Tribological interactions between DLC coatings and lubricants

In the last couple of years a tremendous research work has been done in the field of development and characterization of hard coatings, mainly to boost their use in machine component applications working under normal and extreme operating conditions. Generally, hard coatings improve tribological properties of contact surfaces under dry sliding, while under lubricated conditions their inertness hinder the possibility of boundary film formation. The aim of this paper is to elaborate on the interactions between diamond-like carbon (DLC) coatings and lubricants, and possible tribofilm formation in different tribological contacts. Therefore, relationships between surface properties (i.e. surface tension, surface free energy, contact angle) and tribological properties of the lubricated DLC coated contact, as well as the influence of oil additive type and concentration and contact conditions win be presented. It is believed that this type of knowledge will lead to further coatings modification in terms of improved tribological properties under boundary lubrication.