Study On The Preparation, Structure And Property Of Ultra-fine Binderless WC Cemented Carbide

In this paper, pure WC powder with a average diameter of0.2μ m was used as rawmaterial to prepare Ultra-fine binderless WC cemented carbide with a serious of processing,namely, ball milling, pre-forming, pre-sintering and high temperature sintering followed byhot pressing. The phase composition of the WC powder and cemented carbide was analyzedby X-ray diffraction determination; the effects of ball milling on WC particle size werestudied by laser particle size analyzer; the density and the density of the compacts of greenand WC carbide were measured by electronic balance; the microstructure of WC cementedcarbide morphology was observed by scanning electron microscopy and optical microscopy;the hardness and bending strength of the alloy were tested by Vickers hardness tester anduniversal testing machine. The effects of the milling time, pre-pressure and sinteringtemperature on the microstructure and properties of WC cemented carbide were discussed,and the optimal processing parameters of ultra-fine binderless WC cemented carbide weredetermined.The experiment results show that WC particle size gradually decreases with theincreasing milling time. When the milling time is12hours, the particle size is about d(50)=194nm, and the particle size does not change significantly when the milling time is extendedto18h. The green density increases gradually with the enlarging molding pressure. The greencompacts exhibit a good appearance without cracks and off side when the pressure is increasedto500Mpa.The highest density of9.62g/cm~3of green compact is obtained in with theparameters of12h milling, compacting at500MP. The green compact are sintered at and hotpressed at890MPa for10s to prepare WC carbide. The density and hardness WC cementedcarbide are increased with the increasing sintering temperature. The densities of alloyssintered at1150,1230and1300℃are11.6g/cm~3,15.2g/cm~3,and15.6g/cm~3, and theharnesses are1736HV,2259HV,2320HV respectively.The bending strength of alloy sintered at1300℃is739MPa, slightly lower than that ofthe alloy sintered at1230℃,864MPa. This phenomenon should be attributed to theabnormal grain growth at1300℃. The fracture surface exhibits a loose combination betweenWC powders in the specimens sintered at1150℃, but features of cleavage fracture can befound on the fracture surface of alloys sintered at1230℃and1300℃, besides, sphericalpores between the powder and grain are observed. High sintering temperatures are believed to contribute to the improvement of atomic diffusion, and thust can reduce the porosity andimprove the interfacial bonding strength.The optimal processing parameters of ultra-fine binderless WC cemented carbide are asfollows: the milling time is12h, pre-pressure of500MPa, pre-sintering at200℃for1h,450℃for1h,550℃for30min, and800℃for30min for dewaxing, sintering at1230℃andmaintaining pressure at890MPa for10s. The WC carbide prepared by this technologypossess the best performance with a density of15.2g/cm3, hardness of2259HV, and bendstrength of864MPa.