Influence of Atomic Oxygen on the Vacuum Tribological Performance of MoS₂-Ti Composite Films Deposited by Unbalanced Magnetron Sputtering

MoS₂-Ti composite film with columnar microstructure was fabricated by unbalanced magnetron sputtering, and was irradiated by an atomic oxygen (AO) beam with 5eV kinetic energy and total fluence of 6.0×10²² atoms/cm². The MoS₂-Ti composite film exhibited a “blanket-like” surface morphology after AO irradiation. The MoS₂ phase on the film surface (within the depth of ~30 nm) and titanium suboxides (e.g. TiO_2-x, where 0<x<2) inside the film were oxidized by AO into MoO₃ and TiO₂, respectively, leaving the MoS₂ beneath the top 30 nm oxidation layer uninfluenced were oxidized to MoO₃ and TiO_2, leaving unchanged chemical state of element Mo in the film. After AO irradiation, initial friction coefficient and wear rate increased from 0.018 to 0.03 and 4.49 × 10⁻¹⁷ m³/(N·m) to 5.5 × 10⁻¹⁷ m³/(N·m), respectively, and its friction mechanism was transformed from adhesion to abrasion.