Research Of (Ti,W)C Cermet Tool Based On Ultrafast Sintering And Its Cutting Performance

In recent years,with the development and application of high-speed machining,green and environmentally friendly dry cutting speed is favored by people,which undoubtedly puts forward more stringent requirements on the mechanical properties of the tool itself.In order to prepare high performance cermet tools suitable for high speed dry cutting,（Ti,W）C cermet tools with dense microstructure and excellent mechanical properties were prepared by spark plasma coupled high frequency induction sintering（SPS-HF）technology under ultrafast sintering conditions.The ultrafast sintered cermet tool has the characteristics of continuous gradient distribution of structure and performance,and forms residual compressive stress on the tool surface,thus effectively improving the mechanical properties and cutting performance of the tool.Firstly,（Ti,W）C cermet tool materials were prepared via spark plasma coupled high frequency induction sintering technology,and the effects of ultrafast heating rate on the sintering behavior,microstructure and mechanical properties of cermet tools were studied.The results show that slow sintering prolongs the time of grain growth,leading to the grain coarsening of cermet materials during heat preservation;while the electric field generated by proper rapid sintering enhances the mass transfer of metal liquid phase,restrains the grain size of cermets,and improves the densification process of the material.The optimum sintering rate of（Ti,W）C cermet tool is 500℃/min,and its flexural strength,fracture toughness,Vickers hardness and relative density are 1340.90±23.55MPa,11.96±0.23 MPa·m^1/2,18.42±0.46 GPa and 99.56±0.15%,respectively.Then,the electric-thermal-magnetic-mechanical coupling finite element model was established using the finite element simulation software COMSOL Multiphysics,and the electric current,solid heat transfer,magnetic field and solid mechanical physical field were coupled to study the distribution and variation of electromagnetic field,temperature field and stress field in（Ti,W）C cermet tool material at ultrafast sintering rate.The current density on the surface and interior of cermet materials is different,and the current distribution directly affects the energy generation rate per unit volume during the ultrafast sintering process of SPS-HF,thus affecting the temperature gradient in the sintering process.In addition,the stress distribution depends on the grain growth related to temperature.On the other hand,the continuous gradient distribution of（Ti,W）C cermet tools under ultrafast sintering was analyzed.The results show that due to the“gradient”sintering effect,the grain growth state of tool materials is different,and the grain size of（Ti,W）C ceramic phase decreases gradually from the surface to the interior.At this time,the surface grain is larger,and the metal liquid phase is mainly concentrated at the trigeminal junction of the adjacent grains;the internal grain is smaller,and the metal liquid phase is dispersed uniformly among the grains due to grain refinement.Considering the above factors,the tool surface forms residual compressive stress with high hardness,while the internal interface has excellent bonding strength and good strength and toughness.Finally,using the single factor test method,the high-speed dry cutting experiments of austenitic 304 stainless steel were carried out under different machining parameters,and the effect of ultrafast sintering on the cutting performance of（Ti,W）C cermet tools was investigated.The results show that,compared with conventional sintering,the ultrafast sintering cermet tool reduces the three-way cutting force,shear energy and friction energy in the cutting process due to the existence of residual compressive stress in the surface layer.As a result,the cutting temperature and friction coefficient are significantly decreased,and the surface machining quality of the workpiece is improved.In addition,the continuous gradient distribution of structure and performance formed by ultrafast sintering enhances the wear resistance of the tool,improves its wear resistance,and the service life of the tool is increased by 14.29%.At the same time,the optimal cutting parameters for dry cutting austenitic 304 stainless steel are v_c=300 m/min,a_p=0.10 mm,and f=0.102 mm/r.The rake face of ultrafast sintered（Ti,W）C cermet tool is mainly adhesive wear,accompanied by slight diffusion wear;while the flank face is mainly abrasive wear and adhesive wear.