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

[Display omitted] •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.