Observing formation and evolution of dislocation cells during plastic deformation

Abstract

Abstract During plastic deformation of metals and alloys, dislocations self-organise in cells, which subsequently continuously decrease in size. How and when these processes take place has remained elusive, because observations of the structural dynamics in the bulk have not been feasible. We here present X-ray diffraction microscopy sequences of the structural evolution during tensile deformation of a mm-sized aluminium (111) single crystal. The formation and subsequent development of 40,000 cells are visualised. The cells form in a stochastic, isotropic and uncorrelated manner already at 1% strain. We reveal that the cell size and dislocation density distributions are log-normal and bi-modal distributions, respectively, exhibiting scaling and maintaining a fixed volume ratio between cell interior and cell boundary. This insight leads to an interpretation of the formation and evolution steps in terms of universal stochastic multiplicative processes. This work will guide dislocation dynamics modelling, as it provides unique dynamic data and understanding.