*2.2.4 Spray deposition*

The spray deposition is a technique in which droplets of molten metal or continuous feeding of cold metal is spread over rapid heat injection zone. The process is adopted for bulk production by directing the atomized stream of droplets on the substrate. The adaptation of this technique for the building of MMCs by injecting ceramic powder into spray has commercially succeeded. The droplet/powder velocities are typically 20-40 m/s, and the thin layer of semisolid reinforcement is present on the surface of the ingot. The MMCs produced by spray deposition often exhibit inhomogeneous distribution, and the ceramic layer is normal to growth direction, which leads to hydrodynamic instabilities in powder injection. The porosity in MMCs in the as-sprayed state is typically 5–10%.

In the chemical vapor deposition process, the vapors react/decompose and form a coating on another substrate. The process is carried out at elevated temperatures. The in-situ processing is a unique process in which chemical reaction results in the development of reinforcement in MMCs. The reinforcement can be formed from precipitations of the liquid of solid. The method provides the thermal compatibility between matrix and reinforcement, and surfaces are free of contaminations.
