Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

Figure 2.6 (a) Low and (b) high magnification SEM fractographs
of Al./0.5wt% MWNT strip. Several individual nanotubes can be
seen in (b). Reproduced with permission from [30]. Copyright Ó
(2008) Elsevier.
For metal-matrix microcomposites, the relative ratio of the matrix particle size to
reinforcement particle size (RPS) is used as an indicator for homogeneous dispersion
of microparticles in the metal matrix. In other words, the degree of homogeneity
is expressed in terms the RPS ratio. Higher RPS ratio favors particle clustering
whereas low RPS ratio facilitates homogeneous distribution of ceramic microparticles
in the metal matrix [31–33]. It is considered that a relatively large RPS ratio
between metal powders and CNT particles promotes the formation of nanotube
clusters in the CNT-reinforced metals. Accordingly, fabrication methods based
on PM have overwhelmingly concentrated on improving nanotube dispersion in
order to achieve desired mechanical characteristics in the resulting nanocomposites
[34–41].
More recently, dispersion of CNTs homogeneously in metals has been achieved by
employing mechanical alloying (MA). This technique is used widely to obtain
Figure 2.7 SEM fractograph of Al/1 wt% MWNT strip showing
nanotube clusters. Reproduced with permission from [30].
Copyright Ó (2008) Elsevier.
2.4 Aluminum-Based Nanocompositesj53