High Temperature\nInduced Low Friction and Wear in\na‑C:Si via Formation of a “H Passivation Layer/a-SiO<sub>2</sub>/H Passivation Layer” Structure in a Humid Environment

Doping Si into amorphous carbon can decrease humidity\nsensitivity,\nimprove thermal stability, and retain excellent friction performance.\nExperimental studies have shown that Si-doped amorphous carbon formed\nSi–OH structures and frictional oxides in high-temperature\nand humid environments. However, the formation process of Si–OH\nand frictional oxides, as well as their structure, formation conditions,\nand antifriction properties, remains unclear. In this paper, reactive\nforce field molecular dynamics (ReaxFF MD) was used to investigate\nthe frictional performance of a-C and a-C:Si (7.2 atom %) at temperatures\nof 300, 700, and 1500 K in H<sub>2</sub>O environments. The results\nshowed that with increasing temperature, the friction force of a-C\nincreases from 8.2 nN at 300 K to 15.51 nN at 1500 K, while that of\na-C:Si decreases from 10.3 nN at 300 K to 5.6 nN at 1500 K. In H<sub>2</sub>O environments, a-C:Si formed a “H passivation layer/a-SiO<sub>2</sub>/H passivation layer” structure, which inhibited the\nformation of interfacial bonds between the upper and lower substrates\nand reduced the wear of the substrate while ensuring the antifriction\nand antiwear properties of a-SiO<sub>2</sub>. This paper reveals the\nmechanism behind the low friction characteristics of a-C:Si in high-temperature\nand humid environments, providing theoretical guidance for the application\nof a-C:Si under such conditions.