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Mapping of the Initial Volume at the Onset of Plasticity in Nanoindentation

Published online by Cambridge University Press:  01 February 2011

Tingting Zhu
Affiliation:
t.zhu@qmul.ac.uk, Queen Mary University of London, Materials, Mile End Street, London, E1 4NS, United Kingdom, 02078827418
K.M.Y. P'ng
Affiliation:
m.y.png@qmul.ac.uk, Queen Mary University of London, Centre for Materials Research, London, E1 4NS, United Kingdom
M. Hopkinson
Affiliation:
m.hopkinson@sheffield.ac.uk, University of Sheffield, Department of Electronic and Electric Engineering, Sheffield, S1 3JD, United Kingdom
A.J. Bushby
Affiliation:
a.j.bushby@qmul.ac.uk, Queen Mary University of London, Centre for Materials Research, London, E1 4NS, United Kingdom
D.J. Dunstan
Affiliation:
d.j.dunstan@qmul.ac.uk, Queen Mary University of London, Centre for Materials Research, London, E1 4NS, United Kingdom
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Abstract

Understanding the finite volume throughout which plastic deformation begins is necessary to understand the mechanics of small-scale deformation. In indentation using spherical indenters, conventional yield criteria predict that yield starts at a point on the axis and at a depth of half the contact radius. However, Jayaweera et al (Proc. Roy. Soc. 2003)[4] concluded that yield occurs over a finite volume at least 100 nm thick. Semiconductor superlattice structures, in which the stress and thickness of individual layers can be varied and in which known internal stresses can be incorporated, open up new possibilities for investigation that cannot be achieved by varying external stresses on a homogenous specimen. We have designed samples with bands of highly strained InGaAs superlattice, which are essentially bands of low yield-stress material devoid of other metallurgical artifacts. These bands are placed at different depths in a series of samples. Spherical indenters with a range of radii were used to determine the elastic-plastic transition. The stress field from different sized indenters interacts with the low yield-stress material at different depths below the surface to map out the size of the initial yield volume.

Type
Research Article
Copyright
Copyright © Materials Research Society 2008

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