Atomic-Level Observation of Disclination Dipoles in Mechanically Milled, Nanocrystalline Fe

Abstract

Plastic deformation of materials occurs by the motion of defects known as dislocations and disclinations. High-resolution transmission electron microscopy was used to directly reveal the individual dislocations that constitute partial disclination dipoles in nanocrystalline, body-centered cubic iron that had undergone severe plastic deformation by mechanical milling. The mechanisms by which the formation and migration of such partial disclination dipoles during deformation allow crystalline solids to fragment and rotate at the nanometer level are described. Such rearrangements are important basic phenomena that occur during material deformation, and hence, they may be critical in the formation of nanocrystalline metals by mechanical milling and other deformation processes.

Dislocation nucleation and motion observed in a plasma crystal

“…This motivates investigations on a "sub-dislocation" scale. In regular solids dislocation dynamics is almost impossible to study experimentally at an atomistic level [15] because of the small distances between the atoms (or molecules), high characteristic frequencies, and the lack of experimental techniques of visualizing the motion of individual atoms or molecules in regular matter at relevant space and time scales. Therefore, an experimental model system where the motion of individual "atoms" can be observed in real time, is highly desirable.…”

Disordered Nanocrystalline SuperconductingPbMo6S8with a Very Large Upper Critical Field

“…High energy mechanical milling has been used as an effective way to synthesize large quantities of disordered, nanocrystalline and amorphous powders containing large amounts of vacancies, dislocations, and grain boundaries [11,12]. Nanocrystalline bulk materials can then be obtained with different levels of disorder by subsequently compacting and heat treating the milled powder [13,14].…”

Visco-Plastic Flow of Metal in Dynamic Conditions of Complex Strain Scheme

“…[21] Slip along grain boundaries, Coble creep, and the mechanism involving grain rotation [22][23][24] recently became the subject of particular interest during the simulation and analytical studies. [25][26][27][28][29] A concept that combines the phenomenon of superplasticity and slip along the grain boundaries, despite many controversial assumptions, has been found to be justified. [25,30,31] On the other hand, the smaller the grains, the larger the area occupied by the boundaries; their spatial distribution is also better, allowing a long-range intercrystalline shear.…”