Structural Phase Transformation in Amorphous Molybdenum Disulfide during Friction
Yanbin Shi, Jibin Pu, Liping Wang
Abstract
Molybdenum disulfide (MoS2) coatings are known for their ultralow friction coefficient (0.005) due to the appearance of tribofilms with a lamellar structure. Nevertheless, the dynamics of MoS2 sheet formation are rarely studied. In this paper, temperature-, load-, and slippage-induced transition of pure MoS2 from an amorphous structure to a higher-order structure were studied by means of reactive molecular dynamics. The forming process of MoS2 flake conforms to the characteristics of classical nucleation theory (CNT). The relevant atomic-scale processes, such as nucleation, growth, approaching, aligning, and shaping, are analyzed and explained. The results confirm that the sliding process involved in friction does promote the formation of MoS2 tribofilms. In addition, the sliding behavior can facilitate the transformation of the crystal structure, which greatly reduces grain boundary defects in molybdenum disulfide flakes. Our findings may have important implications to gain insight into the crucial factors that contribute to rapid and effective structural transformation in friction processes.