Graphitic Carbon Films Across Systems

When metal surfaces come into contact, lubricants are used to overcome friction. Various forms of hydrocarbons play a central role in lubrication, through both liquid lubricants and surface coatings. Solid lubricants like graphite and complex surface coatings such as diamond-like carbon have led to great advancements in friction mitigation. In addition to these designed carbon films, unintentional carbon films can also spontaneously form during metal–metal sliding. Here, we analyze various systems that produce carbon films, focusing on systems with cyclical metal sliding, hydrocarbon lubricants, and catalytic activity. The systems we analyze include friction polymers, diamond-like carbon coatings, varnish from industrial machines, metal-on-metal hip implants, microelectromechanical systems, and catalysis coke. These films, analyzed at the nanoscale, are primarily graphitic carbon with local regions of sp 2 bonding. The graphitic carbon can act as a lubricant in some systems and not in others. Through comparing these various fields, we seek to better understand the formation, evolution, and friction properties of carbon films. Through design and control of carbon films formation, we can control triboactivity to improve system performance.