Diamondlike Carbon

Diamond-like carbon can be coated on a variety of substrates including metals (e.g. steel), polymers (e.g. teflon), and ceramics (e.g. glass). The coating provides certain diamond attributes, such as high wear resistance, low frictional coefficient, and extreme chemical inertness. There are different methods that may produce DLC, each with specific characteristics. Figure 10.1 shows the classification of DLC types based on the diamond-like bonding (sp3) and graphitic bonding (sp2) for carbon atoms, and also the content of hydrogen atoms.

A major compromise of DLC property is between hardness and adherence. In general, the more diamond properties (e.g. hardness) retained by DLC, the weaker is its adherence to the substrate. Figure 10.2 shows such a trade off (Sung, 2000).

Graphite (sp2) Hydrogen (H)

Figure 10.1. DLC's atomic structure and composition based on hydrogen content. a-D is amorphous diamond or tetrahedral amorphous carbon (taC). a-C is amorphous carbon or amorphous graphite.

Graphite (sp2) Hydrogen (H)

Figure 10.1. DLC's atomic structure and composition based on hydrogen content. a-D is amorphous diamond or tetrahedral amorphous carbon (taC). a-C is amorphous carbon or amorphous graphite.

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Figure 10.2. The inverse relationship between diamond properties of DLC and its coating merits.

Adherence, Smoothness, Slipperiness

Figure 10.2. The inverse relationship between diamond properties of DLC and its coating merits.

Figure 10.3. The ranking of various coating materials for hardness (a) and slipperiness (b).

DLC can be engineered to exhibit the unusual combination of hardness (wear resistance) and smoothness (slipperiness) (Sung, 2003). Figure 10.3 shows the comparisons of wear resistance and frictional coefficient for various coating materials.

Due to the exceptional properties of high wear resistance and low sliding resistance, DLC has been used for many tribological applications. Figure 10.4 shows some examples.

Figure 10.4. DLC coated products of razor blades (a), CD molds (b), and golf club heads (c).

Figure 10.4. DLC coated products of razor blades (a), CD molds (b), and golf club heads (c).

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