Abstract

AbstractThe chapter is devoted to the analysis of the features of local structural rearrangementsin nanostructured materialsunder shear loadingand nanoindentation. The study was carried out using molecular dynamics-based computer simulation. In particular, we investigated the features of symmetric tilt grain boundary migration in bcc and fcc metals under shear loading. The main emphasis was on identifying atomic mechanisms responsible for the migration of symmetric tilt grain boundaries. We revealed that grain boundaries of this type can move with abnormally high velocities up to several hundred meters per second. The grain boundary velocity depends on the shear rate and grain boundary structure. It is important to note that the migration of grain boundary does not lead to the formation of structural defects. We showed that grain boundary moves in a pronounced jump-like manner as a result of a certain sequence of self-consistent displacements of grain boundary atomic planes and adjacent planes. The number of atomic planes involved in the migration process depends on the structure of the grain boundary. In the case of bcc vanadium, five planes participate in the migration of the Σ5(210)[001] grain boundary, and three planes determine the Σ5(310)[001] grain boundary motion. The Σ5(310)[001] grain boundary in fcc nickel moves as a result of rearrangements of six atomic planes. The stacking order of atomic planes participating in the grain boundary migration can change. A jump-like manner of grain boundary motion may be divided into two stages. The first stage is a long time interval of stress increase during shear loading. The grain boundary is motionless during this period and accumulates elastic strain energy. This is followed by the stage of jump-like grain boundary motion, which results in rapid stress drop. The related study was focused on understanding the atomic rearrangements responsible for the nucleation of plasticity near different crystallographic surfaces of fcc and bcc metals under nanoindentation. We showed that a wedge-shaped region, which consists of atoms with a changed symmetry of the nearest environment, is formed under the indentation of the (001) surface of the copper crystallite. Stacking faults arise in the (111) atomic planes of the contact zone under the indentation of the (011) surface. Their escape on the side free surface leads to a step formation. Indentation of the (111) surface is accompanied by nucleation of partial dislocations in the contact zone subsequent formation of nanotwins. The results of the nanoindentation of bcc iron bicrystal show that the grain boundary prevents the propagation of structural defects nucleated in the contact zone into the neighboring grain.

Highlights

  • The behavior of the material in contact zones is a complex multiscale process [1], which depends on a number of parameters: the roughness of the contacting surfaces, the chemical composition of materials, loading parameters, etc. [2]

  • Still many issues related to the nucleation and development of plastic deformation, structural transformations, and wear in the contact zones in nanostructured metallic materials remain debatable

  • In [17] it was shown that some types of grain boundaries (GB) in fcc materials can migrate with abnormally high speeds under shear loading

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Summary

Introduction

The behavior of the material in contact zones is a complex multiscale process [1], which depends on a number of parameters: the roughness of the contacting surfaces, the chemical composition of materials, loading parameters, etc. [2]. Still many issues related to the nucleation and development of plastic deformation, structural transformations, and wear in the contact zones in nanostructured metallic materials remain debatable This is due to both the great variety of chemical composition and internal structure of nanostructured materials, and the difficulties in their experimental studying at the microscopic level, associated with small spatial and temporal intervals of the processes. In [17] it was shown that some types of GBs in fcc materials can migrate with abnormally high speeds under shear loading This can lead to a change in the structure and tribological parameters of the material in the friction zone. Features of the behavior of materials during contact interaction are presented by studying atomic mechanisms of nucleation and development of plasticity in fcc copper and bcc vanadium metals with an ideal structure and GBs under nanoindentation

Materials and Methods
Features of Symmetric Tilt Grain Boundary Migration in Metals
Peculiarities of Plasticity Nucleation in Metals Under Nanoindentation
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