Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

48j 2 Carbon Nanotube–Metal Nanocomposites
coatings ranging from metals to ceramics. Thermal spray coatings find widespread
applications in aerospace turbines, automotive engines, orthopedic prostheses
and electronic devices. In the process, the coating material is heated in a gaseous
medium at elevated temperatures and projected at high velocity onto a component
surface from the spray gun. Upon impact, molten splats become flattened, transfer
their heat to the cold substrate and solidify in a short period of time. Several processes
such as plasma spraying, high velocity oxyfuel spraying (HVOF), electric arc spraying
and detonation flame spraying can be used to form coatings depending on material
and desired coating performance. Synthesis of nanocomposite coatings can also be
realized via plasma spraying and HVOF [21]. In plasma spray forming (PSF), an arc is
formed between a central tungsten cathode and copper nozzle (anode) in which an
inert gas flow is passed through the arc, forming a high temperature plasma jet
( 15 000 C) from the nozzle. The coating material is fed into the plasma jet by a
carrier gas, where it is melted and propelled from the gun as a stream of molten
droplets at velocities of 400–800 ms 1 (Figure 2.1(a)). To minimize oxidation of the
Figure 2.1 Schematic diagrams of (a) plasma spraying and (b)
high velocity oxyfuel spraying. Reproduced with permission
from [21]. Copyright Ó (2006) Elsevier.