High Temperature Induced Low Friction and Wear in a-C:Si via Formation of a “H Passivation Layer/a-SiO₂/H Passivation Layer” Structure in a Humid Environment

Doping Si into amorphous carbon can decrease humidity sensitivity, improve thermal stability, and retain excellent friction performance. Experimental studies have shown that Si-doped amorphous carbon formed Si-OH structures and frictional oxides in high-temperature and humid environments. However, the formation process of Si-OH and frictional oxides, as well as their structure, formation conditions, and antifriction properties, remains unclear. In this paper, reactive force field molecular dynamics (ReaxFF MD) was used to investigate the frictional performance of a-C and a-C:Si (7.2 atom %) at temperatures of 300, 700, and 1500 K in H₂O environments. The results showed that with increasing temperature, the friction force of a-C increases from 8.2 nN at 300 K to 15.51 nN at 1500 K, while that of a-C:Si decreases from 10.3 nN at 300 K to 5.6 nN at 1500 K. In H₂O environments, a-C:Si formed a "H passivation layer/a-SiO₂/H passivation layer" structure, which inhibited the formation of interfacial bonds between the upper and lower substrates and reduced the wear of the substrate while ensuring the antifriction and antiwear properties of a-SiO₂. This paper reveals the mechanism behind the low friction characteristics of a-C:Si in high-temperature and humid environments, providing theoretical guidance for the application of a-C:Si under such conditions.