In about a decade, since interest about boundary lubrication properties of diamond-like carbon (DLC) coatings exists, mainly chemical aspects of the DLC lubrication were investigated, i.e. focusing on interactions between various additives and coatings, while physical aspects of coating-oil interactions were not discussed in a greater extent. To elucidate some of these effects, we have analyzed the friction behaviour of DLC coatings and steel under different boundary lubrication conditions by using polyalphaolefin (PAO) base oils having different viscosity grades. Based on this, we have identified several tribo-physical effects in these contacts and for the purposes of this paper we briefly discuss the physical adsorption between the oils and the DLC surfaces, clearly indicating existence of rather strong physically adsorbed layers, which were able to resist high shear stresses under severe boundary lubrication.

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