Nonlinear Dynamics of Individual Portevin-Le Chatelier Deformation Bands

Based on high-speed dynamics studies with a temporal resolution of up to 20 mu s and a spatial resolution of up to 10 mu m/px, a classification is proposed for the nucleating Portevin-Le Chatelier deformation bands (embryo bands), which includes four types of bands depending on the nature of the interaction with other bands and the sample surface (a polycrystalline aluminum-magnesium alloy as an example). It was found that all types of embryo bands demonstrate nonlinear dynamics with a sharp acceleration of the embryo band tip and the growth rate of the volume at the final stage before reaching the surface of the sample. A phenomenological model for the nonlinear growth of embryo bands is proposed, which qualitatively explains the exponential self-acceleration stage observed experimentally. The sharp absorption of acoustic noise at the stage of accelerated band growth is discussed.