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.

本研究聚焦于通过将石墨烯与铁纳米颗粒复合，制备得到石墨烯-铁（graphene-iron，GI）固体润滑剂颗粒，并借助分子动力学模拟，开展其在铁基接触界面的润滑行为研究。通过对铁纳米颗粒实施熔融-冷却退火工艺，可获得该润滑剂颗粒，此时铁纳米颗粒可紧密包覆石墨烯片层。滑动摩擦研究结果表明：接触界面内石墨烯片层的取向、GI颗粒的尺寸与构型，以及采用纯铁纳米颗粒润滑等因素，在低压区间对摩擦行为的影响较为显著，而在高压区间的影响则极为微弱。GI颗粒可使摩擦系数在宽压力范围内保持稳定；而纯铁纳米颗粒润滑时，由于颗粒发生形变，摩擦系数会随压力升高而显著增大。采用GI颗粒润滑的铁基接触界面，可实现0.009至0.042的超低摩擦系数；当压力最高达2.0 GPa时，接触表面几乎无损伤，仅存在轻微的弹性形变。将本研究结果与既往文献报道对比可知，GI颗粒的润滑性能优于表面包覆石墨烯的润滑剂，且相较于其他类型的润滑纳米颗粒，其在压力载荷下具备更优异的结构稳定性。其核心原因在于：一方面，该颗粒的构型降低了接触面积，促进了压力传递与界面滑移，同时避免了润滑颗粒间的碰撞；另一方面石墨烯本身也贡献了关键的润滑作用。