Study on Al2O3-Ti(C,N)-(W,Ti)C New Composite Ceramic Tools

Author:Yu Jin Wei

Supervisor:huang chuan zhen

Database:Doctor

Degree Year:2019

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Pages:170

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Hard-to-process materials are being constantly emerged,it is urgent to develop high-performance cutting tool materials which can solve practical problems in production.In this paper,Al2O3-based composite ceramic tool materials with high performance have been developed by adding Ti(C,N)and(W,Ti)C to Al2O3 matrix.The composition and sintering process of Al2O3-based composite ceramic tool material were designed.The effect of microstructures of ceramic tool materials on mechanical properties of ceramic tool materials was studied.The toughening mechanism,high temperature flexural strength,cutting performance and tool wear reliability of tool materials were studied.Al2O3-Ti(C,N)-(W,Ti)C composite ceramic tool material system was designed.The sintering process of Al2O3-Ti(C,N)-(W,Ti)C composite ceramic tool was studied.The effect of sintering process on the mechanical properties and microstructures of Al2O3-Ti(C,N)-(W,Ti)C composite ceramic tools at room temperature was studied.The better room temperature mechanical properties of composite ceramic tool AT20W20 were obtained when sintering temperature was 1700℃,holding time was 20 minutes,sintering pressure was 32 MPa and heating rate was 50℃/min.Its Vickers hardness was 20.21 GPa,fracture toughness was 6.57 MPa·m1/2 and flexural strength was 901 MPa.The better room temperature mechanical properties of composite ceramic tool AT20W25 were obtained when sintering temperature was 1650℃,holding time was 20 minutes,sintering pressure was 32 MPa and heating rate was 50℃/min.Its Vickers hardness was 19.39 GPa,fracture toughness was 6.36 MPa·m1/2 and flexural strength was 941 MPa.The strengthening and toughening mechanisms of Al2O3-Ti(C,N)-(W,Ti)C composite ceramic tool material was studied.The results show that the main toughening mechanisms are grain refinement,fracture mode change,crack coalition and branch,crack deflection,micro-crack toughening,residual stress toughening,nano-particle toughening and reinforcing effect.The variation of high temperature flexural strength of Al2O3-Ti(C,N)-(W,Ti)C composite ceramic tool with temperature was studied.The stochastic distribution function model of high temperature bending strength of tool and its reliability model were established.The flexural strength of AT20W20 and AT20W25 decreases rapidly as the temperature is raised from 20℃ to 1100 ℃.At 1100℃,the flexural strength of AT20W20 is higher than that of AT20W25.The fracture toughness of AT20W20 and AT20W25 decreases with an increase in term of temperature between 20℃ and 1100 ℃.The fracture toughness of the two ceramic tool materials decreases slowly between 700℃ and 850 C,and still maintains high fracture toughness at 850 C.The decrease of fracture toughness of AT20W20 is slower than that of AT20W25,and the fracture toughness of AT20W20 is higher than that of AT20W25 at the same temperature.The probability of flexural strength of ceramic tool AT20W20 and ceramic tool AT20W25 obeys Weibull distribution at the high temperature.When the reliability is 90%,the flexural strength of AT20W20 and AT20W25 ceramic tool material is 720.9 MPa and 658.7 MPa respectively at 800 C.The cutting performance of alumina-based composite ceramic tools was studied,and the stochastic distribution function model and reliability model of cutting tool life of Al2O3-Ti(C,N)-(W,Ti)C composite ceramic cutting tool are established.The cutting performance and reliability of alumina-based composite ceramic cutting tools AT20W20 and AT20W25 for wet cutting stainless steel(1Cr18Ni9Ti)are studied,the experimental results show that the optimal cutting parameters obtained by AT20W20 ceramic cutting tools are v=120m/min,ap=0.1mm,f=0.15mm/r,and the material removal ratio is 1609mm3/min,and the tool wear life is 17 minutes.The tool life obeys lognormal distribution.When the reliability level of tool is 80%~90%,the reliable tool life of AT20W20 ceramic tool is about 9~10 minutes.The optimum cutting parameters of AT20W25 ceramic tool are v=120m/min,ap=0.1mm,f=0.15mm/r.And in this case,the material removal ratio is 1591mm3/min and the tool wear life is 14 minutes.When wet cutting austenitic stainless steel 1Crl8Ni9Ti,the failure forms of AT20W20 and AT20W25 cutting tools are brittle fracture at the cutting edge,micro-avalanche and material spalling in local area of flank face.The wear mechanisms are abrasive wear and adhesive wear.The cutting performance and reliability of alumina-based composite ceramic tool AT20W20 developed in the present research for wet cutting die steel(Cr12MoV)were studied.The results show that the optimal cutting parameters obtained by AT20W20 ceramic tool are v=80m/min,ap=0.1mm,f=0.1mm/r.In this case,the material removal ratio is 795.55mm3/min and the tool wear life is 15 minutes.The tool life distribution obeys logarithmic normal distribution.When the tool reliability level is 80%~90%,the reliable tool life of AT20W20 ceramic tool is about 7.5~8.3 minutes.The breakage forms of AT20W20 tool are brittle fracture at the cutting edge,micro-breakage of cutting edge and material spalling in local area of flank face.The main wear mechanism is abrasive wear and adhesive wear.