Carbon layer

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Carbon layers are thin layers that mainly consist of the chemical element carbon . These include the plasma polymer layers , the amorphous carbon layers ( English diamond-like carbon , DLC), the CVD diamond layers and the graphite layers . With coatings made of carbon, a wide range of surface functions can be implemented, especially in the field of tribology , i.e. in applications subject to wear and tear.

Classification

Graphite layers

Graphite layers consist exclusively of sp 2 - hybridized carbon atoms. They are used, for example, on disc brakes on aircraft, as coatings for heating or fuel elements or, due to their biocompatibility , in many biomedical articles such as implants.

Diamond layers

Diamond layers are carbon layers with maximum hardness and maximum wear resistance. They can be produced using special chemical vapor deposition processes. This results in micro- or nano-crystalline layers that can be textured by changing the process parameters in a targeted manner and thus offer an extremely low coefficient of friction.

Amorphous carbon

Amorphous carbon is also known under the names DLC (diamond-like carbon) or diamond-like carbon.
The amorphous carbon layers are classified according to VDI 2840 and ISO 20523 as follows (with indication of the recommended abbreviation):

  • Hydrogen-free amorphous carbon layers , aC , mainly consist of sp 2 -hybridized bonds and are therefore also referred to as graphite-like carbon layers.
  • Tetrahedral, hydrogen-free amorphous carbon layers , ta-C , consist predominantly of sp 3 -hybridized bonds, which is why their mechanical properties are diamond-like.
  • Metal-containing hydrogen-free amorphous carbon layers , aC: Me
  • Amorphous carbon layers containing hydrogen, aC: H (H content> 35%)
  • Tetrahedral amorphous carbon layers containing hydrogen, ta-C: H (H content> 25%) with predominantly sp 3 -hybridized carbon atoms
  • Metal-containing hydrogen-containing amorphous carbon layers , aC: H: Me : By doping with metals, a composite is formed from an aC: H matrix and metal carbides . Layers made of this material have high wear resistance, low coefficients of friction and better adhesion of the layers. The material properties can be strongly influenced by changing the metal content.
  • Modified hydrogen-containing amorphous carbon layers , aC: H: X : By doping with elements such as Si, O, N, F and B, amorphous carbon layers can be heavily modified depending on the desired properties. Silicon, for example, increases the temperature resistance in an oxygen-containing environment. Doping with silicon and oxygen can greatly reduce the surface tension (up to values ​​in the order of magnitude of PTFE ). In addition, transparent and extremely scratch-resistant layers can be produced.

Applications

  • Amorphous carbon layers (DLC layers) are used, for example, in automotive engineering in internal combustion engines. Moving parts such as camshafts , piston rings and gears are coated with aC: H or aC: H: Me in order to minimize wear and friction and thus make vehicles more powerful and with fewer emissions.
  • Diamond-coated cutting tools for machining difficult-to-cut or highly abrasive materials such as graphite, ceramic and hard metal green parts, carbon fiber reinforced plastics.
  • Seals , for example mechanical seals for boiler feed pumps, are coated with amorphous carbon or diamond to minimize wear (electrical corrosion) and friction.

Manufacturing

The carbon layers are deposited using chemical (CVD) or physical ( PVD ) vapor deposition processes, usually in a vacuum . They are deposited as thin layers with a thickness of a few micrometers .

See also

literature

  • VDI guideline 2840: 2012-06 Carbon layers - basics, layer types, properties
  • Krause, A. et al .: Analysis of the friction behavior of DLC in warm bulk forming by using the ring compression test. In: Production Engineering, Vol. 9 (2015), no 1, pp. 41-49.
  • ISO 20523: 2017-09 Carbon based films - Classification and designations
  • DIN 4855: 2015-09 Carbon layers - DLC layers - Description of the layer architecture
  • DIN 4856: 2018-02 Carbon layers and other hard material layers - Rockwell penetrant test to assess adhesion

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