Friction and wear reduction via tuning nanoparticle shape under low humidity conditions: A nonequilibrium molecular dynamics simulation
JQ Shi and L Fang and K Sun, COMPUTATIONAL MATERIALS SCIENCE, 154, 499-507 (2018).
Because of the excellently thermal and chemical stabilities, nanoparticles have been considered as a potential lubricant additive to reduce friction and wear. In this study, nonequilibrium molecular dynamics simulations are used to reveal the friction and wear reduction mechanisms of diamond nanoparticle confined between the monocrystalline copper (Cu) slabs under low humidity conditions. The results indicate the movement pattern of nanoparticles can be changed from sliding to rolling by tuning the nanoparticle shape from a flat ellipsoid to a sphere. The sliding of sharp nanoparticles causes the water films being squeezed out from the worn region, which increases the surface friction and wear dominated by the polishing effect but impedes the formation of defects within Cu substrates. Contrarily, in the rolling process controlled by the rolling effect, a lot of water molecules remain in the worn region and thereby stop the surfaces from contacting with nanoparticles, which dramatically improves the friction and wear reduction. The interactive forces manifest the water films can transfer the normal force from slabs to nanoparticles during the rolling process. Therefore, by tuning the shape of nanoparticle additives to facilitate the rolling effect is helpful to reduce friction and wear in boundary or mixed lubrication.
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