Etude de la formation d'extrusions-intrusions et des structures de dislocations en fatigue dans le cuivre et le laiton 70cuivre-30zinc.

摘要

e have performed low-cycle fatigue tests on specimens of polycrystalline copper and ;We studied the evolution of the morphology of the surface relief as a function of the applied strain amplitude. The observations indicated that a low strain amplitude favoured the formation of thin extrusions-intrusions and a high strain amplitude favoured the formation of a hill-and-valley surface topography in both copper and 70Cu-30Zn. Some observations carried out on the partially-opened intrusion or microcracks indicated clearly that the thin extrusions had been produced by a mechanism of closure and of crack surfaces. We propose a mechanism to explain our observations. As well, we have compared our results and the proposed mechanism with the results obtained from the previous studies and furthermore we found that this proposed mechanism was compatible with the most important observations of the previous studies.;The characteristics of the hill-and-valley topography showed that the development of this relief has a different explanation than that for the development of thin extrusions-intrusions.;Surface relief morphology observations indicated that the characteristics of the reliefs produced by a cyclical deformation at R ;The structures of dislocations have also been studied on both fatigued copper and 70Cu-30Zn. On the fatigued copper specimens, we studied the formation of the vein structure and the distribution of the secondary dislocations in this structure. The transition of vein structure to the other dislocations structures were also studied. We paid attention to the role of the secondary dislocations on the formation of persistent slip bands (PSB's). Some aspects which indicate the sweeping of the dipolar loops at the early stage of the formation of PSB's and of other dislocations structures have been shown in this study. We have explained the different orientations of the dipolar loops structures using the mechanism proposed by Dickson et al.;The dislocations structures produced by cyclical deformation in the 70Cu-30Zn appear very complex. We showed the evolution of the dislocations structures as a function of the applied strain amplitude.;Finally, we showed the different aspects of the dislocations structures produced at R