Impact of Extreme Conditions of High Load-Speed Coupling on the Friction Behavior and Microscopic Mechanism of DLC Films in CO₂ Fracturing Environments

In the CO2 fracturing environment, although diamond-like carbon (DLC) films have high hardness and ultralow friction, the lack of systematic understanding of micromechanisms like interfacial chemical reactions and atomic migration under high-load and high-speed coupling extreme conditions restricts the optimization of DLC films on fracturing pump plungers. This study overcomes the spatiotemporal resolution limitations of conventional experimental methods. It innovatively builds a reactive molecular dynamics model with CO2 fracturing fluid to analyze the atomic-scale dynamic behavior and mechanisms at frictional interfaces in fracturing environments. The findings show that increasing sliding speed reduces contact and reaction time, causing smaller atomic displacements on the Fe block surface and lowering friction and wear. Conversely, higher loads enlarge the contact area, boost adhesion of iron compounds, and increase atomic displacement, intensifying friction and wear. In addition, the study innovatively identifies a dynamic equilibrium critical point at high speeds and loads. It also reveals the cross-scale coupling mechanism of interfacial dynamic passivation and lattice reconstruction under extreme working conditions. This work provides a theoretical basis for creating "construction parameters-fracturing environment" codesign criteria for DLC coatings on fracturing pumps. It is highly important for prolonging plunger life and enhancing fracturing efficiency.