Abstract
It has been reported previously that, for single and polycrystalline
copper (fcc), the indentation size effect and the grain size effect (GSE)
can be combined in a single length-scale-dependent deformation
mechanism linked to a characteristic length-scale calculable by
a dislocation-slip-distance approach (X. D. Hou and N. M. Jennett,
‘Application of a modified slip-distance theory to the indentation of
single-crystal and polycrystalline copper to model the interactions
between indentation size and structure size effects,’ Acta Mater., Vol.
60, pp. 4128–4135, 2012). Recently, we identified a ‘lateral size effect
(LSE)’ in scratch hardness measurements in single crystal copper,
where the scratch hardness increases when the scratch size is reduced
(A. Kareer, X. D. Hou, N. M. Jennett and S. V. Hainsworth ‘The existence
of a lateral size effect and the relationship between indentation and
scratch hardness’ Philos. Mag. published online 24 March 2016). This
paper investigates the effect of grain size on the scratch hardness
of polycrystalline copper with average grain sizes between 1.2
and 44.4 μm, when using a Berkovich indenter. Exactly the same
samples are used as in the indentation investigation by Hou et al.
(‘Application of a modified slip-distance theory to the indentation of
single-crystal and polycrystalline copper to model the interactions
between indentation size and structure size effects,’ Acta Mater., Vol.
60, pp. 4128–4135, 2012). It is shown that, not only does the scratch
hardness increase with decreasing grain size, but that the GSE and
LSE combine in reciprocal length (as found previously for indentation)
rather than as a superposition of individual stresses. Applying the
same (as indentation) dislocation-slip-distance-based size effect
model to scratch hardness yielded a good fit to the experimental
data, strongly indicating that it is the slip-distance-like combined
length-scale that determines scratch hardness. A comparison of the fit
parameters obtained by indentation and scratch on the same samples
is made and some distinct differences are identified. The most striking
difference is that scratch hardness is over four times more sensitive to
grain size than is indentation hardness.
Original language | English |
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Pages (from-to) | 3414-3429 |
Number of pages | 16 |
Journal | Philosophical Magazine |
Volume | 96 |
DOIs | |
Publication status | Published - 5 Oct 2016 |
Keywords
- Lateral size effect
- indentation size effect
- polycrystalline copper
- scratch testing
- scratch hardness
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Profiles
-
Nigel Jennett
- Institute for Future Transport and Cities - Professor of Materials, Mechanics and Measurement
Person: Teaching and Research