| Flame spraying | Plasma coating
Coating processes apply a fixed layer on a workpiece or substrate. According to the status of the coating material during the application on differentiates after:
1) Application from the gaseous or vaporous state (e.g. vacuum evaporation, metallization, plastic metallization, vacuum web coating). Here the CVD-procedure (chemical vapour deposition) should be mentioned, where such metals can be applied, if suitable gaseous compounds such as chlorides or fluorides exist. According to this the evaporation of hard material layers from titanium carbide is possible after the following reaction: TiCl + CH4 +nH2 ---> TiC + 4HCl + nH2 (temperature approx. 1000°C). Other hard material coatings produced in this procedure are VC, SiC, W2C, TiN, Si3N4, HfN, TiB2 and Al2O3. Due to the high temperatures only ceramics, but no steel can be coated by this method. With the PVD-procedure (physical vapour deposition) coatings are applied at lower temperatures (up to 300°C) in vacuum (ion plating) or sputtered. This process is suitable for steel.
2) Application of liquids or materials in the form of paste (e.g by brushing, dipping, painting). In this category we also find coatings, in which refractory fillers are suspended in a carrier liquid.
3) Application from the ionized status by (e. g. galvanizing , eloxal process, electrophoretic coating),
4) Application from the granular or powdered status (e.g. powder coating, flame spraying, plasma spraying). Here the powdered coating material is brought into a flamme by the use of a carrier gas and partly melted prior to application on the substrate.
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