Research On Al₂O₃@RGO Core-Shell Ceramic Tool And Its Cutting Performance

Graphene has long been regarded as an ideal reinforcement for ceramic composites due to its outstanding physical and mechanical properties.However,the van der Waals forces and the large ?-? forces between graphene sheets make it easy to stack and agaggregate in ceramic materials,which seriously weakens its enhancement effect on ceramic materials.In view of the difficulty of uniform dispersion of graphene in ceramic materials and the difficulty of forming a good contact interface between it and ceramic materials,this topic selected the hummers method to prepare negatively charged graphene oxide(GO)with a large number of oxygen-containing functional groups.On the basis,the electrostatic force between the positively charged nano alumina(Al2O3)powder modified by the surface of the silane coupling agent and the GO makes the GO uniformly adsorbed on the surface of the nano Al2O3,and the graphene-encapsulated alumina(Al2O3@RGO)core-shell composite powder was obtained by high temperature reduction.In this paper,Al2O3/TiC and Al2O3/TiB2 were used as the matrix to prepare Al2O3@RGO core-shell ceramic tool materials by the hot press sintering(HP)process,and the relationship between the microstructure and mechanical properties was investigated.Under the same sintering process parameters,the in-situ reduced graphene oxide(RGO)reinforced ceramic tool material is prepared with GO as the starting nano-additive phase,which is combined with the ceramic tool material added with Al2O3@RGO core-shell composite powder.In contrast,the effect of graphene addition on the dispersion level of graphene in ceramic tool materials and the bonding strength of the interface between it and ceramic tool materials was studied,and the microscopic effect of Al2O3@RGO core-shell composite powder on ceramic tool materials was revealed.The mechanism and influence law of structure,related mechanical properties,friction and wear properties and cutting performance.The relevant contents and conclusions of this research are as follows:(1)The design idea and principle of preparing core-shell composite powder of graphene-coated nanoparticles and using it as nanometer additive phase to prepare coreshell ceramic tool materials with excellent mechanical properties were proposed,and the corresponding tool design model was established and the corresponding calculation was carried out.On this basis,with the requirements of the design of nano-ceramic tool materials as a reference,the design of ceramic tool material components and preparation technology and other related factors as a starting point,the tool material composition system was selected,and the physicochemical compatibility between the components of the tool materials was analyzed.(2)With cheap silane coupling agent as organic self-assembly medium,the simple electrostatic self-assembly method is applied to make the charge attraction between negatively charged GO and positively charged nano-alumina particles modified by silane coupling agent successfully combine nano-alumina particles with GO.The graphene coated nano-alumina(A12O3@RGO)core-shell composite powder was further prepared by high temperature reduction.At the same time,its self-assembly mechanism and synthesis conditions were carried out.The microstructure and phase composition were analyzed and characterized by XRD,Raman,FTIR,TAG,SEM,XPS,TEM and other testing techniques.The research results show that the graphene is uniformly and densely coated on the surface of the nano-Al2O3 particles,and forms a strong interface bond with the nano-Al2O3 particles.(3)Al2O3/TiC and Al2O3/TiB2 were used as matrix materials to prepare Al2O3@RGO core-shell ceramic tool materials by hot-pressing sintering process,and the relationship between their microstructure and mechanical properties was investigated.Under the same sintering process parameters,GO was selected as the initial nano additive phase to realize the preparation of in-situ reduced GO enhanced ceramic tool materials.By comparing it with the ceramic tool materials added with Al2O3@RGO core-shell composite powder,when the content of Al2O3@RGO coreshell composite powder in ceramic tool material is different,the influence of its mechanical properties and microstructure is studied.The results of the study show that:when 3.0 vol.%Al2O3@RGO core-shell composite powder is added,the overall mechanical properties of ATC-G@3.0 tool material are the best,with a hardness of 19.52 GPa,a bending strength of 1063.52 MPa,and a fracture toughness of 9.16 MPa·m 1/2.Compared with the atC-G3.0 tool material with 3.0 Vol.%GO,it is increased by 16.82%,27.92%,26.87%respectively.When 3.0 vol.