Civil Engineering Reference
In-Depth Information
Chan (2006) discloses novel methods of depositing a nanocomposite
coating of SS and a metallic carbide or metallic nitride onto a solid metal-
lic substrate (e.g., SS) to increase its surface hardness. Unlike the continu-
ous deposition process, very thin layers (e.g., 5-10 nm per layer) of such
nanocomposite coating are deposited by reactive sputtering in a C or N
2
gas plasma, using pure SS and Cr targets or their alloy targets. When the
substrate is away from the deposition locations, the deposited SS and CrC
(or CrN) phases were reported to relax into 'their most thermodynami-
cally suitable sites'. The hardness improvement was achieved by forming
the nanocomposite structure in which the CrC nanophases precipitated
along the SS GBs. This method features a clean process for obtaining
a hard, wear-resistant, and corrosion-resistant coating with an SS-like
appearance.
Namavar (2006) discloses an invention that provides metallic compo-
nents (e.g., SS) with integrally formed, homo-metallic protective coatings
on their surfaces. The deposited substance and the bulk substrate have at
least one metallic constituent element in common; and the formed coatings
feature crystalline grains preferably in a range of about 10-200 nm and thus
an enhanced hardness and a high degree of resistance to corrosion and
wear. To improve the adhesion of the coating to the substrate, the average
crystalline grain size can decrease continuously from the substrate to the
coating within the transition zone.
Detor and Schuh (2006) disclose the use of bipolar pulsed current (BPP)
to produce alloy deposits with a specifi ed nanocrystalline average grain size
and thus superior macroscopic quality and/or resistance to corrosion and
abrasion. Polarity ratio (characterized by the amplitude and/or duration of
the negative pulse relative to those of the positive pulse) was used to enable
'grading and layering of nanocrystalline crystal size and/or composition
within a deposit' without introducing voids and cracks. Relative to tradi-
tional microcrystalline metals, the nanocrystalline metal coatings with
nano-grains are expected to show exceptional combination of properties
such as excellent corrosion and wear resistance, enhanced yield strength
and ductility, and desirable magnetic properties.
Finally, nanotechnology has been employed to alter the steel/electrolyte
interface, by forming nano-modifi ed polymeric coating on steel. The incor-
poration of nano-sized particles (e.g., SiO
2
, Fe
2
O
3
, and halloysite clay) into
conventional polymer coatings can signifi cantly enhance the anti-corrosive
performance of such coatings on steel substrates (Shi
et al.
, 2009). A com-
prehensive review on this subject, however, is beyond the scope of this
chapter. A recent review in 2007 by Saji and Thomas discussed the incor-
poration of nanoparticles in ceramic coatings, polymer coatings, and hybrid
sol-gel systems for improved properties (e.g., resistance to corrosion and
high-temperature oxidation, self-cleaning, and anti-fouling).
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