What is metallization?
Metallization is a process where we apply different metallic and non-metallic materials to other surfaces. Metallization is most commonly used when we wish to protect the surface of an object against corrosion, wear, cavitation, and erosion. The process is recommended for the protection of steel surfaces that are exposed to external or environmental factors.
The definition of metallization in accordance with DIN standard 657  is: the application of thermal coating is carried out using special devices to liquefy or melt, spray and splash the coating material at high velocity onto a clean and pre-treated (primed) surface of the component.
This definition of thermal spraying is insufficiently descriptive; the basic operating principle of thermal spraying is melting the coating material inside the burner by electrical means. This liquid or semi-solid material is then sprayed and splashed by means of process gas onto the substrate, where it solidifies and forms a closed layer. Hereinafter are more detailed descriptions of certain aspects of these processes.
Which materials are suitable for metallization?
Any material can be used as the substrate, as long as its surface can be roughened by sandblasting; this means that any material whose hardness does not exceed 55 HRC can be used as the substrate. If the substrate is harder than 55 HRC thermal spraying can only be applied using more rigorous methods. As the adhesion is based mainly on mechanical joining, it is extremely important to carefully clean and pre-treat the substrate surface before thermal spraying. After the surface has been cleaned of dirt by mechanical or chemical means, the substrate is roughened by sandblasting using jets of dry corundum. Occasionally other agents may be used, such as chips of solid cast iron or steel beads. Besides the choice of blasting agents, other factors must be taken into account, for example the size and shape of the particles, the angle of the sandblasting jet, the pressure, and the cleanliness of the blasting agent. Using this method, the free surface energy is increased and the surface itself is activated; the increased surface area also enables the particles to better merge with the substrate.
Wire arc spraying
Wire arc spraying is a method where two metallic wires, usually of the same composition, are energetically charged, causing an arc to be generated between them. This arc in turn causes the wires to melt. Using spray gas, the molten feedstock is accelerated and applied to the substrate. By appropriately feeding the wire into the system, the arc can be continuously maintained. Suitable for this type of covering are primarily rotational symmetrical components, such as cylinders, shafts, discs and flat surfaces.
What are the advantages of metallization?
- Protection against corrosion.
- Protection against use-wear.
- Processing new parts
- Thermal and electrical insulation
- Possibility of subsequent thermal and electrical processing of the work piece
- Decorative purpose
- Protection against chemical factors
- Increased hardness and abrasion resistance of the material
- Provides conductive coatings on nonconductive materials.