On the critical conditions of the Portevin Le Chatelier effect

This paper presents a theoretical investigation of the deformation conditions under which serrated how is expected to occur. Starting from a statistical theory of the coupled dynamics of glide dislocations and solute atoms, the retardation effects associated with dynamic strain ageing are derived. This serves as an input for linear stability analysis of plastic flow. Results are available in terms of the critical plastic strains of the regime of serrated flow as a function of the applied strain rate and deformation temperature, as well as in dependence of well-defined material parameters which are easily accessible by tensile tests. The theoretical approach allows for quantitative predictions of various scenarios of serrated flow (upper and lower critical strains). In particular, an ''inverse behaviour'' (i.e. the decrease in the critical strain with increasing strain rate and/or decreasing temperature) is traced back to the same thermally activated process that causes ''normal behaviour''. (C) 1997 Acta Metallurgica Inc.