Study of dislocation dynamics of copper single crystals under cycling loading through acoustic emission and microstructural characterizations

During plastic deformation of crystalline materials, a soft plasticity, made of numerous uncorrelated dislocation movements coexists with a wilder plasticity, in the form of collaborative movements: dislocation avalanches. The coexistence of the two plasticities depends on the establishment of a dislocation structure, which is supposed to hinder the propagation of avalanches. We propose to study the correlation between the microstructural evolution of the dislocation arrangements and the nature of the dislocation dynamics, during cyclic loading of pure copper single crystals. Different fatigue tests with imposed stress amplitude are performed to study the influence of (i) the loading path, (ii) the loading ratio and (iii) the crystallographic orientation on the plasticity phenomena. The acoustic emission (AE) technique is used to study both types of plasticity : the continuous AE is associated with soft plasticity and the discrete AE with wild plasticity. The dislocation microstructures are studied using EBSD (crystal disorientation) and ECCI (Electron Channeling Contrast Imaging) techniques at the end of each fatigue stage. The AE-ECCI coupling gives valuable information about the dislocation dynamics of dislocations. This study shows a certain universality, with (i) the existence of dislocation avalanches, produced during a more or less deep reorganization of the structures, (ii) a progressive evolution, during the cycles, of the dislocation mean free path, associated with the emergence of a dislocation structure and (iii) an inhibition of avalanches during the emergence of a dislocation arrangement. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg