Quantitative Evaluation on How Hydrogen-Content Affects the Atomic-Scale Adhesive Wear Behaviors of Hydrogenated Amorphous Carbon

Abstract Hydrogenated amorphous carbon (a-C:H) coatings exhibit excellent tribological properties, including low friction and high wear resistance, making them valuable for numerous engineering applications. However, under real service conditions, these coatings can still experience wear, limiting their long-term reliability. A clearer understanding of the underlying wear mechanisms is essential to improve their durability. The performance of a-C:H coatings is closely linked to their hydrogen content and atomic-scale structure. Following the two-step reaction theory proposed in our previous work [Adv. Sci, 2021, 8, 2002827], this study uses large-scale reactive molecular dynamics simulations to investigate how hydrogen content influences the activation energies (or energy barriers) of the two-step reaction: the interfacial bond formation and the interfacial-bond-induced atom removal. Results show that the activation energy of forming interfacial bonds rises with hydrogen content, because hydrogen passivates surface carbon atoms, reducing their reactivity; while the activation energy required to remove atoms remains largely unaffected by hydrogen content, since the number of bonds broken per removed atom stays nearly constant. These findings help clarify the relationship between the atomic structure of a-C:H coatings and their wear behavior, providing useful insight for designing more wear-resistant carbon coatings in the future.