Biomedical Engineering Reference
In-Depth Information
reinforcement used in the system. For ex-situ manufacturing processes, a
successful material system depends on good wettability between the ceramic
and metal area and the surface bonding between the two materials. Different
metal matrix and reinforcement systems used in research are summarized in
this chapter.
Experiments have been conducted to fabricate, observe reinforcement/
matrix interfaces, and improve the mechanical and physical properties of
MMNCs. Despite the many publications in this field, limited achievement
has been made to date to improve matrix properties without the attenuation
of some other properties. This chapter, summarizes these achievements and
limitations.
The majority of current research on MMNCs focuses on process
development. The MMNC fabrication process can be categorized into in-
situ and ex-situ.Inin-situ MMCs, the reinforcements are formed by
chemical reactions between elements or between elements and compounds
during the manufacturing process. The advantages of in-situ methods are:
the formation of reinforcements that are thermodynamically stable; the
reinforcing particles surfaces are clean, resulting in strong interfacial
bonding; finer particle size; a more uniform distribution in the matrix
(Shehata et al., 2009). For ex-situ manufacturing, the advantage is
potentially being able to produce bulk material. Due to the poor wettability
between a metal and ceramic reinforcement, and also because nanoparticles
tend to agglomerate due to their electrostatic and van der Waals forces in
the liquid mixing process, a limited amount of MMNCs have reached their
predicted mechanical properties.
Based on all the recent research on MMCs, critical issues that need to be
solved to successfully fabricate MMNCs are as follows.
.
Dispersion. The distribution of reinforcing particulates has to be
uniform to achieve predicted mechanical properties. However, this is
extremely difficult because nanoparticles tend to agglomerate. Particle
cluster will be extremely harmful for MMNCs.
.
Reactivity. The research shows that some nanoparticle reactivity
decreases as size increases (Ramakrishna and Ghosh, 2003). The effect
of particle size on the reactivity of nanoparticles may lead to interesting
chemical reactions between the interface of the metal matrix and
ceramic reinforcement for in-situ and ex-situ MMNC manufacturing
processes.
.
Thermal stability. When particles scale down to nanosize, the thermal
stability of ceramic particles can be affected (Park and Lee, 2009).
.
Wettability. Wettability between ceramic particles and metal is poor.
Copper coating and acid treatment have been used to improve the
wettability between CNTs and metals (Neubauer et al., 2010). A cost-
