Serrated yielding: crystal viscoplastic models

Serrated yielding as a phenomenon of plastic deformation instability is found in a variety of metals and alloys in some range of strain rates and temperatures under different loading conditions. Theoretical and experimental studiesreveal the fact that the properties of polycrystalline materials on the macrolevel during inelastic deformation are significantly defined by a condition of the evolving meso- and microstructure of the material. It is necessary to create models which describe plastic instability and microstructural self-organization process that can ultimately lead to aspontaneous appearance of strain localization. The first part of the review (Trusov P.V., ChechulinaЕ.А. Serrated yielding: Physical mechanisms, experimental dates, macrophenomenological models. PNRPU Mechanics Bulletin. 2014. No. 3. - Pp. 186-232. doi:10.15593/perm.mech/2014.3.10) considersthe works describing physical mechanisms, experimental studies of serrated yielding and the best known macrophenomenological models. However, a correct description of plastic deformation, its heterogeneity and account for all its attendant real physical mechanisms need to study the material behavior not on the macrolevel, but on a lower meso- and microstructural levels. Plastic deformationis associated with a non-uniform motion of elementary carriers of plastic flow, i.e. dislocations (in time and space). Dislocations and dislocation barriers (Lomer-Cottrell, immobile dislocations) and nondislocation barriers (clouds of impurity atoms, solid particles, solids inclusionof the secondary phase etc.) make it possible to describe the multilevel model at meso- and microlevels. In this part of the review some of the theoretical works based on the crystal plasticity are analyzed,thus describing deformation features of alloys in a wide range of temperatures and strain rates in which diffusion processes have a significant influence on the materials behavior. Special attention is paid to describingthe Portevin-Le Chatelier (PLC) effect; the majority of the authors think that it appears due to the interaction of dislocations with impurity atoms.