Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

nanoindentation, microscratching and nanowear behavior of solid surfaces and thin
films [5, 36–38]. In general, adhesive wear mechanism still operates for metallic
materials under light loads. Landman et al. used MD simulation and AFM to study
the atomistic mechanism of contact formation between a hard nickel tip and soft
gold sample [39]. Indentation of a gold surface by advancing a nickel tip resulted in
the adhesion of gold atoms to the nickel tip and formation of a connective neck of
atoms.
Interestingly, MD simulations show that CNTs can slide and roll against each other
under the application of a shear force [40, 41]. The rolling of CNTs at the atomic level
on the graphite surface has been verified experimentally by Falvo et al. using AFM [42].
They reported that rolling can occur only when both the nanotube and the underlying
graphite have long-range order. Thus, a nanotube has preferred orientations on the
graphite surface and rolling takes place when it is in atomic scale registry with the
surface. This behavior is somewhat similar to the rolling of fullerenes that act like
nanoscale ball bearings and solid lubricants [43, 44]. Despite the widespread use of
AFM for characterizing the nanowear of metallic materials, little work has been done
on nanowear of metal-CNT composites.
Up till now, there appears to be no reported work on the nanowear behavior of
metal-CNT nanocomposites in the literature. Only wear properties of metal-CNT
nanocomposites at macro-levels have been reported. Zhang and coworkers [Chap. 2,
Ref. 28] investigated the dry friction and wear behaviors of Al-Mg/MWNT nanocomposites
using a pin-on-disk test under a load of 30 N. The nanocomposites were
prepared by liquid metallurgy route in which molten Al was infiltrated into CNT-Al-
Mg preform under a nitrogen atmosphere. Figure 4.14 shows the variation of Brinell
hardness with nanotube content for the Al-Mg/MWNT nanocomposites. The hardness
of composites increases almost linearly with increasing nanotube content up to
10 vol% and then saturates with further increasing filler volume content. This leads to
Figure 4.14 Brinell hardness (HB) vs carbon nanotube volume
content for Al-Mg/MWNT nanocomposites. Reproduced with
permission from [Chap. 2, Ref. 28]. Copyright Ó (2007) Elsevier.
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