| The machinability of nickel-based superalloy is mainly characterized by serious tool wear.Aiming to the tool wear characteristics in high speed machining nickel-based superalloy,the relationship between tool failure life and properties of tool materials have been established,which aims to improve wear resistance of tools.Mechanical properties prediction models of ceramic tool materials have been established.A novel ceramic tool with good cutting performance has been developed,which can be well used for dry and high speed machining nickel-based superalloy GH4169.The relationship between the fracture life,wear life and properties of ceramic tool materials was established.The property design objectives of ceramic tool materials used for high speed maching nickel-based superalloy were proposed.It was found that the tool fracture life was more significantly affected by the flexural strength than the fracture toughness.The flank wear life of ceramic tool was much more affected by hardness than fracture toughness.The influence of the fracture toughness on the notch wear life was greater than that of hardness.And the wear resistance of ceramic tool could be improved by the refined grains and the residual compressive stress at grain boundary.The prediction models of fracture toughness,hardness and the optimal content of nanoparticle for ceramic tool material were established,and the thermal shock resistance was also analyzed.The composition and content of ceramic tool materials were then designed.The fracture toughness of ceramic tool material reinforced by whisker was predicted,through which the SiC whisker content was determined to be 20 vol%.Based on the residual thermal stress and the percolation cluster theory,the calculation equation in optimal content of nanoparticle was established.Then,the optimal content of TiC nanoparticle was determined to be 4 vol%.The hardness prediction model of composite ceramic tool material was set up.The error between the experimental hardness and the theoretical hardness was-0.15?+3.21%.The ceramic tool material components were designed to be 76 vol%of Al2O3 matrix,20 vol%of SiC whisker and 4 vol%of TiC nanoparticle.The preparation process of ceramic tool materials was studied.A novel type of composite ceramic tool material was developed.The toughening mechanism of ceramic tool materials reinforced by nanoparticle and whisker was revealed.The mixing process of composite powders including nanoparticle and whisker was developed.The well-dispersed composite ceramic powders were obtained in the process that the organic solvents were mostly removed under ultrasonic vibration environment before vacuum drying.The conventional hot pressing sintering process was improved by replacing the soft graphite paper used in the conventional hot-pressing process with artificial graphite powder which was conducive to the gas discharge.The relative density of ceramic tool material can be improved by the new sintering process.The prediction equation for the optimal content of nanoparticle was verified.The optimum sintering process of ceramic tool material was obtained,sintering at 1700 ? under 30MPa for 30 min.The mechanical properties of the ceramic tool material under optimal sintering process were obtained,such as hardness of 21.18 GPa,fracture toughness of 6.04 MPa·m1/2 and flexural strength of 744.05 MPa.The toughening mechanism of ceramic tool materials reinforced by nanoparticle and whisker was studied.Nanoparticle can cause transgranular fracture and crack deflection,and further to improve the fracture toughness of tool materials.The change law of hardness,fracture toughness and flexural strength of Al2O3-20 vol%SiCw-4 vol%TiCn(ASWT)and Al2O3-20 vol%SiCw(ASW)ceramic tool materials were studied at high temperature.The evolution of the microstructure of the composite ceramic material at high temperature was also studied and its influence on the mechanical properties was then analyzed.It was found that the high temperature hardness and fracture toughness of composite ceramic materials were improved by TiC nanoparticle,which was able to enhance the wear resistance of ceramic tool materials.TiC nanoparticle increased the flexural strength at room temperature,but reduced the high temperature flexural strength of ceramic tool materials.The hardness of the two kinds of ceramic tool materials decreased linearly with an increase in temperature(from 20 to 1000 ?).The fracture toughness decreased firstly and then increased to a peak at 1200 ? with an increase of temperature.The change mechanisms of high temperature mechanical properties of ceramic tool materials were studied.The high temperature hardness of nano-ceramic tool materials was improved due to the intragranular structure.Liquid phase produced by SiC whisker oxidation,hindering crack propagation,and the plastic deformation of the material at 1200 ? were the main factor in improving the fracture toughness.The grains of the material were refined by TiC nanoparticle,forming a higher grain boundary ratio.The flexural strength of ceramic tool material was reduced by the weakening and sliding of the grain boundary at high temperature.The cutting performance and friction characteristics of ASWT novel ceramic tool in high speed machining nickel-based superalloy were studied.The cutting tool edge type and cutting parameter range were formulated.The friction characteristics between ASWT ceramic tool material and nickel-based superalloy GH4169 were studied by using the ceramic pin-superalloy ring friction pair.The cutting speed domain was simulated and determined to be 250?400 m/min through friction test.The simulation of ASWT ceramic tool in high speed machining GH4169 was studied.Based on the temperature and stress distribution on ceramic cutting tool,the cutting edge was determined to be round type.The cutting parameters of ASWT ceramic tool for dry and high speed machining GH4169 were drawn,ie cutting speed 250?400 m/min,feed rate<0.08 mm/r.The cutting performance of ASWT ceramic tool in dry and high speed maching nickel-based superalloy was studied.The results showed that the affecting order of cutting parameters on material removal was cutting speed,feed rate and depth of cut.The cutting parameters in dry and high speed cutting GH4169 for ASWT ceramic tool were a cutting speed of 400 m/min,a feed rate of 0.04 mm/r and a cutting depth less than 3.0 mm.The material removal was 192000 mm3 and the tool life was 240 s which was 50%higher than that of commercial ceramic tool CC670.The failure modes of ceramic cutting tool included tool flank wear and notch wear.Tool fracture was inhibited by crack healing which was caused by the molten oxidation of ceramic tool materials.The cutting performance of ASWT novel ceramic tool in wet and high speed machining superalloy GH4169 was studied.The results showed that the optimized cutting parameters in wet and high speed cutting GH4169 for ASWT ceramic tool were a cutting speed of 400 m/min,a feed rate of 0.06 mm/r and a cutting depth of 2.5 mm.The main failure modes of ceramic cutting tool were notch wear,fracture on rake face and flank wear.The tool failure was dominated by the notch wear.The adhesive wear was reduced because of the transgranular fracture and the pull-out effect caused by nanoparticle and SiC whisker,respectively. |
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