Revealing the influential mechanism of strain ranges on cyclic-life saturation during creep-fatigue in Nickel-based superalloy DZ445

Abstract

The creep-fatigue interaction has been recognized as the main failure mode of most structural components operating in the high-temperature regime. The cyclic life (Nf) usually decreases continuously with the dwell time in their interactions. However, Nf shows an abnormal change, i.e. keeps constant or slightly increases/decreases, in the present studied Nickel-based superalloy, DZ445. This means that generalized “Nf saturation” is achieved by a dynamic equilibrium between the straight single superdislocations and dislocation networks corresponding to local and homogeneous damage, respectively. The saturation appears more easily with the increasing high strain ranges. The variation in the mechanical response parameters, the damage characterizations, and the phase involutions with the increasing dwell time exhibits the low amplitude under the high strain range. The combined characteristics show that the easy occurrence of Nf saturation in the range of large deformations is obtained by increasing the local-damage. The low change rate of straight single superdislocations with the dwell time in the range of large deformation is well confirmed by the above mechanism. The parameters in the different criterion models of the cyclic-life “saturation phenomenon” unify the mechanical response and the damage mechanism soundly. The work provides a new theoretical basis and guidance for the creep-fatigue safety design of high-temperature metallic materials and the establishment of dislocation-based models.