Research On Preparation Process And Properties Of TiB₂-based Toughened And Reinforced Ceramic Cutters

Ceramic cutting tools,with excellent cutting performance of high hardness,toughness and wear resistance in dry cutting conditions,are suitable for the cutting of difficult-to-machine material as Ni based single crystal alloys,alloy structural steel,hardened steel and so on,and have good prospects for application.The titanium diboride matrix composite ceramic tool materials had some problems such as unclear material system,difficult preparation,high hardness but low flexural strength and fracture toughness,poor cutting performance.This paper based on the project“National Natural Science Foundation?51405326?”,aims to develop the materials with high performance according to design principles of composite ceramic tool materials.The vacuum hot-pressing technology is applied by using three types of new Titanium diboride matrix composite ceramic tool materials such as TiB₂-20 wt.%HfC?TH20NC3??TiB₂-20wt.%HfC-32 wt.%TiC?TH20C32NC?and Ti B₂-20 wt.%HfC-24wt%TiN?TH20N24NC?,are fabricated by adding metal phases and reinforced phases.The reinforced phases are HfC?TiC and TiN,The metal phases are Ni?Co??Ni,Co?and?Ni,Mo?.The mechanical properties,the microstructure,toughening mechanisms,friction and wear mechanisms,the cutting performance and failure mechanisms of tools were fully studied.The main contents of the research are as follows:1)Research on the preparation process and technology of cutting tools.The influence on the microstructure and mechanical properties of the new TiB₂-based ceramic cutting tool materials are studied about material composition and sintering parameters.The material component and sintering parameters based on the mechanical properties index are optimized with fuzzy vector single value method,then three types of Ti B₂-based ceramic tool preparation,TH20NC3 TH20C32NC and TH20N24NC,are confirmed with high flexural strength,high toughness and hardness.Hardness and toughness of cutter tool are properly matched.2)The influence of microstructure on mechanical properties of tool materials.The microstructure and fracture morphology of the cutting tool materials under different preparing conditions were studied.The toughening-reinforcing model and crack growth model are established,which are based on the synergy of the core-shell structure and HfC dispersive particle.The coupling structure of the core-shell structure and particle dispersion under the synergistic effect are revealed to make the toughening and reinforcing mechanism of the ceramic tool material.The results show that the core-shell structure and the dispersion of HfC particles exist in the TiB₂-HfC and TiB₂-HfC-TiN ceramic tool materials,in which the core consists of TiB₂ grains and the"shell"consists of the complex solid solution formed by the matrix phase,the enhanced phase and the metal phase.TH20NC3 and TH20C32NC toughening reinforcing mechanism of cutting tool is the"core-shell structure and HfC particle dispersion;TH20N24NC toughened and reinforced mechanism of cutting tool is HfC particle dispersion;The fracture mode of three types of ceramic cutting tool is the inter granular fracture and trans granular fracture.3)The research on friction and wear properties.Three typical hard materials including316 austenitic stainless steel,TA2 titanium alloy and YG6X hard alloy were studied.The results showed that the friction coefficient and the rate of wear of the three tool materials with three typical hard-machining materials have the similar varying tendency under the same experimental conditions,that is the friction coefficient decreased with an increase of load and sliding velocity,and the rate of wear increased with an increase of load and sliding speed;TH20NC3 tool material has a good wear resistance with austenitic stainless steel 316 and hard alloy YG6X.TH20C32NC tool material has a good wear resistance with titanium alloy TA2.The main wear mechanisms of the three tool materials with austenitic stainless steel 316,titanium and hard alloy YG6X are adhesion abrasion and oxidative corrosive wear,and adhesion abrasion with titanium alloy TA2,and abrasive particle abrasion with hard alloy YG6X respectively.4)Study on cutting performance.The author designs orthogonal experiment based on speed decreasing method under dry and with coolant conditions,and studies the tools cutting performance and fail forms under continuously cutting conditions with three types of hard machined materials,and obtains the optimum cutting parameters.The results show that under the condition of wet cutting,TH20NC3 tool cuts continually the 316 austenitic stainless steel at a cutting speed of 180 m/min,a feed rate of 0.1 mm/r,a cutting depth of 0.15 mm,it shows good cutting performance,the surface roughness can reach 0.4?m;Under the condition of dry cutting,TH20NC3 tool cuts the Cr12MoV hardened die steel at a cutting speed of 60m/min,a feed rate of 0.1 mm/r,a cutting depth of 0.15mm,it shows good cutting performance,the surface roughness can reach 0.95?m;Under the condition of dry cutting,TH20NC3 tool cuts 38CrMoAlA alloy structural steel at a cutting speed of 110 m/min,a feed rate of 0.1 mm/r,a cutting depth of 0.1mm,it shows good cutting performance,the surface roughness can reach 0.27?m.In addition,under the same cutting conditions,by comparing the cutting performances of the three types of tools developed with commercial cutting tools,TH20NC3 tool shows good cutting performance under dry cutting conditions.The results of the research show that based on fuzzy analytical method of fuzzy vector decrement of speed and orthogonal experiment,the coupling structure of the core-shell and coexist-structure of Hfc particle can be realized in the vacuum hot pressing sintering process.The TiB₂ based toughening and reinforcing ceramic tool with high flexural strength,high toughness and hardness can be achieved.It can solve the problems of difficult preparation,bending strength and low fracture toughness of TiB₂ based ceramic tools.It provides a basis for the production and application for new cutters.