Role of Nanosized Rotational Vortices in Cold Deformation of Metallic Glasses by the Example of Alloy Vit105

Abstract

The experimental data on the deformation of amorphous alloy Vit105 (Zr_52.5Cu_17.9Al₁₀Ni_14.6Ti₅) and its molecular dynamics simulation gave birth to new ideas about the mechanism of plastic deformation of disordered structures. A special method of torsion under hydrostatic pressure allows forming a developed deformation relief on the surface of polished specimens. Inspection of the relief points to the formation of shear bands on the surface, which can merge or branch, freely intersect or be arrested by an obstacle, forming a delta of small shear bands. Simulations based on the Morse pair potential made it possible to build a two-dimensional amorphous model and study its deformation at the atomic level. Under loading, material parts are displaced due to the appearance of atomic-scale vortices in the shear band layer by means of free volume, which is a structural feature of amorphous materials. A vortex causes redistribution of stress fields, which, when added to external stresses, are capable of activating similar vortices in the neighboring zones of the material, both in the direction of the applied stresses and along the vortex axis. In the latter case, a vortex tube is formed, which acts by the tornado mechanism. Shear is induced by the tube motion in the direction of principle shear stresses, and traces on the specimen surface are made by its screw component. An increase in the number of vortex tubes and their interaction causes a deformation band. Though playing the role of dislocations, vortex tubes are independent of specific crystalline planes and can move in arbitrary directions. This explains the experimentally observed features of deformation of amorphous alloys.