SPS Preparation Process And Cutting Performance Of Silicon Nitride-based Special-shaped Ceramic Tools

Silicon nitride ceramic tools have gained attention in the field of high-speed cutting due to their excellent mechanical and chemical properties.However,at present,silicon nitride ceramic tools still have some disadvantages,such as the performance is still not high enough,and the complex surface structure of the tool cannot be prepared,which limit the wider application of silicon nitride ceramic tools.In this paper,based on spark plasma sintering technology,high-performance silicon nitride ceramic tool materials were prepared,and the effect of two-step sintering method on tool materials was studied.The preparation process of special-shaped turning tools was studied under SPS technology,and the experiment of cutting nickel-based superalloys with special-shaped silicon nitride-based ceramic tools was carried out.Si3N4/Ti(C,N)ceramic tool materials having added Ti(C,N),were investigated in this work.The effects of Ti(C,N)addition as well as sintering temperatures on the mechanical properties,phase transformation,and microstructures of Si3N4/Ti(C,N)ceramic tool materials were considered.Ti(C,N)addition promoted the densification and phase transformation,especially at low sintering temperatures.The optimum mechanical properties could be obtained at 1650°C on addition of 10 wt%Ti(C,N).Its relative density,Vickers hardness,and fracture toughness were found to be 99.76±0.07%,17.11±0.38GPa and 7.35±0.64 MPa·m^1/2,respectively.The microstructure of Si3N4/Ti(C,N)was uniform and no abnormal grain growth could be observed.The increase in fracture toughness was attributed to the combination of pulling-out of?-Si₃N₄,crack-bridging,and crack-deflection.The optimum sintering process of two-step sintering is the first sintering temperature is1750?,the second sintering temperature is 1400?,and the holding time is 4min.The sample with a quality equivalent to that of one-step sintering at 1650°C was obtained at a holding temperature of 1400°C.The grain size was reduced by 19.48%from 3.49 to 2.81.The second stage sintering temperature has a significant effect on the two-step sintering.The second stage sintering temperature increased 200?,the aspect ratio increased by 32%while the grain size increased by 76%.Increasing the holding time makes the grain size more uniform,but the grain size increased by 27%.Advant Edge finite element simulation software was used to study the turning of nickel-based superalloys with special-shaped silicon nitride-based ceramic tools.The preparation process of special-shaped ceramic tools was researched.The optimal tool angle is5°rake angle,0.8mm corner radius.The back engagement is the most important factor that affects the cutting force,and the cutting speed is the most important factor that affects the cutting temperature.The best preparation process parameters for special-shaped silicon nitride based ceramic tools are sintering temperature 1650?,sintering pressure 70MPa,holding time 6min,graphite amount 0.5g,respectively.The surface morphology is intact,no doping and consolidation of graphite powder and silicon nitride powder has occurred.Orthogonal experiment(L9(3³))was carried out for determining the best parameters for cutting nickel-based superalloys with special-shaped tools,the cutting parameters were cutting speed vc=75m/min,back engagement ap=1.0mm and feed rate ap=1.0mm.The maximum tool life of the special-shaped tool with 10wt%Ti(C,N)added is 280s.The special-shaped tool has a chip breaking function,and the chips are annular spiral chips.Compared with the flat silicon nitride ceramic turning tool of the same material,the life of the special-shaped turning tool is3.5 times that of the flat turning tool,which proves that the special-shaped process can effectively improve the life of the silicon nitride ceramic tool.Compared with commercial tool,the tool life of SNT20 was five times that of commercial tool under high cutting parameters.Even if the cutting speed was reduced by 1/3,the material removal of SNT20special-shaped turning tool was still 42.8%more than that of commercial tool.