From Oxidative Wear to Carbon Transfer Film Lubrication: Revealing Load‐Induced Interfacial Evolution of a‐C:H Coatings on Ti6Al4V via Multiscale Characterization

The poor tribological performance of Ti6Al4V titanium alloy severely limits its application in moving components. Although hydrogenated diamond‐like carbon (a‐C:H) coatings can effectively improve their wear resistance, the mechanism underlying the load‐driven evolution of the friction interface remains unclear. This study systematically investigates the tribological behavior and interfacial dynamic evolution of a‐C:H coatings under different loads via multiscale characterization. Results show that the a‐C:H coatings significantly reduced the coefficient of friction (COF) and wear rate by 61.08% and four orders of magnitude, respectively. With increasing load, the COF decreased monotonically, while the wear rate first decreased and then increased, reaching an optimum at 10 N. Raman spectroscopy and transmission electron microscopy (TEM) analyses revealed that the load drove the evolution from a state dominated by iron oxides to a mixed phase and finally to the formation of continuous carbon transfer films. Critically, higher loads accelerate the formation rates of the carbon transfer film while promoting its graphitization, enabling rapid surface coverage that suppresses oxidative wear. This kinetic control facilitates the transition in the friction mechanism from oxidative wear to efficient shear lubrication by the carbon transfer film. This work establishes that the kinetic regulation of the interfacial pathway is the central mechanism through which load optimizes tribological performance, providing a foundational principle for the load‐adaptive design of surface coatings on titanium alloys.