Observation and modelling of propagating Portevin-Le Chatelier deformationbands in Cu-15 at.% Al polycrystals

The nucleation and propagation of Portevin-Le ChaAtelier (PLC) deformation bands have been studied by means of a novel multizone laser scanning extens ometer providing information on the local development of strain along the m ain part of the specimen, in addition to the conventional measurement of st ress serrations. This permits us to distinguish clearly between the bands o f types A, B a nd C, and to explore their ranges of existence at various te mperatures, stresses and strain rates as well as transitions between them a long the stress-strain curve. The laser extensometer provides independent d ata on the propagation velocity, concentrated strain and width of the bands . These experimental data are compared with a recent theoretical space-time analysis of propagating PLC bands, which combines explicitly a physical de scription of the kinetics of dynamic strain ageing and plastic deformation including the effect of long-range dislocation interactions. The model corr ectly predicts the above band parameters and their dependences on the defor mation rate and specimen thickness.