Influence of material composition on formation of nano-interface for low friction in modtc oil

Recent years, the viscosity of motor oils gets lower in order to decrease resistance in the fluid lubrication region. On the other hands, friction in the boundary lubrication region increases, and this causes the possibility of seizure. In such circumstance, MoDTC is widely used as friction modifier to reduce friction in boundary lubrication. But it is well known that the low friction effect of MoDTC is depending on the conditions such as metal composition. So, it is required to understand the reason why metal composition affects reactivity of MoDTC. For this objective, we tried to appear the mechanism why tribo-film structure is different by metal composition. As a result of analysis of tribo-film structure on some kind metal substrate, the structure of low friction tribo-interface is clarified as follows; as the amount of Cr in metal substrate increases, the thickness of tribo-film is thinner. And Cr oxide exists at the interface between the Cr rich substrate and the tribo-film. So we considered that the oxidation of Cr affects the ease of decomposition of MoDTC and the thin film thickness, because Cr is easily to oxidize and Cr forms passive film. From this consideration, we made clear that making use of Cr rich metals can obtain low friction in MoDTC contained oil.