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Fraunhofer Institute for Surface Engineering and Thin Films IST
 
Coating types    
 
Amorphous carbon films (DLC)
  As a group the amorphous carbon films are very varied. Coating properties can be adjusted within wide ranges by varying the hydrogen content and also by adding modifier elements.
 

Atomic structure of an amorphous, hydrogenous carbon coating (a-C:H).
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Amorphous, hydrogenous carbon coating (a-C:H): preparation of a fracture surface.
  This group is also commonly known as >diamond-like carbons< (DLC). This is due to the fact that some types of amorphous carbon films can have a very high diamond-like hardness of as much as 90 GPa (diamond itself is 100 GPa).

VDI guideline 2840 differentiates the following types of film:
  • Hydrogen-free amorphous carbon films,
    a-C
  • Tetrahedral, hydrogen-free amorphous carbon films,
    ta-C
  • Metal-containing, hydrogen-free amorphous carbon films,
    a-C:Me
  • Hydrogenous amorphous carbon films,
    a-C:H
  • Tetrahedral, hydrogenous amorphous carbon film s, ta-C:H
  • Metal-containing, hydrogenous amorphous carbon films,
    a-C:H:Me
  • Modified hydrogenous amorphous carbon films,
    a-C:H:X.
Amorphous carbon films are used in particular for tribological applications. As well as offering a high degree of wear protection they exhibit - in contrast to many ceramic hard films (such as TiN) - a very low coefficient of friction with respect to many materials. With steel, coefficients of friction of less than 0.05 are possible. Very good non-stick properties can also be obtained.
Another useful property is a modulus of elasticity which in comparison to hardness is relatively low - this is a good precondition for high film adhesion.

Applications are found in the following fields:
  • Wear protection - for example, for ball bearings
  • Friction reduction - for example, for machine elements
  • Non-stick function - for example, for forming tools
  • Biological applications in medical technology.
Amorphous carbon films are deposited by the PVD or PA CVD methods or combinations of them.

A bibliography for further reading is provided here.
 
 
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