Friction condition switching two-type transfer layers of hydrogenated amorphous carbon with distinct tribological behaviors

Abstract

Hydrogenated diamond-like carbon (H-DLC) film exhibits excellent tribological properties in vacuum environments, making it highly suitable for applications in spacecraft motion systems. However, the lubrication performance and service life of H-DLC films are significantly affected by complex friction conditions, such as varying loads and motion modes (continuous or intermittent). This study investigates the tribological properties of H-DLC films under different friction conditions by altering contact stress, sliding mode, and contact frequency during friction tests against 440C steel balls. The results reveal two distinct types of transfer layers, shallow and dark, with differing tribological behaviors. Shallow transfer layers, formed under harsh conditions (high load, high contact frequency, and reciprocating sliding), exhibit high graphitization, leading to low friction coefficients but higher wear rates. In contrast, dark transfer layers, formed under milder conditions (low load, low contact frequency, and rotational sliding), show lower graphitization, resulting in higher friction coefficients but reduced wear rates. The formation of these transfer layers is influenced by the energy available to break sp³ carbon bonds at the friction interface, with high contact stress and alternating stress promoting graphitization and preventing debris accumulation. This study provides insights into the friction and wear mechanisms of H-DLC films and offers practical guidance for optimizing their performance in spacecraft moving parts by controlling friction conditions to achieve desired lubrication effects.