Dislocation multiplication, vacancy accumulation, and the onset of jerky flow during forward and reverse 1 strain in Cu-3.2 at. % Sn

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Abstract
The theory of the Portevin—Le Chatelier effect is extended to include the effect of dislocation multiplication. The dislocation density ρ in Cu-3.2 at. % Sn is measured as a function of true plastic strain ε by the transmission electron microscopy of thin films, and the relation ρ= 4.73 × 1011 ε1.17 established. The effect of pre-strain and resting upon the onset of jerky flow is measured, and the relation cV ≃ 10−2 ε1.03 deduced for the increase in vacancy concentration. The vacancy lifetime appears to be of the order of minutes at 140°c. During reversed strain, it appears that the dislocation density at first decreases, and then increases again according to the above relation. Reversed strain does not create vacancies at a rate greater than unidirectional deformation.