Correlation of temporal instabilities and spatial localization during Portevin–LeChatelier deformation of Cu–10 at.% Al and Cu–15 at.% Al

Abstract

The Portevin–LeChatelier (PLC) effect with characteristic temporal instabilities in the recorded stress is closely associated with local inhomogeneities of deformation. Measurements on Cu–10 at.% Al and 15 at.% Al polycrystals by means of a novel laser scanning extensometer, which provides quasi-simultaneous spatial resolution along the main part of the specimen, have been used for an unambiguous characterization of the PLC deformation bands of type A (continuous propagation of single band along the specimen), type B (discontinuous band propagation) and type C (stochastic nucleation of single bands along the specimen), supplementing and correcting the common characterization from the load serrations. Surprising transitions between the types have been detected in the effective stress versus temperature (or versus strain rate) diagram. The parameters of type A bands (local band strain, band width, propagation rate) have been measured at various temperatures in dependence of grain size, specimen thickness and imposed deformation rate, and are compared with predictions of a recent theoretical treatment.