In situ friction-induced amorphous carbon or graphene at sliding interfaces: Effect of loads.

• The lubricity of ethylene glycol under high load was well investigated. • Graphene was induced to form by tribochemical reactions. • The graphene lubrication mechanism was attributed to high flash temperature and catalysts. Loads were always treated as a key factor for alcohols lubrication, low loads such as 1 to 3 N made the tribosystems achieve the superlubricity assigning for tribochemical reactions. In this work, tribochemical reactions still exhibited the important role in alcohols lubrication. High loads such as 98 and 196 N could induce the formation of amorphous carbon and graphene respectively, which both made the tribosystems achieve the superior wear-resistance. Graphene could effectively keep the stable friction coefficient compared to amorphous carbon. First-principles calculations showed that ethylene glycol was easily dissociated to ethylene on WC surface. TEM analysis exhibited the chain-like amorphous carbon for sliding at 98 N, which indicated the polymerization products of ethylene. When increasing the load to 196 N, amorphous carbon was further transformed to graphene. [ABSTRACT FROM AUTHOR]