Study On The Effect Of Graphene Coating On Properties Of Aluminum In Indentation And Scratch

In conventional metals,aluminum has heat resistance,mechanical properties,electrical properties and corrosion resistance,which makes it of great significance in many industrial applications.However,due to the inherent softness of aluminum,its poor resistance to invasion and friction limit its potential application.Graphene has the advantages of high strength,light weight and large surface area,so it can be used as a new lubricating additive to protect and enhance the surface properties of aluminum,reduce its friction loss,and improve the application range of aluminum materials in industry.Therefore,In this paper,the mechanical properties of graphene-coated aluminum materials were studied from nano indentation and nano scratches by molecular dynamics method.The first part is nanoindentation simulation.First of all,the indentation simulation models of single crystal aluminum(Al)and single and double graphene coated aluminum(Gr/Al)were established.The indentation properties of Al under spherical indenter were studied,and the indentation mechanical behavior was analyzed.At the same time,the Gr/Al was simulated under the same conditions to explore the effect of Gr coating on the properties of Al substrate under indentation.The results show that Gr coating can significantly enhance the loading capacity of Al,delay the beginning of plastic behavior of Al,and improve the contact stiffness and elastic capacity.Afterwards,through the analysis of the material deformation behavior and internal stress in the indentation process,it is found that the in-plane tensile stress of Gr has a great resistance to the movement of the indenter,and the Gr coating expands the bearing range of Al,so that more Al atoms participate in the force,which improves the bearing capacity of the matrix.It can be seen that the main reason for Gr to improve the indentation properties of Al is the "lifting effect" of Gr coating itself and the substantial increase of the bearing area of Al.In the next part,through the analysis of the internal dislocation propagation in the indentation process,it is found that the Gr coating makes the dislocation in Al which should have expanded to the free surface diffuse to the internal of the material,so that a large number of dislocation atoms fill the whole matrix.It can be seen that another main reasons why Gr improves the indentation properties of Al is that Gr coating changes the movement mechanism of dislocations in Al.In the end,by comparing the indentation properties of Al under single and double Gr coatings,it is found that increasing the number of Gr layers can improve the bearing capacity of the whole system,but reduce the critical depth of the system.The second part is nano scratch simulation.First of all,the scratch simulation models of single crystal aluminum(Al)and single and double graphene coated aluminum(Gr/Al)were established,and the nano scratch simulation of Al and Gr/Al was carried out under the same conditions to explore the effect of Gr coating on the properties of Al substrate under the effect of scratch.The results show that the addition of Gr coating can greatly reduce the friction coefficient of Al and significantly improve its friction performance.At the same time,it is found that Gr chirality has little effect on the friction performance.Afterwards,through the analysis of the variation of indentation force and scratch force with the scratch length in the stable stage of scratch,it is found that Gr coating can not directly reduce the friction,but can improve the friction performance by greatly improving the bearing capacity of the material to the normal force.In the next part,through the analysis and summary of the normal force,friction and friction coefficient of the two kinds of matrix under different indentation depth,it is found that the normal force of Gr/Al shows obvious linear characteristics on the indentation depth,while the normal force of Al is not sensitive to the change of indentation depth,and the friction and friction coefficient of the two kinds of matrix have a certain linear relationship with the indentation depth.In the end,by comparing the friction properties of Al under single and double Gr coatings,it is found that double Gr coating can further reduce the friction coefficient,but increasing the number of Gr layers can not directly reduce the friction of the substrate,but has the same strengthening mechanism as Gr coating enhancing the scratch properties of Al.