253
nanoparticles of TiN in an amorphous matrix of Si 3 N 4 exhibit hardness values as high as 50–60 GPa. The reason for this behavior
has been attributed to hindered dislocation motion and sliding
of nanoparticles. Another system, which exhibits high hardness,
consists of carbide nanoparticles (10–50 nm) embedded in amorphous carbon. This type of coating is especially useful for aerospace
applications, in which low friction, high hardness, and resistance to
corrosion are important. On the other hand, for cutting-tool applications, nanocomposite coatings are normally composed of metal
carbides embedded in a metallic matrix. Typical systems that fall
into this category are Co matrices reinforced with WC and/or TiC
and Ni matrices filled with TaC. In these nanocomposites, both the
matrix and the reinforcement particles can have nanoscale dimensions. In terms of properties, they exhibit high strength, high wear
resistance, good toughness, and thermal stability.
Multilayer nanocomposite films are also widely used for magnetic
recording media. The films are typically composed of a substrate
onto which a metallic layer followed by a magnetic layer are deposited, both with nanoscale thicknesses. To produce high magnetic
recording densities (40–100 Gbits per in
2
), the grain size of the
magnetic layer should be below 10 nm. However, at these small
grain sizes, the magnetocrystalline anisotropy has to be sufficiently
high to overcome thermal fluctuations. Examples of these nanocomposite films include multilayer structures of magnetic CoCrPt
and metallic Cr supported by a substrate.
Finally, consider the vast class of nanocomposite bio/inorganic
materials, which is a fast-growing area. Significant effort is focused
on the ability to control the nanoscale structures through novel
processing approaches. The inorganic components can be 3-D
systems such as zeolites, 2-D layered materials such as clays and
metal oxides, and even 1-D and 0-D materials such as CdS and
metal oxides. The biostructures range from proteins and DNA to
lipid cellular membranes. For example, proteins consist of domains
with very diverse properties, such as the capability for hydrogen
bonding or exhibiting acidic, basic, hydrophilic, and hydrophobic
behavior. As a result, proteins can interact with inorganic materials in a variety of ways. The same can be said about DNA, which
can be functionalized, tethered to a broad number of substances,
and self-assembled with a wide diversity of characteristics. The
general class of organic/inorganic nanocomposites may also be of
relevance to issues of bioceramics and biomineralization in which
in situ growth and polymerization of biopolymer and inorganic
matrix are occurring.
Special Cases
nanoparticles of TiN in an amorphous matrix of Si 3 N 4 exhibit hardness values as high as 50–60 GPa. The reason for this behavior
has been attributed to hindered dislocation motion and sliding
of nanoparticles. Another system, which exhibits high hardness,
consists of carbide nanoparticles (10–50 nm) embedded in amorphous carbon. This type of coating is especially useful for aerospace
applications, in which low friction, high hardness, and resistance to
corrosion are important. On the other hand, for cutting-tool applications, nanocomposite coatings are normally composed of metal
carbides embedded in a metallic matrix. Typical systems that fall
into this category are Co matrices reinforced with WC and/or TiC
and Ni matrices filled with TaC. In these nanocomposites, both the
matrix and the reinforcement particles can have nanoscale dimensions. In terms of properties, they exhibit high strength, high wear
resistance, good toughness, and thermal stability.
Multilayer nanocomposite films are also widely used for magnetic
recording media. The films are typically composed of a substrate
onto which a metallic layer followed by a magnetic layer are deposited, both with nanoscale thicknesses. To produce high magnetic
recording densities (40–100 Gbits per in
2
), the grain size of the
magnetic layer should be below 10 nm. However, at these small
grain sizes, the magnetocrystalline anisotropy has to be sufficiently
high to overcome thermal fluctuations. Examples of these nanocomposite films include multilayer structures of magnetic CoCrPt
and metallic Cr supported by a substrate.
Finally, consider the vast class of nanocomposite bio/inorganic
materials, which is a fast-growing area. Significant effort is focused
on the ability to control the nanoscale structures through novel
processing approaches. The inorganic components can be 3-D
systems such as zeolites, 2-D layered materials such as clays and
metal oxides, and even 1-D and 0-D materials such as CdS and
metal oxides. The biostructures range from proteins and DNA to
lipid cellular membranes. For example, proteins consist of domains
with very diverse properties, such as the capability for hydrogen
bonding or exhibiting acidic, basic, hydrophilic, and hydrophobic
behavior. As a result, proteins can interact with inorganic materials in a variety of ways. The same can be said about DNA, which
can be functionalized, tethered to a broad number of substances,
and self-assembled with a wide diversity of characteristics. The
general class of organic/inorganic nanocomposites may also be of
relevance to issues of bioceramics and biomineralization in which
in situ growth and polymerization of biopolymer and inorganic
matrix are occurring.
Special Cases