Atomic Scale Simulation Of Interfacial Properties And Mechanical Behavior Of Graphene/Titanium Matrix Composites

Titanium alloys have been widely used in aerospace and other fields because of their excellent properties such as high specific strength,good plasticity and high temperature resistance.But their properties need to be further improved.Graphene has excellent mechanical properties and is an ideal reinforcement phase for metal matrix composites.At present,there are some problems in the research of graphene/Ti matrix composites,such as serious interfacial reaction and unclear interfacial bonding mechanism.The first-principles can reveal the nature of interface bonding from the electronic and atomic scale,and molecular dynamics can simulate the mechanical behavior of interface at finite temperature.In this paper,the interfacial properties and mechanical behavior of graphene/Ti matrix composites were studied at atomic scale by first-principles calculation and molecular dynamics simulation respectively,which provided theoretical basis for the actual preparation of graphene/Ti matrix composites.In this paper,the interface adhesion work,interfacial energy,atomic structure and electronic structure of Ti/graphene/Ti interface are calculated by CASTEP software based on first-principles pseudopotential method.The stability of Ti/graphene/Ti interface and the tensile and shear deformation behavior at finite temperature are simulated by LAMMPS software based on molecular dynamics simulation method.The effects of defects,graphene layers and H atom on the interfacial properties and mechanical behavior of Ti/graphene/Ti were investigated.Based on（0001）_Ti（14）（14）（0001）_graphene,[21^—1^—0]_Ti（14）（14）[21^—1^—0]_graphene orientation relationship,two Ti/graphene/Ti interface models are established,and the second one is more stable.In Ti/graphene/Ti interface,the different interaction between top and center atoms results in the deviation of the atomic position distribution.Ti and C atoms have three different positions.In Ti/graphene/Ti interface,the bonding between Ti and C atoms has the characteristics of covalent bond and ion bond.The bonding between Ti and C atoms at the central position is stronger than that between Ti and C atoms at the top position.With the increase of graphene layers,the interface between Ti/graphene/Ti is more stable and binding is stronger,the displacement of Ti and C atoms decreases,and the binding between top Ti and C atoms is stronger than that between center Ti and C atoms.The introduction of vacancies in graphene strengthens the bonding of Ti/graphene/Ti interface,but at the same time the stability of the interface decreases.Ti atoms near the vacancies in graphene shift to vacancies,and have stronger ionic bonding with unsaturated C atoms near the vacancies.The direct bonding between H atom and unsaturated C atom in single vacancy graphene weakens the interface bonding of Ti/single vacancy graphene/Ti,but improves its stability.The solid solution of H atom in the octahedral gap of Ti weakens the bonding between Ti and strengthens the interface bonding,which is more stable.Ti/graphene/Ti interface can exist stably at 300K,800K and 1100K.Ti and Ti/graphene/Ti models exhibit plastic deformation along[1?100]with prismatic<a>slip,along[0001]with pyramidal<a+c>slip and along[11（?）0]with both prismatic<a>slip and pyramidal<a+c>slip.Pure Ti and Ti/graphene/Ti models exhibit the best mechanical properties when stretched along[11（?）0].During the tensile process,Ti atoms and C atoms at the interface keep good bonding before graphene breaks.It is difficult for the interface to deform during the tensile process,which hinders the dislocation slip and reduces the plasticity of the material.When pure Ti is sheared along[11（?）0],the twin deformation is induced by shear stress.There are two nucleation,growth and disappearance processes of twins during plastic deformation.When the Ti/graphene/Ti model is sheared along[11（?）0],the interface hinders the transfer of shear stress in the direction perpendicular to the interface.The plastic deformation is conducted by the formation and disappearance of stacking faults parallel to the interface,which makes the atoms move along the direction of shear.When pure Ti and Ti/graphene/Ti were stretched along[11（?）0]at800K,graphene still showed good reinforcing effect.When Ti/bilayer graphene/Ti is stretched along[11（?）0],graphene can warp and deform to relieve the stress in Ti.In the Ti/graphene/Ti model with preseted voids,the interface hinders the expansion of voids perpendicular to the interface and improves the deformation resistance of the material.