Mikhail Lebyodkin
CNRS, France
Title: Correlated versus random behavior of dislocations in jerky flow of Al-Mg alloys
Biography
Biography: Mikhail Lebyodkin
Abstract
The interest to jerky flow in dilute alloys or the Portevin-Le Chatelier (PLC) effect has not diminished since it was discovered a century ago. One reason for such sustaining interest is that the PLC effect is undesirable in practice since it impedes the formability of alloys. On the other hand, it is a striking example of dislocations self-organization that gives rise to a complex strain heterogeneity evolution and serrated deformation curves. The microscopic mechanism of plastic instability is understood rather well and is generally attributed to dynamical pinning of dislocations by solute atoms. Indeed, since this additional pinning is controlled by a balance between the solute diffusion rate and the plastic strain rate, it leads to a negative resistance of the material to loading: the stronger the strain rate, the lower the deforming stress. The feature of negative resistance is a well-known mobile of unstable behavior of dynamical systems. However, the knowledge of the microscopic mechanism is insufficient to model real behavior which requires understanding the instability development involving complex collective dynamics of dislocations. The observed behaviors depend on the strain rate, temperature, microstructure and even the scale of observation, but display some reproducible features that testify the existence of specific dynamical mechanisms. Uncovering these mechanisms has become one of important fields of research since two decades. In the present paper, the PLC effect is investigated using statistical analysis of plastic activity in Al-Mg alloys on distinct scales of observation, namely, the macroscopic scale of stress serrations and a mesoscopic scale pertaining to the accompanying acoustic emission, as well construction of spatiotemporal patterns characterizing the local strain field evolution. In particular, it is found that the extreme grain refinement by recently developed methods of severe plastic deformation strongly affects the dynamical mechanisms controlling the unstable plastic flow.
Recent Publications
1. Lebyodkin MA, Shashkov IV, Lebedkina TA, Mathis K, Dobron P, Chmelik F (2013) Role of superposition of dislocation avalanches on the statistics of acoustic emission during plastic deformation. Phys. Rev. E 88: 042402.
2. Lebedkina TA, Lebyodkin MA, Lamark TT, Janecek M, Estrin Y (2014) Effect of equal channel angular pressing on the PortevinLe Chatelier effect in an Al3Mg alloy. Mater. Sci. Eng. A 615: 7-13.
3. Zhemchuzhnikova D, Lebyodkin M, Lebedkina T, Kaibyshev R (2015) Unusual behavior of the Portevin-Le Chatelier effect in an AlMg alloy containing precipitates. Mater. Sci. Eng. A 639: 37-41.
4. Abobaker M, Bouaziz O, Lebyodkin M, Lebedkina T, Shashkov IV (2015) Avalanche dynamics in crumpled aluminum thin foils. Scripta Mater. 99: 17-20.
5. Amouzou K, Richeton T, Roth A, Lebyodkin M, Lebedkina T (2016) Micromechanical modeling of hardening mechanisms in commercially pure alpha-titanium in tensile condition. Intern. J. Plasticity 80: 222-240.