Effect Of Rolling Process On Microstructure And Mechanical Properties Of GNPs/Ti Composites

Titanium matrix composite is considered as a promising material which has light weight and high strength.It has been considered to be used in the filed of aerospace.Graphene is an ideal reinforcement for metal matrix composites which has high elastic modulus,high fracture strength,extreme thermal conductivity and super charge-carrier mobility.However,the main troubles are the agglomeration of graphene and the interfacial bonding between graphene and metal matrix.In this paper,large plastic deformation(rolling process)was used to solve the problems of the agglomeration and the interfacial bonding.The microstructural evolution of GNPs(Graphene Nanoplatelets)/Ti composites during the rolling process and the effects of rolling parameters on the microstructure and properties of GNPs/Ti composites was studied.The microstructural evolution of GNPs/Ti composite during the rolling process was invesgated.After the preparation of GNPs/Ti composites and pure Ti by mechanical balling and spark plasma sintering(SPS),the tests of three rolling passes were established.The microstructural evolution of GNPs/Ti composites and pure Ti after each pass was analyzed by optical microscopy(OM),scanning electron microscopy(SEM)and electron back scattered diffraction(EBSD),and mechanical properties were characterized.Under the same rolling conditions,the matrix grains of GNPs/Ti composites were obviously smaller than that of pure Ti grains and the fiber structure was more obvious.It indicated that the addition of GNPs prevented the growth of the matrix grains and promoted the deformation of matrix grains along the rolling direction.During the rolling process,agglomerated GNPs were dispersed and cutted,and GNPs were broken.The ultimate tensile strength of the composites with 60%rolling reduction is 680 MPa,which is increased by 24%compared with pure Ti.In order to study the effect of reduction on the microstructure and properties of GNPs/Ti matrix composites,as-sintered GNPs/Ti composites were rolled with reduction of 50%,60%,70%and 80%respectively.Through the observation of four different reductions,it was found that with the increase of reduction,nucleus amount of dynamic recrystallization increased,more grains were refined,and the orientation of GNPs along the rolling direction became more and more obvious.The agglomerated GNPs clusters were dispersed,the size of GNPs was reduced and the transverse texture was more and more strong.When the degree of deformation reached 80%,there were strong((?)41)[(?)9(?)8] and ((?)24)[03(?)1]textures in GNPs/Ti composites.The tensile strength of GNPs/Ti composites first increased and then decreased with the increase of reduction,reached a maximum of 704 MPa.The fracture elongation of the GNPs/Ti composites decreased with the increase of reduction.The dynamic strength of GNPs/Ti composites with four different reductions in the normal direction and rolling direction increased with the increase of strain rate.The dynamic strength of GNPs/Ti composites with 50%deformation reached 1419 MPa,dynamic strain was 29.8%.The effects of GNPs,Orowan strengthening and grain refinement on the fracture strength of GNPs/Ti matrix composites at room temperature were investigated by means of simulation.The mechanical properties of GNPs/Ti composites show that the bearing loads of GNPs is the main strengthening mechanism of GNPs/Ti composites.The rotation of GNPs can increase the fracture strength of GNPs/Ti composites.The grain refinement enhances the fracture strength of GNPs/Ti composites a little.The effect of rolling pass on the microstructure and properties of GNPs/Ti composites was studied,and the annealing process of GNPs/Ti composites was also explored.The GNPs/Ti composites were rolled with 2,3,4,5 passes.As the number of passes increased,the more nucleus amount of dynamic recrystallization,the strength of transverse texture decreased,and twins were more activated to meet the coordination deformation,and the damage degree of GNPs was higher.The rolling pass had a little effect on the tensile strength of GNPs/Ti composites,and the plasticity firstly increased and then decreased.Three annealing processes with different annealing temperatures were designed for four rolling passes of 70%reduction of GNPs/Ti composites.The microstructure and mechanical properties of the obtained GNPs/Ti composites were compared and it was found that with the increase of annealing temperature,the twins disappeared,small recrystallized grains increased.The elongation of the annealed GNPs/Ti composites significantly improved than the composite without annealing,the tensile strength decreased.