Research On The SPS Preparation Process And Cutting Performance Of Silicon Nitride-based Ceramic Tools

Ceramic cutting tools are highly applied in high speed cutting filed because of their outstanding properties such as high wear resistance,creep resistance and thermal shock resistance.However,the disadvantages of traditional sintering methods such as high energy consumption and low efficiency greatly limit the production of ceramic cutting tools.In this paper,high performance silicon nitride-based ceramic tools were prepared by spark plasma sintering technology?SPS?through optimizing material composition and sintering process.The effects of sintering temperature and additive content on the density,mechanical properties,phase composition and microstructure of silicon nitride-based ceramic tool materials were studied respectively.Then the friction and wear characteristics and wear mechanism under different friction conditions were investigated.Finally,the cutting experiments of the prepared silicon nitride-based ceramic tools were carried out,and the cutting performance and wear mechanism of the tools under different cutting conditions were studied.The influences of sintering temperature and sintering aids?MgSiN₂?Y₂O₃ and CeO₂?on the density,???phase transformation rate,mechanical properties,phase composition and microstructure of silicon nitride ceramic tool materials were studied by orthogonal design experiment?L₉?3⁴??.The results showed that the silicon nitride ceramic tool materials?SN91?with 5wt%MgSiN₂+3wt%Y₂O₃+1wt%CeO₂ had the best comprehensive mechanical properties at 1650?.It had the maximum relative density of 99.40±0.14%,the Vickers hardness of 16.53±0.12GPa,the fracture toughness of 6.89±0.20MPa·m^1/2 and the flexural strength of 1161±134MPa.The grain shapes were composed of equiaxed?-Si₃N₄ and long columnar?-Si₃N₄,and the transformation rate of?-Si₃N₄??-Si₃N₄ was 42.5%.The mechanical properties of SN91 ceramic tool materials sintered by spark plasma sintering were less dispersed,and the hardness and fracture toughness can obey the two parameters Weibull distribution well.Based on the addition of sintering aids,the effects of WC and Co content on the density,phase composition,???phase transformation rate,mechanical properties and microstructure of silicon nitride-based ceramic tool materials at different sintering temperatures were investigated.X-ray diffraction analysis results showed that the sintered samples were mainly composed of?-Si₃N₄,?-Si₃N₄ and WC,and no other obvious sintering additives and new material phases were found.At the sintering temperature of 1650?,the silicon nitride-based ceramic tool materials?SW10?with 10wt%WC+1wt%Co had the optimum comprehensive mechanical properties with the density of 99.04±0.16%,the Vickers hardness of16.96±0.24GPa,the fracture toughness of 7.26±0.17MPa·m^1/2,the flexural strength of1132±201MPa,and the phase transformation rate of 46.21%.Compared with SN91 ceramic tool material,the Vickers hardness,fracture toughness and phase transformation rate of SW10ceramic tool material increased by 2.60%,5.37%and 8.73%respectively.The friction and wear properties of SN91 and SW10 ceramic tool materials were investigated by sliding wear against Si₃N₄?purchased from market?and bearing steel GCr15respectively under dry sliding conditions,and compared with commercially available hot-pressed ST ceramics.The results showed that the friction coefficient and wear rate of Si₃N₄/Si₃N₄ sliding pairs decreased with the increase of sliding speed,and the trend of friction and wear of the three materials were inconsistent in other cases.The paired materials had significant influence on the friction and wear properties of silicon nitride-based ceramic tool materials.The wear rate of Si₃N₄/Si₃N₄ sliding pairs was higher than that of Si₃N₄/GCr15,and the wear rate of ST ceramics was lower than that of the other two kinds of Si₃N₄-based ceramic tool materials.The wear mechanism of different silicon nitride-based ceramic tool materials was different.The cutting performance of silicon nitride-based ceramic tools?SN91 and SW10?for continuous dry cutting of hardened alloy steel 40Cr under different cutting conditions was studied by orthogonal design experiment?L₉?3³??.The results were compared with those of Sialon ceramic tools and cemented carbide tools YG8.Under the same cutting conditions,the cutting life of SN91 tool was the longest among the four kinds of cutting tools,and it showed superior cutting characteristics when machining hardened alloy steel 40Cr.Under the cutting conditions of v_c=103.62m/min,a_p=0.1mm and f=0.05mm/r,the tool life of SN91 was about1.43 times of that of SW10 tool.At v_c=103.62m/min,the wear mechanism of SN91 tool was mainly adhesive wear,accompanied by oxidation wear and diffusion wear;At 214.31 and314.00m/min,the wear of SN91 ceramic tool flank was mainly abrasive wear,accompanied by adhesive and oxidation wear,while the front of tool mainly produced abrasive wear.