The development of modern engines involves the use of new materials such as diamond-like carbon (DLC) coatings. As these coatings possess different mechanical and physical characteristics to steel, investigation of their friction and wear properties when rubbing against a steel counterpart in a lubricated environment is needed. Specific tests were used to assess the tribological behaviour of these new surfaces (specifically an undoped DLC and a chromium-doped DLC coating). Chemical analyses were also performed in order to evaluate the reactivity of the formulated oil on the various surfaces. The results of the present work clearly show that there was no evidence of tribochemical reaction on DLC coatings. Anti-wear additives were still reacting on the steel counterpart for the undoped DLC case, resulting in better wear properties for the coating. The addition of a metal to the amorphous carbon matrix led to an improvement in wear but inhibited/removed the anti-wear film on the steel counterpart.

High-performance coatings are currently used in automotive racing engine applications and are being considered for commercial fleet applications. Because crankcase lubricants were designed for steel surfaces, the change to these new materials may result in different boundary lubrication mechanisms. The aim of the present study is to investigate the friction and wear properties of a series of commercial coatings using simple component-blend lubricants as well as commercial lubricant formulations. The tribological testing revealed that some of the commercial coatings possess advantageous friction and wear properties when compared with steel. The study also stresses that in many cases the use of these coatings results in increasing wear on the steel counterpart.