Fabrication And Cutting Performance Of Graphene Reinforced Al₂O₃ Based Ceramic Cutting Tool

Alumina based ceramic tool material has incomparable advantages comparing with carbide tool materials in high speed cutting for its good mechanical properties,such as high hardness,good chemical stability,high heat resistance and high wear resistance.However its strength,fracture toughness,thermal conductivity and thermal shock resistance are relatively low,which limits its wide application in high speed cutting.Graphene is a one atom thick and closely packed two-dimensional lattice,and has super specific surface area,super high strength and toughness,and provides new ways and principles for reinforcing ceramic tool materials.The feasibility of interface control by introducing graphene was determinded by the first priciples firstly,then based on the microstructure of ceramic tool materials,the influence of microstructure on macro mechanical properties is studied.Furthermore,the results were used to guiding the design of graphene reforced ceramic tool materials.In the end,the graphene reforced Alumina/Titanium carbide ceramic tool materials were fabricated and the cutting performances had been studied.The crystal structure model of Alumina,Titanium carbide and graphene were build and optimized,and the crystal surfaces were cutted based on the optimal structure,then the properties and stability of the crystal surfaces were calculated and analyzed to obtain the most stable surface.In the end the interfaces were build and calculated using the first principles.The surfaces of alumina crystal and titanium carbide crystal surface are stable,and no surface reconstruction was occurred,and the most stable surface are Al2O3(0001)? Ti termination TiC(111)respectively.The energy of interface with graphene is lower than others.The higher the interface energy,the greater the bonding strength of the interface is.It is indicated that graphene could reduce the interfacial strength of composite materials and form weak bonding interface with other components of ceramic tool materials.So It is feasible to control the interface by graphene.The microstructure FEM model of ceramic tool materials was build and the influence of the cohesive element stiffness and grain diameter on crack propagation was studied.The model parameters corresponding to the brittle fracture process of ceramic materials were determined,and the result of simulation is agree well with experiment.The microstructure model with graphene and prediction model of material properties were bulid,and the ratio of graphene interface and volume ratio of ceramic components were given by analyzing the influence of components strength,volume ratio,grain diameter and graphene content on flexural strength and fracture toughness.It has obvious reinforcing effect as the ratio of graphene interface is 15%.The material has the best macroscopic mechanical properties when the volume ratio of Al2O3 and TiC is 7:3.The graphene reinforced A12O3/TiC ceramic tool materials were fabricated by HP,The addition of graphene is determined by optimization,and the reinforcing mechanisms of graphene were analyzed.The TEM was used to observe the interface and the interfacial differential electron density was calculated.Compared with the material without graphene,the flexural strength and fracture toughness were improved 30%and 23%as the graphene content was 0.2 wt%.The degree of crack deflection iand the frequency of crack branching all increase because of the addition of graphene.Besides crack deflection and branching,graphene pullout and bridging,crack blunting and transgranular fracture,graphene also introduced synergistic toughening mechanism of strong and weak interfaces,which achieved the uniformity of machinability and strength and toughness of ceramics.The weak bonding interface inspired microcrack toughening mechanism and brought the control of interface;The microstructures in HP direction and vertical direction are different because of graphene,as a result,the properties of cutting tool are anisotropy.The cutting performance of the graphene reinforced Al2O3/TiC ceramic tools when continuous turning 42CrMo was investigated.The wear resistance of the cutter is obviously increased by gaphene.The main failure mode is the adhesive wear ont the flank and a little ruin in the blade.The rake face failure was not observed at the the medium and low cutting speed(100-200m/min),and it is indicated that graphene could inhibit crack initiation and expansion.The optimal cutting speed is about 200m/min,and under the speed,the tool life of ATS2 is higher than commercial cutters CC650.