SiC_w Whisker And MoSi₂ Synergistically Toughened Si₃N₄ Matrix Ceramic Tool And Cutting Performance

Because of its high hardness,high wear resistance,high temperature resistance,abundant resources and low price,Si₃N₄ceramics have become one of the common matrix materials for ceramic tools.In order to solve the brittleness of Si₃N₄ceramic tool and further expand its application scope,effective reinforcement has been a research hotspot.At present,the toughening of Si₃N₄ceramic tools is mainly to add a single toughening phase or a metal phase,but the single toughening method is difficult to significantly improve the toughness of Si₃N₄ceramic tool materials.The addition of metal phase makes it difficult to effectively balance the toughness and high temperature stability of Si₃N₄ceramic tool materials.In order to ensure the excellent comprehensive performance of ceramic tool materials,intermetallic compounds Mo Si₂and SiC_wwhiskers were added to Si₃N₄.The new composite ceramic tool material Si₃N₄/Mo Si₂/SiC_wwith good comprehensive mechanical properties was prepared under the optimized sintering process by exerting the synergistic toughening and reinforcing effect of whiskers and intermetallic compounds.The physical and chemical compatibility of the matrix phase and the additive phase was analyzed,and each phase had good chemical compatibility and physical compatibility.A new type of composite ceramic tool material Si₃N₄/Mo Si₂/SiC_w（SMC）with good comprehensive mechanical properties was prepared under the optimized sintering process.Mechanical properties of SMC composite ceramic tool materials were tested and microstructure was observed.The results showed that the fracture toughness of SMC gradually increased with the increase of SiC_wcontent.With the increase of Mo Si₂content,the flexural strength of SMC gradually increased.The fracture toughness and bending strength of SMC3（Mo Si₂10wt.%,SiC_w10wt.%）with SiC_wand Mo Si₂were880.21 MPa and 10.22 MPa·m^1/2,respectively.Its fracture toughness is 49.8%higher than that of SMC1（Mo Si₂10wt.%,SiC_w0wt.%）with Mo Si₂only.Its bending strength was 27.7%higher than that of SMC5（Mo Si₂0wt.%,SiC_w10wt.%）with SiC_wonly.The bridge and pull-out of SiC_weffectively improved the fracture toughness of Si₃N₄,and the fracture mode gradually changed from intergranular fracture to transgranular fracture and intergranular fracture.At the same time,the intermetallic compound Mo Si₂effectively filled the gap between the matrix and the reinforcement.The pores were significantly reduced,and the grains were refined to a certain extent,which significantly improved the bending strength of Si₃N₄.The friction and wear properties of SMC composite ceramics were tested and the wear morphology was observed.The effects of the addition amount of binder phase and reinforcement phase on the friction,wear and cutting performance were studied.The results show that when SMC ceramic tool material is used to grind GCr15bearing steel ball,with the increase of SiC_wcontent,the friction coefficient of SMC increases gradually,the weight loss and wear depth of SMC decrease significantly,and the wear form gradually changes from adhesive-abrasive composite wear to abrasive wear.With the increase of Mo Si₂content,the friction coefficient of SMC gradually decreased,the weight loss and wear depth of SMC gradually increased,and the wear form gradually changed from abrasive wear to adhesive wear.The cutting performance of SMC composite ceramic tool was tested and the wear morphology of the tool was observed.The effects of single toughening and synergistic toughening tools on the cutting performance were studied.When SMC ceramic tool continuously dry cutting 45#hardened steel,the tool life and cutting reliability of SMC composite ceramic tool are improved significantly compared with commercial tool YBC251.The tool life of SMC3 and SMC5 with SiC_wis better than that of SMC1without SiC_w.With the increase of cutting depth,SMC5 without Mo Si₂is prone to chipping,and the cutting reliability is not as good as SMC3 with synergistic toughening.