Letter abstract
Nature Materials 5, 697 - 702 (2006)
Published online: 13 August 2006 | doi:10.1038/nmat1714
Subject Categories: Metals and alloys | Mechanical properties | Characterisation and analytical techniques
A new view of the onset of plasticity during the nanoindentation of aluminium
Andrew M. Minor1, S. A. Syed Asif2, Zhiwei Shan1, Eric A. Stach3, Edward Cyrankowski2, Thomas J. Wyrobek2 & Oden L. Warren2
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 lattice1, 2, 3, 4, a trend also observed in idealized molecular dynamics simulations5, 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 material5, 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.
- National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Hysitron Incorporated, 10025 Valley View Road, Minneapolis, Minnesota 55344, USA
- School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA
Correspondence to: Oden L. Warren2 e-mail: owarren@hysitron.com
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