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, a trend also observed in idealized molecular dynamics simulations. Here we report direct evidence that plasticity...

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Bibliographic Details
Published in:Nature materials Vol. 5; no. 9; pp. 697 - 702
Main Authors: Warren, Oden L, Minor, Andrew M, Syed Asif, S. A, Shan, Zhiwei, Stach, Eric A, Cyrankowski, Edward, Wyrobek, Thomas J
Format: Journal Article
Language:English
Published: England Nature Publishing Group 01-09-2006
Subjects:
Aluminum
Materials science
Microscopy
Nanotechnology
Plasticity
Shear stress
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Summary: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, a trend also observed in idealized molecular dynamics simulations. 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. 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.
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ISSN:1476-1122
1476-4660
DOI:10.1038/nmat1714