[SY-O7] Symposium O-7

[SY-O7] Influence of Tribo-Film Structure Generated from MoDTC at DLC/DLC Interface on Friction Behavior : A Molecular Dynamics Simulation

^○Masahiro Saito¹, Jingxiang Xu¹, Yusuke Ootani¹, Nobuki Ozawa¹, Koshi Adachi², Momoji Kubo¹ (1.Institute for Materials Research, Tohoku Univ., Japan, 2.Graduate School of Engineering, Tohoku Univ., Japan)

Diamond-like carbon (DLC) has excellent friction properties such as low friction and high wear resistance. Thus, it is used as a solid lubricant material for engine parts. For this application, it is expected that DLC is used with the MoDTC friction modifier. When MoDTC is used as additives, a tribo-film of MoS₂ layers is formed at a sliding interface during friction, leading to low friction. It is known that frictional property of this system depends on many factors such as composition of additives, a structure of DLC, and so on. Thus, to improve the friction property, it is required to understand effects of these factors on friction behavior of the tribo-film. However, the friction behavior is unknown because in situ observation of the sliding interface is difficult. Thus, in order to investigate the friction behavior, we performed molecular dynamics simulation by using reactive force field, which takes into account the chemical reactions. In this study, we analyzed the influence of the defects in the MoS₂ layers on friction behavior of DLC by using a DLC/MoS₂ layers/DLC model. Here, we investigated the influence of the defects by comparing the friction behavior of the MoS₂ layers with and without grain boundaries. The friction simulation of the model without grain boundaries shows that the DLC/MoS₂ interface is the sliding interface. On the other hand, the simulation of the model with grain boundaries shows that the MoS₂/MoS₂ interface is the sliding interface since C-S bonds is formed between DLC and MoS₂ around grain boundaries. In addition, the MoS₂ layers with grain boundaries show higher friction force because the sliding between the MoS₂ layers is inhibited when a grain boundary attacks another grain boundary in neighboring layers. Then, we found that these friction behaviors caused by grain boundaries in the MoS₂ are major factors that increase friction force in this system. We will report the influence of other defects at the conference.