Impact of hydrogen on the high cycle fatigue behaviour of Inconel 718 in asymmetric push–pull mode at room temperature. (January 2015) - Bruchhausen, M.
Highlights: We report HCF tests on Inconel 718 in gaseous hydrogen at asymmetric push–pull mode. Gaseous hydrogen (GH2) has a deleterious impact on the fatigue life time N f . The influence of GH2 on N f increases with decreasing mean or oscillating stress. An expression to calculate N f as a function of σ a and σ m is proposed. SEM micrographs of the fracture surfaces show signs of hydrogen embrittlement. Abstract: The influence of hydrogen on the high cycle fatigue (HCF) behaviour of Inconel 718 has been studied at room temperature in asymmetric push–pull mode using an ultrasonic HCF test rig. Fatigue tests have been carried out in gaseous hydrogen (GH2) and in Ar at a pressure of 30 MPa. Oscillating stresses with amplitudes ( σ a ) up to 450 MPa and mean stresses ( σ m ) up to 600 MPa have been applied. For a given σ a and σ m, the lifetime in Ar is generally longer than in GH2, which is explained by a hydrogen-induced embrittlement of the material. For a constant σ a of 218 MPa, the lifetime in Ar and in GH2 is very similar for high σ m, but the difference in lifetime increases as the mean stress decreases. An approach is presented to describe the number of cycles to failure N f as a function of σ a and σ m . Microstructural analysis has been performed on the specimens tested at σ a = 218 MPa and two values of σ m (300 MPa and 600 MPa). SEM analyses of the fracture surfaces of these samples indicate embrittlement of the material when tested in hydrogen atmosphere.