| In the dry cutting,the friction between the tool and the workpiece was decreased by using self-lubricating ceramic cutting tools,and then the reduction of cutting force and cutting temperature was realized.However,self-lubricating ceramic cutting tools often reduced the mechanical properties of the cutting tools while realizing self-lubrication of the cutting tools,which affected the further application of self-lubricating ceramic tools.In view of this technical problem,this paper proposed a technical scheme of adding nano-particles modified by surface coating as solid lubricant,and with whiskers for synergistic toughening ceramic cutting tools.Nano-Ca F2 precursor was prepared by precipitation method,and nano-Ca F2particles with good dispersibility and uniform particle size were obtained by azeotropic distillation,the average particle size of 30-50nm.Ca F2@Si O2 coated nanoparticles with core-shell structure were prepared by coating Si O2 on the surface of nano-Ca F2particles with non-uniform nucleation method and sol-gel method.The effects of process parameters on the microstructure and surface morphology of nano-coated particles were studied,and the optimal preparation process parameters of Ca F2@Si O2coated nanoparticles were obtained:TEOS dosage of 3m L,p H value of 8.5,drop acceleration of TEOS of 0.4m L/min,reaction temperature of 40°C,azeotropic distillation treatment.The coating thickness of Ca F2@Si O2 coated nanoparticles can be controlled between 1.5 and 15 nm.The Al2O3/Ti C/Si Cw/Ca F2@Si O2 self-lubricating ceramic tool materials were prepared by adding Ca F2@Si O2 coated nanoparticles and Si C whiskers simultaneously.The experimental results showed that the bending strength,fracture toughness,hardness of the ceramic cutting tool materials with 10vol.%Ca F2 and 20vol.%Si C whiskers were 598MPa,5.23MPa·m1/2,15.43GPa respectively.The ceramic cutting tool materials with 10vol.%Ca F2@Si O2 coated nanoparticles and 20vol.%Si C whiskers had the best comprehensive mechanical properties,and its bending strength was 712MPa,the fracture toughness was 6.89 MPa·m1/2,and the hardness was16.52GPa.Compared with Al2O3/Ti C/Si Cw/Ca F2 ceramic tool materials,the above properties are improved by 31.74%,19.06%and 7.06%respectively.The reason was that the addition of Si C whisker can achieve better toughening effect,but reduced the compactness of the material.The Ca F2@Si O2 coated nanoparticles not only enhanced the interfacial bonding strength between whiskers and matrix,but also made up for the decrease of compactness caused by adding Si C whiskers.The addition of Ca F2@Si O2coated nanoparticles can refine the crystal grains and induce transgranular fracture,further enhance the mechanical properties of ceramic materials.The cutting performance of Al2O3/Ti C/Si Cw/Ca F2@Si O2 ceramic cutting tool with10vol.%Ca F2@Si O2 coated nanoparticles and 20vol.%Si C whiskers for cutting 40Cr quenched and tempered steel was studied.The cutting experiments showed that under the same cutting conditions,compared with Al2O3/Ti C/Si Cw ceramic cutting tool,the Al2O3/Ti C/Si Cw/Ca F2@Si O2 ceramic cutting tool had lower surface roughness of workpieces,while the main cutting force and cutting temperature are reduced by46.2%and 31.7%respectively in the cutting process.The reason was that Ca F2in the coated nanoparticles was precipitated during cutting process,forming a uniform and continuous lubricating film on the surface of the ceramic cutting tool.The rake face wear of the ATS ceramic tool was mainly adhesive wear,while the flank wear was mainly abrasive wear,and there were also micro-chipping edges.The main wear forms of the rake face of the ATSC@10 ceramic tool were bond wear,and the main wear forms of the rake face wree bond wear and abrasive wear.With the addition of coated nanoparticles and whiskers,ceramic tools have good lubricity while maintaining high cutting performance. |
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