%Al2O3@RGO core-shell composite powder is added,the overall mechanical properties of ATBG@3.0 tool material are the best,with fracture toughness of 8.42 MPa·m1/2,hardness of 21.19 GPa and bending strength of 998.69 MPa.Compared with ATB-G3.0 tool material with 3.0 vol.%GO,the cutting tool material increases by 26.61%,16.11%and 35.46%,respectively.By analyzing the microstructure of ceramic tool material,it can be seen that the addition of Al2O3@RGO core-shell composite powder can effectively improve the dispersion level of graphene in ceramic tool material and the strength of interface bonding between it and ceramic tool material,thus further enhancing the mechanical properties of ceramic tool material as a whole.(4)The friction and wear properties of Al2O3@RGO core-shell ceramic tool materials prepared by hot pressing sintering were studied through the friction and wear test system.This chapter mainly takes normal load and sliding speed as variables,and chooses to apply single factor experiment to study the law that the wear rate and friction coefficient of Al2O3@RGO core-shell ceramic tool materials are affected by variables.The test results show that:with the continuous increase of normal load,the wear rate and friction coefficient of ATC-G@X series and ATB-G@X series tool materials will gradually improve;however,with the continuous increase of sliding speed,both of these parameters show a decreasing trend.Under the same test conditions,the friction coefficients of ATC-G@X series tool materials and ATB-G@X series tool materials increase with the continuous increase of Al2O3@RGO core-shell composite powder content,and then show a continuous first decreasing and then decreasing tends to stabilize.With the continuous increase of Al2O3@RGO core-shell composite powder content,the wear rate shows a trend of first decreasing and then increasing.Compared with the addition of GO,the addition of Al2O3@RGO core-shell composite powder can make the tool material obtain excellent friction and wear properties.There are two main reasons for this:on the one hand,the addition of Al2O3@RGO core-shell composite powder effectively improves the dispersion level of graphene in tool materials.Under the action of sliding speed and normal load,the graphene in the ceramic tool material can be uniformly precipitated,and a complete carbon lubricating film is formed on the friction surface.At the same time,graphene continuously replenishes the carbon lubricating film in a "consumable production" way,which helps to reduce the friction coefficient;on the other hand,the addition of Al2O3@RGO core-shell composite powder improves the interface bonding between the carbon lubricating film and the tool material,so that the carbon lubricating film distributed on the friction surface is closely combined with the tool material.The carbon lubricating film is not easy to fall off or break,and it can also block the direct contact between the friction pairs,so as to play a better lubrication and prevent dispersion wear,and improve the wear resistance of the friction pairs.(5)The effects of different cutting parameters(cutting speed,back engagement and feed rate)on the maximum cutting distance,flank wear and surface roughness of the workpiece of Al2O3@RGO core-shell ceramic tool were studied by cutting test,and the optimal cutting parameters of Al2O3@RGO core-shell ceramic tool were determined.Under the same test conditions,the maximum cutting distance of ATC-G@X series tools and ATC-G@X series tools in the normal wear stage shows a trend of first increasing and then decreasing with the continuous increase of cutting speed.As the back engagement and the feed rate gradually increase,the cutting distance begins to change continuously.With the gradual increase of cutting speed,the surface roughness of the processed workpiece is gradually reduced,but with the back engagement and feed rate,the surface roughness the processed workpiece will increase.The experimental results show that the addition of Al2O3@RGO core-shell composite powder can make the ceramic tool obtain good cutting performance,but also can reduce the temperature in the cutting process,reduce the friction coefficient and the cutting force,so as to improve the surface quality of workpiece.Compared with the ATC-G3.0 tool with GO added,the ATC-G@3.0 tool with Al2O3@RGO core-shell composite powder showed slight wear on the rake face,and the tip of the tool was slightly chipped.The spalling area and depth of the tool surface were far less than that of the ATC-G3.0 tool.Compared with the ATB-G3.0 tool with GO added,the flank face of the ATB-G@3.0 tool with Al2O3@RGO core-shell composite powder only had very light abrasive wear,without diffusion wear or adhesion wear,and the tool tip had tiny edge chipped.