First-principle Calculations Of The Interfacial Adhesion In Nano-carbon Materials Reinforced Mg-based Composites

Because of their excellent properties such as high specific strength,specific stiffness,specific modulus and light weight,magnesium matrix composites are considered as one of the most efficient ways to improve the mechanical properties and industrial application of magnesium alloys.Nanocarbon materials(graphene,carbon nanotubes,etc.)have excellent mechanical properties such as high strength and high modulus,and are often used as the reinforcement of magnesium matrix composites.However,it is difficult to produce stable interfacial binding between carbon nanoreinforcement and magnesium matrix.By introducing MgO nanoparticles as intermediates,the interfacial bonding strength between magnesium matrix and carbon nanocomposites can be significantly enhanced.In this paper,the first-principles calculation is adopted to study the binding properties of Mg/MgO,MgO/graphene and Mg/graphene interface structures,which can clarify the bridging mechanism of MgO between the magnesium matrix and carbon nanoreinforcement at atomic scale.The results can provide guidance for the design of magnesium matrix composites and accelerate the development of new magnesium alloy.The main research contents are as follows:1.By taking bulk calculations for Mg and MgO crystal,we compared the results with the experimental data to verify the reliability of the calculation method.Then,the surface of Mg(0001)and MgO(1-11)were cleaved to research the surface convergence and stability.Thus we can ensure the number of atomic layers for surface structure which reflect bulk properties.According to different surface terminal and different atomic alignment in interface,Mg(0001)/MgO(1-11)interface with six different structures were established(o-top,o-hcp and o-fcc types with O-terminal and mg-top,mg-hcp,mg-fcc structures with Mg-terminal).The optimal interface separation and the corresponding work of separation were obtained through the fitting curves of the relationship between the interface separation and the interface work of separation.It is found that O terminating Mg(0001)/MgO(1-11)interfaces have higher work of separation than that of Mg terminating structure,which means tighter interface bonding.The study of electronic properties shows that the interfacial interaction in O terminating structures is the combination of ionic bond and weak covalent bond,while for Mg terminating structure is mainly metal bond.That is the reason for the difference in the macroscopic interface bonding strength between interfaces with two different terminations.2.Based on the calculation of lattice mismatch,the MgO(1-11)and the graphene surface were expanded to form a coherent interface.Due to the different atomic alignment at the terminals and interfaces,there are four different structures in the MgO(1-11)/graphene interface:OTH and OB types with O-terminated MgO(1-11)surfaces and MTH,MB types with Mg terminals.The interfacial work of separation is calculated by UBER method and geometric optimization method.It is found that the O terminating MgO(1-11)surface is more likely to produce a stable combination with graphene than that of Mg terminating type.From the study of electronic properties such as charge density and density of state,it can be seen that at the interface of OTH structure,there are obvious charge accumulation between top site O atoms and corresponding C atoms.Which means that top site O atoms can break the sp~2 bond in the corresponding graphene layer and formed a strong covalent bond with aligned C atoms.This results in a tight interface between the MgO(1-11)surface and graphene.3.Due to the great difference in lattice parameters between Mg(0001)and graphene,a large surface supercell was established to make the two surface structures match each other.Therefore,only one Mg(0001)/graphene interface containing top,hollow and bridge alignment was built in this work.For reference,the work of separation for all interface structures in this paper was calculated,and it was found that the order of interface binding strength of the three interfaces obtained by UBER fitting was:Mg(0001)/MgO(1-11)>MgO(1-11)/graphene>Mg(0001)/graphene.While after sufficient geometric relaxation,the work of separation of OTH type MgO(1-11)/graphene interface increased from 0.93J/m~2 to 4.70J/m~2,which even exceed that of Mg terminated Mg(0001)/MgO(1-11)interface.This indicates that under certain terminal and alignment mode,MgO(1-11)surface can bond with graphene to form a tight interface.The research of charge density show that only weak?bond could be found between Mg(0001)and graphene,which is the reason for the poor interface binding performance of Mg(0001)/graphene.The researches in this paper show that it is difficult to form a stable interface between nano-carbon materials and Mg matrix.While by introducing MgO,the O-terminate MgO(1-11)surface could form tight interface with either Mg(0001)or graphene.It is proved that MgO can truly play a fine bridging role between magnesium matrix and carbon nanoreinforcement.