Study On Preparation Process And Mechanism Of Ultrafine/Nanocrystalline WC-Co Cemented Carbide

Ultrafine/nanocrystalline WC-Co cemented carbides have"double high"properties（high hardness and high strength）,and are widely used in integrated circuit boards,precision molds and other fields of cutting materials,is an important research branch in the field of cemented carbides.The preparation of nano powders,grain growth inhibitors and sintering technology are the main research directions of ultrafine/nanocrystalline cemented carbides.In this paper,using the lab-made ultrafine/nanocrystalline WC powder and commercial Co powder as the main raw materials,adding appropriate amount of VC and Cr₃C₂ as grain growth inhibitors,using vacuum sintering and hot pressing sintering technology to prepare ultrafine/nanocrystalline WC-9.5Co cemented carbide,The effects of different sintering temperatures on the phase,microstructure and mechanical properties of ultrafine/nanocrystalline WC-Co cemented carbides were studied by TG-DSC thermal analysis,XRD,SEM,hardness and fracture toughness analysis.The effects of vacuum sintering and hot pressing sintering on the microstructure and mechanical properties of the ultrafine/nanocrystalline WC-Co cemented carbides prepared with nano-WC powder as raw material were compared and analyzed.At the same time,the influence of hot pressing sintering,using nano-WC powder and ultrafine WC powder as raw materials on the microstructure and mechanical properties of ultrafine/nanocrystalline WC-Co cemented carbides were compared and analyzed.The research conclusions are as follows:（1）Ultrafine/nanocrystalline cemented carbide is prepared by vacuum sintering and hot pressing sintering with nano-WC powder as raw material at different sintering temperatures.The results show that the mechanical properties of the samples are closely related to relative density and average grain size.With the increase of sintering temperature,the porosity of the alloy decreases,the relative density increases,the WC grain is coarsened,the hardness and fracture toughness of the sample will also increase with the increase of relative density.The hardness decreases with the increase of the average particle size of the alloy,and the fracture toughness increases with the increase of the average particle size of the alloy.The hardness of the alloy increases first and then decreases,while the fracture toughness increases gradually.（2）When nano-WC powder is used as raw material,the optimum sintering temperature for vacuum sintering is 1380℃,and the microstructure of the alloy is relatively uniform.The average grain size is 214 nm,the relative density is 98.5%,the hardness is 2100 HV_0.5,and the fracture toughness is 11.0 MPa·m^1/2.The results show that the optimal sintering temperature is 1360℃,the average grain size is 196 nm,the relative density is 99.5%,the hardness is 2312 HV_0.5,and the fracture toughness is 13.0MPa·m^1/2.Under the optimum sintering conditions,the hot pressing sintering temperature is 20℃lower than the vacuum sintering temperature,and the comprehensive properties of the alloy prepared by hot pressing sintering are better than those prepared by vacuum sintering.（3）When the sintering temperature is 1360℃,the properties of cemented carbide prepared with nano-WC powder are better than those prepared with ultrafine WC powder.The results show that the WC grains of WC-Co sintered body prepared by ultrafine WC powder are coarse,there are obvious abnormal growth grains in the alloy,and the microstructure uniformity is poor.The average grain size is 482 nm,the relative density is 99.2%,the hardness is 1697 HV_0.5,and the fracture toughness is 11.2MPa·m^1/2.