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A new view of the onset of plasticity during the nanoindentation of aluminium

A new view of the onset of plasticity during the nanoindentation of aluminium In nanoscale contact experiments, it is generally believed that the shear stress at the onset of plasticity can approach the theoretical shear strength of an ideal, defect-free lattice 1,2,3,4 , a trend also observed in idealized molecular dynamics simulations 5,6,7,8,9 . Here we report direct evidence that plasticity in a dislocation-free volume of polycrystalline aluminium can begin at very small forces, remarkably, even before the first sustained rise in repulsive force. However, the shear stresses associated with these very small forces do approach the theoretical shear strength of aluminium (∼2.2 GPa). Our observations entail correlating quantitative load–displacement measurements with individual video frames acquired during in situ nanoindentation experiments in a transmission electron microscope. We also report direct evidence that a submicrometre grain of aluminium plastically deformed by nanoindentation to a dislocation density of ∼1014 m−2 is also capable of supporting shear stresses close to the theoretical shear strength. This result is contrary to earlier assumptions that a dislocation-free volume is necessary to achieve shear stresses near the theoretical shear strength of the material 5,6,7,8,9 . Moreover, our results in entirety are at odds with the prevalent notion that the first obvious displacement excursion in a nanoindentation test is indicative of the onset of plastic deformation. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Nature Materials Springer Journals

A new view of the onset of plasticity during the nanoindentation of aluminium

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References (30)

Publisher
Springer Journals
Copyright
Copyright © 2006 by Nature Publishing Group
Subject
Materials Science; Materials Science, general; Optical and Electronic Materials; Biomaterials; Nanotechnology; Condensed Matter Physics
ISSN
1476-1122
eISSN
1476-4660
DOI
10.1038/nmat1714
Publisher site
See Article on Publisher Site

Abstract

In nanoscale contact experiments, it is generally believed that the shear stress at the onset of plasticity can approach the theoretical shear strength of an ideal, defect-free lattice 1,2,3,4 , a trend also observed in idealized molecular dynamics simulations 5,6,7,8,9 . Here we report direct evidence that plasticity in a dislocation-free volume of polycrystalline aluminium can begin at very small forces, remarkably, even before the first sustained rise in repulsive force. However, the shear stresses associated with these very small forces do approach the theoretical shear strength of aluminium (∼2.2 GPa). Our observations entail correlating quantitative load–displacement measurements with individual video frames acquired during in situ nanoindentation experiments in a transmission electron microscope. We also report direct evidence that a submicrometre grain of aluminium plastically deformed by nanoindentation to a dislocation density of ∼1014 m−2 is also capable of supporting shear stresses close to the theoretical shear strength. This result is contrary to earlier assumptions that a dislocation-free volume is necessary to achieve shear stresses near the theoretical shear strength of the material 5,6,7,8,9 . Moreover, our results in entirety are at odds with the prevalent notion that the first obvious displacement excursion in a nanoindentation test is indicative of the onset of plastic deformation.

Journal

Nature MaterialsSpringer Journals

Published: Aug 13, 2006

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