Thermal spraying is a group of coating processes in which finely divided metallic or nonmetallic materials are deposited in a molten or semi-molten state to form a coating. The coating material may be a powder, ceramic rod, wire or molten material. A thermal spray procedure is used during the coating application.
The coating materials used to apply metal spray coatings are:
- Tungsten carbides
- Nickel-chrome carbides (chrome oxide, aluminum oxide, zirconia, titania)
Substrate materials include:
- Some plastics
Metal spray coating is also known as thermal spray coating.
A basic metal spray system consists of the following components:
- Spray gun - This is the primary device performing the melting and acceleration of the particles to be deposited.
- Feeder - Supplies the powder, wire or liquid to the torch.
- Media supply - Gases or liquids for the generation of the flame or plasma jet, gases for carrying the powder, etc.
- Robot - Manipulates the torch or the substrates to be coated.
- Power supply - Often a standalone power supply for the torch.
- Control console - Either integrated or a separate unit for all of the above components.
Metal spraying delivers coatings with an approximate thickness range of 20 micrometers to several millimeters, depending on the process and the feedstock. Coating materials available for thermal spraying include metals, alloys, ceramics, plastics and composites. Coating quality is usually assessed by measuring its porosity, oxide content, macro- and micro-hardness, bond strength and surface roughness.
Processes used to apply a metal spray coating:
- Plasma spraying
- Detonation spraying
- Arc wire spraying
- Flame spraying
- High velocity oxy-fuel coating spraying (HVOF)
- Warm spraying
- Cold spraying
Metal spraying is primarily used to produce coatings on structural materials. Such coatings provide protection against high temperatures, corrosion, erosion and wear. They can also change the appearance, electrical or biological properties of the surface.