[SY-O4] Symposium O-4

[SY-O4] Effect of Tribochemical Reactions on Diamond-like Carbon and Wear under Water Lubrication: A Molecular Dynamics Simulation Investigation

^○Jing Zhang¹, Yang Wang¹, Jingxiang Xu¹, Yusuke Ootani¹, Nobuki Ozawa¹, Koshi Adachi², Momoji Kubo¹ (1.Inst. for Materials Research, Tohoku Univ., Japan, 2.Dept. of Mechanical Systems Engineering, Tohoku Univ., Japan)

Diamond-like carbon (DLC) coatings possess excellent frictional properties. However, the wear of DLC coatings is still a problem. To improve the properties of DLC, clarification of the wear mechanisms is required. It is reported that the wear of DLC under the water lubrication is lower than that in the air. To expound the wear mechanisms, clarification of this phenomenon is strongly demanded. However, the detailed mechanism is still unclear due to the complicated tribochemical reactions. Therefore, we studied the wear mechanisms of DLC under both vacuum and water environment by using the molecular dynamics method. The DLC model is made of two hemispherical substrates, to simulate real rough surfaces. The friction simulations were carried out by sliding two substrates. During the friction, under both environments the transfer of carbon atoms to their counter substrates was observed, indicating the adhesive wear of DLC. The number of transferred carbon atoms under vacuum condition was much larger than that under water lubrication, suggesting that the water environment suppresses the wear of DLC. Considering that interfacial C-C bonds which connect two DLC substrates promotes the transfer of carbon atoms, we investigated the number of interfacial C-C bonds. The number of interfacial C-C bonds under water lubrication was less than that in vacuum, indicating that the formation of the interfacial C-C bonds was suppressed by the water. To understand the cause of the suppression effect of water on the interfacial C-C bonds formation, we investigated the chemical reactions during friction process. With friction time going, the increase in the C-H and C-O bonds and the decrease in water molecules were observed, indicating the reaction between water molecules and carbon atoms. We suggest that these chemical reactions increase H and OH terminations on the DLC substrates and suppress the formation of the interfacial C-C bonds, and therefore the adhesive wear is inhibited.