Study On Structure And Properties Of WC-10Co Alloys By Microwave Sintering

Ultra-fine WC-Co cemented carbides with superior hardness and toughness are key materials of machining tools in the modern manufacturing industry.Nowadays, nanostructured WC-Co powder has been successfully synthesized.But because of the abnormal grain growth of nano-powder during the sintering processing,how to control the grain growth of WC has been the key problem of the fabrication of ultrafine hardmetals.The microwave sintering,which has many advantages such as decreased sintering temperature,enhanced heating rate and volumetric heating compared to the conventional sintering,is a newly developed sintering method.Fine grain ceramics with finer and much uniform grain size can be fabricated using microwave sintering technology.In this study,the orthogonal experiment was carried out to optimize the parameters of high energy ball milling for the formation of nanostructured WC-10Co composite firstly.Then we analyze the microwave sintering processing of WC-Co powder.We also study the effects of VC/Cr₃C₂ additions and Co content on the microwave sintering properties of WC-Co alloys,the chemically-activated sintering and the interaction between WC-10Co and microwave electric field,magnetic field,elctromagnetic field.Finally,we summarize the mechanism of microwave processing in inorganic materials.It has been found that milling time is highly significant to refining process,and the ratios of ball to powder and volume of ethanol are also benefit to the refining of WC-10Co composite.But specific mixed ball size in this experiment is not significant to the refining process.The final milling parameters were optimized according to the orthogonal experiment result and SEM micrograph.In the microwave processing of WC-10Co alloys,we found that sintering temperature and dewaxing time are the key factors to affect the properties of the samples.While soaking time and heating rate are just the secondary factors.It can be obtained a kind cermet with fine and uniform grain size and favorable properties after microwave dewaxing at about-610℃for 20min,then microwave heating to 1320℃· for soaking 15min.From the X-ray analysis,we found that the hardmetals have normal structure of WC andγphase.Doped with 0.6wt%VC/Cr₃C₂,WC grain growth could be effectively controlled and the WC-Co cermets accordingly had excellent properties.WC-Co alloys have favorable microwave adaptability,but Co content can have some effects on the sintering temperature and densification of WC-Co alloys.As to the WC-10Co cemented carbides,incorporating of small quantity of P and Ni will form liquid phase at lower temperature,which can accelerate the speed of densification and effectively decrease the sintering temperature.With 0.3wt% addition of phosphorus,near full density cermets could be obtained at 1250℃.For the WC-10Co doped with 0.3wt%P and 0.3wt%Ni,its full density could be realized only at 1200℃.When combined with the presence of inhibitors of VC and Cr₃C₂,the properties of cermets could be improved.But segregation phenomenon may occur in the microstructures of WC-Co when the Ni and P were doped,which would damage the properties of alloys,and so the quantity of Ni and P must not be excessive.In the microwave sintering of WC-10Co cemented carbides,magnetic losses was the main loss mode at lower temperature,while conductive losses and dielectric losses would get the run upon at higher temperature.So we can sinter WC-Co in pure E-field or mixed field.But W₂C would appear when the samples were sintered in mixed field,which was harmful to the properties of cermets.The mechanism of microwave sintering in ceramic materials is analyzed according to thermodynamics.Microwave E-field has orientation effect,which can accelerate the diffusion rate of particles and thus accelerate heating rate of materials. As to the different materials,such as ceramics and metal powder,their microwave sintering mechanisms are also different and have diverse features respectively.