TEM study of the dislocation structure at the transition from discontinuous to viscous glide in Cu–Al and Cu–Mn alloys at elevated temperatures

Abstract

The dislocation structures developed during plastic deformation in the regimes of discontinuous glide (Portevin-Le-Chatelier effect, PLC) as well as viscous glide at elevated temperatures (600-800 K) have been studied by transmission electron microscopy in polycrystals of Cu-5Al, Cu-10Al, Cu-15Al and Cu-4.1Mn alloys (at.%). Discontinuous glide is characterized by correlated dislocation movement in few active slip planes due to breakaway of aged and rapid multiplication of fresh dislocations, while beyond the transition, when solute diffusion is fast enough to continuously reconstitute the solute cloud during dislocation motion, a homogeneous distribution of smoothly moving dislocations is observed in all alloys. Owing to the decrease of stacking-fault energy and increase of short-range order in the Cu-Al alloys a change from cell structure (Cu-5Al) to planar slip (Cu-10Al and Cu-15Al) occurs in the discontinuous glide regime; in the Cu-4.1Mn alloy with a stacking-fault energy like Cu and negligible short-range order, development of cells prevails also during discontinuous glide. The observations are discussed in terms of current views on deformation in the PLC regime.