Study On The Preparation And Cutting Performance Of Carbon-nanotubes-toughening Si₃N₄-based Ceramic Tools

Ceramic cutting tool has high hardness,wear resistance and resistance to oxidation at high temperature.It is applicable for high speed machining and dry machining.However,the brittleness of ceramic cutting tool limits its application.Toughening and reinforcing is an urgent problem to be solved in the development of ceramic cutting tool.In this paper,Si₃N₄-based ceramic cutting tool was developed by vacuum hot pressing sintering with micro-Ti C and Carbon nanotubes（CNTs）as reinforcing phase.The effects of CNTs contents on the microstructure and mechanical properties of Si₃N₄-based ceramics cutting tool materials were investigated.The cutting performance of the Si₃N₄-based ceramics cutting tool was investigated,too.The Purification and dispersion process of carbon-nanotubes were investigated.The optimal dispersion: the CNTs were put in the dilute solution of concentrated nitric acid,ultrasonic dispersion time is 30 min and the setting time is 24h;ultrasonic dispersion time is 3h and the setting time is 24h;ultrasonic dispersion time is 3h and the setting time is 2h.The vaccum filtration was used by vacuum suction machine.The distilled water was used to clean the CNTs until PH is 7.At last,The CNTs were put in the vacuum drying box.The dispersion technology of CNTs was studied.The optimal dispersion parameters: the mass ratio of dispersant and carbon nanotubes were 1:1,ultrasonic dispersion time was 30 min.The effects of CNTs addition on the microstructure and mechanical properties of Si₃N₄-based ceramics cutting tool material were studied.Experiments results showed that when CNTs content was 1wt%,the Si₃N₄-based ceramics cutting tool material had the optimal mechanical properties.The hardness is 14.5GPa,flexural strength is 850 MPa,fracture toughness is 8.8MPa·m1/2.Compared with the Si₃N₄-based ceramics cutting tool material which did not have CNTs,the hardness,flexural strength and fracture toughness were increased by 9.8%,21% and 10%.Using the new Si₃N₄-based ceramics cutting tool cutting gray cast iron continuously was studied.The cutting tool had better wear resistance properties at high cutting speed,lower feed rate and less cutting depth,the main wear mechanism are adhesion wear and abrasive wear.The process of research on wear mechanism showed that the flank face was smoother when CNTs was added.This is because that the CNTs fill and repaire the friction surface.The surface roughness ranges from 2μm to 5μm.At the same cutting parameters,the cutting temperature of SCT tool is lower than ST tool,the cutting force of SCT tool is smaller than ST tool.Generally speaking,the Si₃N₄-based ceramics cutting tool which was designed and prepared can effectively improve the cutting performance.