Environmentally adaptive lubrication enabled by gradient structure design of TiN-MoS2/Ti

Abstract

Molybdenum disulfide (MoS2) films have been widely employed as lubricants for mechanical components but continue to face significant engineering challenges including their low hardness, high humidity sensitivity and weak adhesion to substrates. Although the co-deposition of MoS2 with additives provides enhanced functionality in some cases, the weak adhesion of MoS2 to the substrate is the key to the localized delamination or even early failure of the film. Herein, a novel MoS2-based film is designed and fabricated by magnetron sputtering deposition technique, which consists of Ti bonding layer, TiN load-carrying layer, TiN/Ti/MoS2 gradient layer, and top layer of Ti-doped MoS2 lubricating film. Results demonstrate that the rationally gradient design not only improves the adhesion strength between MoS2 and substrate, but also promotes the preferential growth of MoS2 along [001] zone axis perpendicular to the (002) crystal plane. The 3.2 at.% Ti-doped MoS2 film exhibits a low friction coefficient and wear rate before and after salt spray test, which is ascribed to the formation of a continuous and dense MoS2 tribofilm. Additionally, Ti additive can preferentially absorb oxygen in air, thereby preserving the self-lubricating ability of MoS2. This novel structure design provides an example for obtaining functional lubricants with good mechanical properties and environmental adaptability.