When two or more constituent materials are combined on a microscopic scale it results
in a composite material whose physical properties are very different than the properties of the
constituents due to their synergy. In composites when the reinforcing phase is synthesized
within the matrix during fabrication it is called in-situ composite. This contrasts with ex-situ
composites where the reinforcing phase is synthesized separately and then integrated during
composite fabrication by solidification processing or powder metallurgy route. Because of the
formation of ultra fine and stable ceramic reinforcements, the in-situ MMCs are found to
exhibit excellent properties.
When different kinds of reinforcements (particulates, fibres etc.) is added into a single
matrix, resulting a hybrid composites. In hybrid composites, matrix may be of metal,
polymer, ceramic and carbon. The hybrid composite which has two or more kinds of
reinforcement, the benefit of one type of reinforcement could complement with what are
lacking in the other. These hybrid composites show a better performance with an optimum
cost (Jacob et al., 2004).
A nano composite is a multiphase solid material where one of the phases has one, two or
three dimensions of less than 100 nano meters (nm), or structures having nano scale repeat
distances between the different phases that make up the materials. In the broadest sense this
definition can include porous media colloids, gel and copolymers, but is more usually taken
to mean the solid combination of a bulk matrix and nano dimensional phases differing in
properties due to dimensional in structure and chemistry.
Aluminium matrix composites (AMCs) refer to the class of light weight high performance
aluminium centric material systems. The reinforcement in AMCs could be in the form of
continuous/discontinuous fibres, whisker or particulates, in volume fractions ranging from a
few percent to 70%. Properties of AMCs can be tailored to the demands of different industrial
applications by suitable combinations of matrix, reinforcement and processing route.
Presently several grades of AMCs are manufactured by different routes. In the last few years,
AMCs have been utilised in high-tech structural and functional applications including
aerospace, defence, automotive, and thermal management areas, as well as in sports and
However, in the 1990s a new field of artificial self-healing materials has emerged. These
materials, inspired by the ability for selfhealing in biological objects, are designed in such a
way that they include mechanisms that can at least partially repair damage, such as voids and
cracks, and partially or completely restore macroscopic material properties. Usually, a
healing agent (often a liquid) is stored in the matrix of the material and when a cavity (a crack
or void) is formed, it fills the cavity and closes it due to a chemical reaction or a phase
transition (e.g., solidification). The healing can be autonomous (without human intervention)
and non autonomous. The latter require some external intervention, such as heating the
material to trigger the repair process (Ghosh 2009; Zwaag 2007).
We live in an interesting time for materials scientists and engineers, when new advanced
technology gives us the ability to control structure and properties at the micro- and nanoscale,
and when new experimental discoveries in biology give us the insight of how materials and
tissues in living nature achieve their remarkable properties. At this interface, the new fields of
advanced, nanostructured, smart, functional, and biomimetic materials have emerged.