Tribological Behavior Of Diamond-like Carbon Films In Water-based Environment

With the deterioration of the global climate and the increasing shortage of non-renewable energy,people's awareness of environmental protection is growing.It is of great significance to develop new water-based lubricants to reduce or even eliminate friction by using green,cheap and readily available water as a lubricating medium.It will also bring enormous environmental and economic well-beings to countries around the world.However,since the viscosity and pressure coefficient of the water itself are very low,the lubrication in the boundary lubrication state is insufficient,achieving hydrodynamic lubrication is more difficult,and the chemical reaction between water and metal parts will also cause corrosion.Therefore,in this paper,diamond-like carbon(DLC)films are deposited on the surface of 304 stainless steel by magnetron sputtering,and silica/graphene oxide and black phosphorus/graphene oxide nanocomposites as water-based lubricating additives are synthesized.The tribological behavior and synergistic lubrication mechanism of DLC film in pure water and the synthesized nanomaterial additives environment are discussed.The results show that:(1)The surface roughness of DLC films deposited on rough stainless steels will affect the tribological behavior in water environment.The smooth surface DLC film has an unstable friction coefficient when sliding against silicon nitride in water environment.Instead the DLC film with a rough surface shows very low frictional wear and a very long life.It is found that the excellent tribological properties of the rough DLC film are attributed to the boundary lubrication of the protective lubricating film produced by the tribo-chemical reaction.(2)The silica/graphene oxide nanocomposites synthesized by chemical grafting,which perfectly inherit the superior characteristics of two-dimensional layered nanomaterial graphene oxide and zero-dimensional nanoparticle silica.As water-based lubricant additive,it exhibits excellent lubricity of mixed-dimension nanocomposites.In addition to produce a very low friction coefficient at high contact pressures,the wear rate of the wear track,especially the ball,is greatly reduced,and the DLC film deposited on the steel substrate is protected from tearing.The excellent mechanical properties of graphene oxide nanosheets and the microscopic ballbearings effect of silica nanoparticles are the main lubrication and anti-wear mechanisms.(3)Black phosphorus/graphene oxide two-dimensional layered nanocomposites are successfully synthesized by self-assembly of black phosphorus,which synthesized by improved liquid phase stripping method,and two-dimensional layered nanomaterial graphene oxide.As water-based additive,the nanocomposites exhibit superior lubricating properties as compared with single black phosphorus and graphene oxide.The water molecules adsorbed on the surface and penetrated in the inter-layers and the microscopic two-dimensional heterogeneous layered structure of the nanocomposites significantly reduce the interlaminar shear force,resulting low friction behavior of DLC in an aqueous environment.