Latent hardening effects in low cycle fatigue of copper single crystals

Latent hardening produced by different dislocation patterns in fatigued copper single crystals and the stability of these structures under the change of dominant slip mechanism have been studied under conditions of secondary fatigue at room temperature. Due to the larger anisotropy of the dislocation substructure, easy glide orientations of single crystals produce stronger latent hardening in non-coplanar slip systems than multiple slip orientations. There is no correlation between latent hardening ratios for different slip systems and the fatigue behavior of the secondary samples. The secondary samples may exhibit hardening or softening, depending on the relation between saturation stress of the secondary samples and the latent hardening produced by the primary substructure in the latent slip systems. The pre-saturation region in single crystals is strongly dependent on the pre-existing dislocation substructure and the slip systems operating during secondary fatigue. The saturation stress is independent of the fatigue history and the microstructure and is controlled by the crystallographic orientation of the samples and the scale of the dislocation pattern developed at saturation.