Fabrication And Performance Of Microwave Sintering New Titanium Carbonitride Based Cermet Cutting Tool

Titanium nitride-based cermet have become an indispensable tool material in the field of industrial production.However,the fabrication of Ti(C,N)-based cermet tool materials by traditional sintering method had some problems such as long holding time and coarse grains.Microwave sintering technology based on material self-heating principle has been used for the fabrication of high-temperature structural ceramic in recent years,with the advantages of short holding time.In this thesis,for the characteristics of large size and high power of the purchased microwave sintering equipment,a new type of Ti(C,N)-based cermet tool material was fabricated by refining the structure of the microwave sintering heat preservation device and analyzing the influence of the green compact height for internal electric field distribution.The material composition,sintering process parameters,microwave sintering densification process and tool cutting performance were researched.According to the characteristics of microwave sintering and the physical and chemical compatibility principle of composite ceramic tool materials,a new tool material system Ti(C0.7,N0.3)-WC-HfN-Ni-Mo was proposed to improve the microwave absorption property and sinterability and the mechanical properties of tool materials in this thesis.The COMSOL Multiphysics simulation software was used to analyze the electric field distribution of the green compact at different heights of the microwave sintering furnace chamber.It was found that when the green compact was placed at a height of 320mm,the internal electric field intensity was relatively high and evenly distributed.The effects of Ni-Mo content on the microstructure and mechanical properties of new Ti(C,N)-based cermet tool materials by microwave sintering were firstly studied.The results showed that when 5wt.%Ni and 5wt.%Mo were added,the microstructure of the tool materials was uniform,the relative density was high,and the mechanical properties were better.On this basis of the tool material system Ti(C,N)-15wt.%WC-5wt.%Ni-5wt.%Mo(TWNM10),the addition of HfN in the new Ti(C,N)-based cermet tool material by microwave sintering was optimized.The results showed that when the HfN content was 20wt.%,the mechanical properties and microstructure of the cermet were better,the bending strength,Vickers hardness,fracture toughness were about 812MPa,16.8GPa,8.1MPa·m1/2,and the relative density was 98.7%.Combined with the microstructure analysis,the toughening mechanism was crack deflection and crack bifurcation caused by the mixed transgranular/intergranular fracture mode.The preparation process parameters such as sintering temperature,holding time and cold pressure of the microwave sintering new material system Ti(C,N)-15wt.%WC-20wt.%HfN5wt.%Ni-5wt.%Mo(TWH20NM)were optimized.The results showed that when the sintering temperature was 1400℃ the holding time was 10min,and the cold pressure was 300 MPa,the comprehensive mechanical properties of TWH20NM were the best,and the Vickers hardness was increased to 17.3GPa.The mechanical properties and microstructure of pressureless sintering TWH20NM cermet when sintered at different temperature were studied and compared with the samples when microwave sintered at 1400℃.The results showed that under the same experimental conditions,microwave sintering can obtain better density and better mechanical properties,better microstructure uniformity and finer grain size.The densification process of microwave sintering was analyzed.The research showed that under the action of microwave electric field,the transfering rate of vacancies on the surface of the grains was accelerated,the grain boundaries slip,and the surfacefree energy decreases.Compared with the traditional pressureless sintering process,the driving force of microwave sintering TWH20NM cermet increased.The microwave electric field promoted the migration of charged vacancies and the densification rate increased.Moreover,under the action of microwave electric field,the grain produced plastic deformation,and the surface free energy was reduced,which promoted the discharge of pores at the trifurcate grain boundary and accelerated the densification.The cutting performance of TWH20NM cermet tool by microwave sintering was investigated when continuously wet turnning hard-to-cutting material Hastelloy C-276.The orthogonal experimental results showed that Cutting speed had the greatest influence on material removal,the second was cutting depth,the least influence factor was feed rate.The optimal machining parameters were v=40m/min、ap=0.2mm、f=0.125 mm/r.Compared turning tests with two commercial ceramic tools SG4 and LT55 under this parameter,the results showed that the order of wear resistance from strong to weak was SG4>TWH20NM>LT55.The main failure modes of TWH20NM cermet tool were groove wear on rake face,micro chipping edge and flank wear.The main wear mechanisms were adhesive wear,diffusion wear and oxidation wear.