A local approach to creep-fatigue-oxidation interactions in Inco 718 alloy

André Pineau (1) , Raul de Moura Pinho (2) , Stéphane Pierret (2) , Caroline Mary (2)

1 CDM - Centre des Matériaux
2 SNECMA Villaroche [Moissy-Cramayel]

Understanding and modeling hold time effects on fatigue crack growth rate (FCGR) above 500 °C in Inco 718DA is a great challenge. Fatigue tests with a trapezoidal wave shape signal including hold times from 90 s to 3600 s were carried out on Inco 718DA with a small grain size (5-15 μm) over a wide range of temperatures (500 °C-650 °C). FCGRs were measured using potential drop technique. SEM observations were carried out to correlate the measured FCGRs with the trans- or inter-granular aspect of the fatigue fracture surfaces. Two regimes must be distinguished. The first regime associated with relatively short hold times can be represented by a power law, where da/dN is proportional to tα, α ~ 0.25. This first regime corresponds to the situation where the fatigue crack does not propagate during the hold time but its propagation takes place during the cyclic part of the loading over a damaged zone ahead of the crack tip. The second regime associated with longer hold times corresponds to the case where crack propagation during hold time (creep crack growth) is predominant. This regime is purely time dependent. Simple models are introduced to describe both regimes.

Mots clés: Inco 718; High temperature fatigue; hold time effect; fatigue crack growth

Domaines: Matériaux

André Pineau, Raul de Moura Pinho, Stéphane Pierret, Caroline Mary. A local approach to creep-fatigue-oxidation interactions in Inco 718 alloy. 13th international conference on fracture, Jun 2013, Beijing, China. 11 p. ⟨hal-00853420⟩