Tribological Advantages of DLC (Diamond Like Carbon) coatings

The discovery of DLC materials stems from attempts to synthesize diamond in thin layers, which explains their misnomer of "Diamond Like Carbon" or "Adamantine Carbon". Indeed, their structure and properties are far removed from those of diamond. Nonetheless, it is a material with very interesting properties, particularly in terms of wear and friction. In the space of just a few decades, our understanding and mastery of DLC thin films has progressed enormously, and they have become reference materials in tribology, virtually indispensable for certain applications.

However, amorphous carbons are complex materials, and the use of DLC deposits requires a good understanding of tribological phenomena and the many influencing factors (load conditions, environment, atmosphere, temperature, etc.). Without these precautions, the unwary user will be surprised, as is often the case in tribology, by unexpected and potentially undesirable behavior.

As proof of this, the literature on friction tests on DLC provides friction coefficient values ranging from 0.001 to 0.7. This simple observation shows, on the one hand, the diversity of materials grouped together under the name DLC and, on the other, the extreme sensitivity of these materials to friction conditions.

As a result, it is impossible to give an exhaustive account of all the mechanisms involved in DLC friction and wear (transfer film, graphitization, role of adsorbed layers, etc.). Especially as these mechanisms are not all well understood and are still the subject of ongoing research.

Long regarded as costly deposits reserved for niche sectors such as motor racing, DLC is becoming increasingly accessible. They have, for example, become standard technological solutions for reducing friction in mass-produced car engines (cam/tappet, piston pin, etc.).

This article has been written to help manufacturers interested in this tribological solution. It provides a basic understanding of amorphous carbon thin films and their processing techniques. It also provides an overview of the various tribological phenomena involved in the friction of the many varieties of DLC, and makes potential users of these deposits aware of the influence of the parameters of the tribological system.