Plasticity experiments with single dislocation resolution in indentation and wear
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-01-01 |
| Journal | eScholarship@McGill (McGill) |
| Authors | Philip Egberts |
Abstract
Section titled “Abstract”Plasticity experiments have been conducted with single dislocation resolution in both indentation and wear studies using atomic force microscopy (AFM). The high force sensitivity and the small tip radii in AFM permit the measurement of the nucleation of single dislocations in plastically deformed nanoscale volumes. Nanoscale mechanical testing in an ultra-high vacuum (UHV) environment allows for the preparation of oxide-free surfaces, required for direct comparison between atomistic simulation and experiment. Moreover, nanoscale mechanical testing often shows increased strength compared to what is observed in macroscale testing, motivating the use of atomistic simulation to gain insight into new deformation mechanisms. Indentation experiments show that it is possible not only to observe single dislocation events but also determine the glide vector of the dislocation in three dimensions on KBr(001). Discontinuous displacements of the tip during indentation in both normal and lateral directions are indicative of yielding events, referred to as pop-ins. The measured displacement of the tip into the material during these events is on the order of one Ångström or less when blunt diamond coated tips are used as indenters. Larger pop-in displacements are measured with sharper probes, resulting from the localization of stress near the surface. Only with the use of AFM can such small, Ångström-sized pop-in displacements be observed. Indentation creep studies indicate that creep in nanoscale volumes is accommodated only through dislocation nucleation and glide. A comparison between creep measured with AFM-based indentation and instrumented nanoindentation highlights the importance of dislocation nucleation and glide at this length-scale. High resolution imaging of the indented structure on KBr(001) allows for the identification of dislocations and charges associated with them. Wear experiments have demonstrated the contribution of dislocations to wear on the atomic scale. The role of dislocations in wear experiments has been observed through the similar dislocation structures typically surrounding scratches and indents, as well as in pop-ins observed while scratching. The measured friction coefficient in nanoscale wear experiments is closer to those typically reported in macroscopic experiments. This finding suggests that while single-asperity experiments at low loads on flat surfaces may produce no or little wear, friction of real rough surfaces always involves some wear and plastic deformation of microscopic contacts between the two surfaces.