STZ vortex unit – the key to understand and control shear banding in metallic glasses

  • Date: Jul 6, 2021
  • Time: 02:00 PM - 03:00 PM (Local Time Germany)
  • Speaker: Dr. Daniel Şopu
  • Group Leader at the Erich Schmid Institute of Materials Science in Austria
  • Location: Online
  • Room: Virtual Lecture
  • Host: Dr. Tobias Brink
STZ vortex unit – the key to understand and control shear banding in metallic glasses

Shear bands (SBs) are plasticity carriers of metallic glasses (MGs) and the rapid runaway of a detrimental SB often results in catastrophic failure of MGs under imposed stresses. The ability to control plastic deformation of MGs is based on the capacity to influence the percolation of shear transformation zones (STZs) that ultimately leads to SB formation. STZs remain the fundamental unit to explain plastic flow in MGs. Although STZs have been known and characterized for decades now, the morphological and dynamical characteristics of STZs are not fully understood, yet. In this presentation, by means of molecular dynamics and athermal quasi-static simulations, I propose a novel atomic-level mechanism underlying the STZ activation and percolation processes that could provide a sound and realistic microscopic description of shear band formation and propagation mechanisms in MGs. The mechanism is based on the autocatalytic generation of successive strong strain (STZ) and rotation fields (vortex-like motion), leading to STZ percolation and, ultimately, to the formation of a shear band. These results could build a bridge between the discrete nature of STZs at the atomic-level and the rather continuous character of shear bands at the microscale. So far, the STZ-vortex mechanism allowed to follow the structural and dynamical evolution during shearing in MGs and provided an atomistic description of deformation mechanisms like shear band formation and interaction, shear band branching and multiplication, or shear band blocking and deflection. Additionally, the STZ-vortex mechanism was of primary importance for understanding the brittle-to-ductile transition from cracking to localized shear banding and homogeneous deformation. Through the proper control of the STZ-vortex sequence, one could handle the shear band dynamics and avoid runaway instability, thereby improving the plastic deformability of metallic glasses at room temperature

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