DESIGN, ASSEMBLY AND CHARACTERIZATION OF COMPOSITE ...

Various FGM coating processes are available, including plasma spraying, electroforming
and vapor deposition.
Plasma Spray Forming uses a plasma gun to rapidly heat and accelerate particles
below 100 µm in diameter. 81 The particles are melted and flattened upon impact with a
solid substrate, as illustrated in Figure 2.36. This feature, especially carried in low-
pressure or vacuum environments, enables the deposition of relatively dense coatings,
and reduces the need for post-treatment. The major requirement to this process is that the
powder material not be decomposed. For fabrication of ceramic-metal FGMs, plasma
spraying is an attractive method because it can simultaneously melt ceramic and metal
phases, blending them in ratios controlled through relative powder feeding rates.
Figure 2.36 Schematic of plasma spraying of FGM coating. 45
Thermal Spray Deposition sprays a jet of atomized molten metal onto a substrate
and builds up a metal layer upon solidification. This process may fabricate composites,
by injecting reinforcing particles into the metal spray. 82 The reinforcing particles,
typically ceramics, generally remain solid and are coated by metal droplets to form a
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