Interfacial mechanical and tribochemical effects on friction mechanisms under air or vacuum conditions

Friction phenomenon is deeply affected by interfacial mechanical and tribo-chemical effects which contain major factors such as loads, sliding rates, sliding time, humidity, temperature and oxide films. For practical applications at different vacuum levels, friction mechanisms (adhesive wear, abrasive wear, fatigue wear, corrosive wear and micromotor wear) are of great importance to develop advanced materials with desirable tribological properties to promote vacuum tribology. In this review, combining current understanding of friction-wear interactions, the tribological phenomena caused by changes on the surfaces of friction pairs and highly dependent on the complex conditions in different vacuum environments are analyzed and summarized. Subsequently, protection strategies for different structural materials are summarized. Finally, this work provides the outlook for designing advanced and sustainable protective materials under different vacuum conditions.