Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

Figure 2.19 (a) Low and (b) high magnification SEM images of
mechanically milled Cu/MWNT powder. Reproduced with
permission from [81]. Copyright Ó (2006) Elsevier.
so on. It is necessary to optimize milling conditions to obtain uniform dispersion of
CNTs throughout entire copper matrix.
Spark plasma sintering (SPS) is an effective tool to sinter and consolidate powders
under the application of an external pressure at relatively low temperatures and short
periods of time (Figure 2.21). It is particularly useful for sintering nanopowders
because the grain coarsening problem can be minimized or avoided. Retention of
nanograins enables the resulting composites exhibiting enhanced mechanical
strength and hardness. SPS is a pressure assisted sintering technique in which a
pulsed current is applied to the upper and lower graphite plungers such that high
temperature plasma is generated between the gaps of electrodes. In this case,
uniform heating can be achieved for sintering compacted powder specimen. Sintering
can be performed at wide range of pressures and temperatures. The technique is
widely used to prepare densely structural ceramics, nanoceramics and their composites
as well as bulk CNTs [82–84].
Figure 2.20 Optical micrographs of spark plasma sintered (a) Cu/
5 vol% MWNT and (b) Cu/10 vol% MWNT nanocomposites.
Reproduced with permission from [81]. Copyright Ó (2006)
Elsevier.
2.7 Copper-Based Nanocompositesj67