Solid Lubricants of Combined Graphene and Iron Nanoparticles for Study of Friction and Stability

This
study focuses on designing solid lubricant particles by combining
graphene and iron nanoparticles (namely, graphene-iron (GI) particles)
and carrying out studies for behaviors of their lubrication for the
iron contact by molecular dynamics simulations. By the annealing process
of melting and cooling iron, we can create the lubricant particle,
where the iron nanoparticle tightly holds the graphene sheet. In the
sliding friction investigations, it is found that the influences of
orientation of the graphene sheets inside the contact, size and configuration
of the GI particles, and lubrication with the bare iron nanoparticles
on friction are strong at low pressure and very slight at high pressure.
The GI particles provide stability of the friction coefficient over
a wide range of pressure; however, it strongly increases with pressure
in the lubrication behaviors by the bare iron particles due to the
deformation of the particles. The iron contact in the presence of
the GI particles can achieve the ultralow values of the friction coefficient
from 0.009 to 0.042. The contact surfaces are not nearly damaged (slightly
elastic deformation) with the pressure up to 2.0 GPa. From the comparisons
between the results in this study and previous reports, the GI particles
have better lubrication than graphene coated on a surface and well
stabilize under pressure compared to the different lubricant nanoparticles.
The main reason for this is due to the contributions of graphene,
besides reduction of the contact area resulted from the configuration
of the nanoparticle, which promotes sliding and sharing of the pressure,
preventing collision between the lubricant particles.