Biomedical Engineering Reference
In-Depth Information
category MMC encompasses a wide range of scales and microstructures
(Davis and Ward, 1993).
Currently, MMCs can be classified into three categories:
.
particle reinforced MMCs
.
short fibre or whisker reinforced MMCs
.
continuous fibre or sheet reinforced MMCs.
Particle reinforced MMCs are of the most interest since they are isotropic,
easier to manufacture, and often lower cost. The properties of particle
reinforced MMCs are greatly affected by particle size and distribution.
Research on particle reinforced MMCs has shown that tensile strength and
ductility decrease with increasing reinforcement size. Nanosized particles are
predicted to enhance the properties of MMCs more than their microsized
counterparts, creating metal matrix nanocomposites (MMNCs) (Ajayan
et al., 2003). Nanoparticle and carbon nanotube (CNT) reinforced MMNCs
are the most commonly researched types.
MMNC research did not attract as much interest as ceramic and polymer
matrix nanocomposites until recently, mostly due to the inferior mechanical
properties reported so far. Despite some improvements in hardness and
wear resistance (Kim et al., 2007; Laha et al., 2009), the overall properties
did not achieve predicted values due to the existence of defects, such as
porosity and agglomeration of nanoparticles. However, the potential
development of a novel nanocomposite with excellent mechanical and
unique physical properties has generated an increasing amount of research
interest in recent years.
MMNCs have shown numerous different characteristics compared to
composites with microsize reinforcement. When the dimension of a material
approaches the nanoscale, new properties emerge due to size confinement,
quantum phenomena and Coulomb blockage. Varadan et al. (2010)
summarized the special properties of nanomaterials, including their
structural, thermal, chemical, mechanical, magnetic, optical, electronic
and biological properties. When it comes to MMNCs, a couple of
characteristics should be noted.
.
When the reinforcement scales down to nanosize, due to the
agglomeration of nanoparticles, the fabrication of MMNCs is much
more difficult than the production of MMCs.
.
The reinforcement mechanism is different in MMNCs and MMCs.
Adding microsize reinforcement has successfully improved some
mechanical properties of a metal matrix. The strengthening mechanism
is more due to the hard reinforcement to stop the movement of
dislocation. Due to the small reinforcement size, MMNCs are reinforced
