The Progress of Special Lubricating Materials—A Brief Review

Lubricating materials generally include liquid and solid lubricants although in some cases gaseous lubricants are used.The types of lubricants could be divided into many classes based on the application environments or lubricants characteristics.Special lubricating materials mean the materials with properties superior to common lubricating materials.To enhance the lubricating performance via the design of molecular structure,bulk structure and the composite is always the main way to fabricate novel lubricating materials.For liquid lubricants and organic thin films,to design new molecular structure and reveal the tribochemistry mechanism are generally combined to develop novel lubricants.For example,the ionic liquids,as novel potential lubricants,are evaluated through different functional groups and tribochemistry during sliding process to guide the design and synthesis of ionic liquids with desired properties.The tribological performances of organic thin films heavily rely on their molecular structure and the film constructions.For typical solid lubricants,the design of bulk structure and composite are considered to be chosen to improve or adjust the frictional and wear resistance behaviors.The appearance of fullerene-like structure bestowed diamond-like carbon films much higher elasticity and much lower friction coefficient,while the introduction of metal elements reduced internal stress and improved the environment sensitivity in some cases.The blending and addition of inorganic nanoparticles are adopted to fabricate polymer lubricating materials with higher mechanical and wear resistance since it is not easy to design and fabricate novel polymers with desired lubricating properties.The development of high temperature lubricants is still a big challenge,in particular,lubricants with good consecutive lubricity from room temperature to high temperature(1 000 ℃ and higher).The addition of rare earth and ceramics,both with high temperature stability,to metal matrix is becoming a mainstream way to design and fabricate high temperature lubricants.The evaluation of lubricants could be done directly by the observation of friction and wear behaviors,which provide apparent judgment about the lubricants.The other way to get detail understanding about the lubricants applications is to see what happened on the surfaces during the sliding process,tribophysics and tribochemistry mechanisms,via the investigation of reaction products on the wear track,which in turn give some ideas or suggestion to adjust or design lubricants with desired properties.