Friction Regimes of Water-Lubricated Diamond (111): Role of Interfacial Ether Groups and Tribo-Induced Aromatic Surface Reconstructions

Abstract

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 H_{2}O traces 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_{2}O dissociation yield dense H/OH surface passivation leading to another ultralow friction regime.

Role of microstructure and structural disorder on tribological properties of polycrystalline diamond films

“…Apart from the above, recent studies demonstrate the importance of surface chemistry and tribological environment on the nature of friction and wear [8,12,188,19]. For example, in a humid atmosphere, friction and wear of diamond and tetrahedral amorphous carbon films are significantly reduced due to surface passivation and chemical rehybridization of sp 3 to sp 2 bonding [8,12,18,20,21]. Further, CoF on diamond coatings reduces with decrease in surface roughness as reported by several groups [22,23,24].…”

“…Diamond is an indispensable material in mechanical and tribological applications because of its combined characteristics of extreme hardness and ultralow friction. Typically, the coefficient of friction (CoF) of polycrystalline diamond films ranges between high to ultralow value depending upon tribo test conditions [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Some of the parameters affecting the tribological properties of diamond are contact pressure, crystallographic orientation, counterbody and surface roughness of the film [13,14,15,16].…”

“…Some of the parameters affecting the tribological properties of diamond are contact pressure, crystallographic orientation, counterbody and surface roughness of the film [13,14,15,16]. More importantly, tribofilm formation is one of the critical mechanisms to explain the ultralow friction and wear on diamond films [2,17,18].…”

“…It is also noted here that the as grown diamond is always terminated with large amount of -H which can also participate on reduction of CoF on diamond. Furthermore, Kuwahara et al[18] observe different regimes of friction on diamond (111) varying from very high to superlubricity as a function of water molecules in the tribo-envirnment. The most important observation is that an aromatic passivation of surface via Pandey surface reconstruction occurs with a sufficient amount of water molecules that can lead to formation of graphene nanostructures on diamond and amorphous carbon surfaces [188].…”

Enhancement in the tribological properties of Cr/DLC multilayers in methane: structural transformation induced by sliding

“…The prevailing views about repassivation mechanisms are chemical termination and rehybridization. Chemical termination has been proved by experiments and simulations [26][27][28]. For example, DLC film exhibited lower wear and friction under humid environments than under vacuum or dry gas [29].…”