A Review on Tribological Study of DLC Coatings in Combination with Bio Based Lubricants

In past few years DLC coatings and bio based lubricants have gained significant attraction due to their excellent tribological properties. Biolubricants showed synergetic behavior with contact surfaces, when used as a lubricant. Reason behind the attraction towards biolubricants is that they are renewable and biodegradable source of energy. The dominant properties of biolubricants are high flash point, less coefficient of friction, good wear resistance, high viscosity index, lower toxicity and high biodegradability. On the other hand, diamond like carbon (DLC) coatings have also gained attraction due to their excellent tribological properties which enables them to reduce the COF and wear of contact surfaces. In literature, many experimental studies have been carried out by researchers on DLC coating and biolubricants to analyze their interaction. Although biolubricants are not much applying in practical tribology fields but their properties are significant as compared to conventional synthetic lubricants. In this review paper, data from past few years published papers have been arranged in an organized manner to study the interaction of DLC coatings with biolubricants. Most widely used DLC coatings (W-DLC, a-C:H DLC, ta-C DLC) and biolubricants (palm oil, coconut oil, canola oil, sunflower oil, jatropha oil and rapeseed oil) were considered for this study. Tribological performance of symmetric (DLC) contacts and asymmetric (DLC and steel) contacts with biolubricants have been analyzed by comparing the average values of coefficient of friction and coefficient of wear. Synergetic behavior was obtained when biolubricants were used with symmetric DLC coated contact while tribological results were not much effective in case of asymmetrical contact of DLC coatings and steel.