined for an O 2 pressure as low as 10 −1 Pa. Possible interactions between external oxygen and internal hydrogen dissolved in the alloy have also been studied using hot tensile tests on either hydrogen-charged or hydrogen-degassed samples. Both types of sample exhibit the same mecahnical behaviour. Hot tensile tests under pure CO have also been carried out. The results obtained seem to indicate that the first stage of the oxidation process in the grain boundaries before Cr 2 O 3 formation plays an important role in the embrittlement mechanism of this alloy.