Large-scale quantum molecular dynamics of water-lubricated diamond (111) surfaces in sliding contact reveals multiple friction regimes. While water starvation causes amorphization of the tribological interface, small traces of H<sub>2</sub>O are sufficient to preserve crystallinity. This can result in high friction due to cold welding via ether groups or in ultralow friction due to aromatic surface passivation triggered by tribo-induced Pandey reconstruction. At higher water coverage, Grotthuss-type diffusion and H<sub>2</sub>O dissociation yield dense H/OH surface passivation leading to another ultralow friction regime. Under lean water lubrication multiple collisions of asperities may lead to the formation of disorder graphene layers suggesting that super-low friction in carbon hard coatings are related to graphenisation of the top surface layer.

Friction regimes of water-lubricated diamond (111): Role of interfacial ether groups and tribo-induced aromatic surface reconstructions

255th National Meeting (2018)

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