Cryogenic vacuum tribological behavior and lubrication mechanisms of a-C:H films: Hardness-interface structure coupling

Diamond-like carbon (DLC) film, as a typical solid lubricant material, is expected to provide effective protection for moving components in extreme service environments of high vacuum and cryogenic temperatures. This work investigates the vacuum tribological performance and wear mechanisms of Cr/WC/a-C:H multilayer films from 25 °C down to −200 °C. The results show a non-monotonic trend: as the temperature decreases, both the friction coefficient and wear rate first decrease and then increase. The best performance occurs at −100 °C, with an average friction coefficient of 0.016 and an extremely low wear rate. Under cryogenic conditions, friction behavior is governed by the coupling between hardness and interfacial structure. At −100 °C, pronounced graphitization occurs at the interface, and abundant graphitic fragments in the wear debris contribute to low friction and wear. As the temperature decreases, the extreme hardness of the film causes severe wear of the Al 2 O 3 counterpart, and Al 2 O 3 debris induces third-body abrasive wear. This study provides a reference for material selection in cryogenic environments.