Study On SPS Sintering Of Hafnium Carbide And Tungsten Carbide

Refractory metals are a kind of rare metals,which easily form carbides with stable chemical properties with carbon,and have the advantages of high melting point and high hardness.In order to explore the sintering mechanism of refractory metal carbides and meet the needs of industrial production,the paper adopts the spark plasma sintering（SPS）method,and selects HfC with the highest melting point and the most widely used WC as the experimental material to prepare high density,High-performance HfC,explored the general law of the preparation of refractory metal carbides by SPS,further prepared high-density and high-performance WC and WC-6Co,and explored the best process for solid-phase connection.The SPS technology was used to sinter nano-level pure HfC powder,and the effects of sintering pressure and sintering temperature on the density of HfC microstructure and mechanical properties were studied.The results show that when the axial pressure is 50MPa and the sintering temperature is 1900℃,the density and hardness of HfC both reach the maximum,which are 95.4%and 1793HV,respectively.In order to further improve the performance of HfC,2.5wt.%ultrafine carbon powder was added to pure HfC powder by mechanical powder mixing,and the best sintering process of pure HfC was used to sinter the mixed powder.The results showed that the density of the sintered body was increased to 96.1%,and the Vickers hardness was reduced to 1721HV.X-ray diffractometer（XRD）showed that the sintered block had no impurity phases,and scanning electron microscope（SEM）observed that there were no large defects on the whole surface,and there were a few holes locally.Using the method of SPS technology and ball milling powder,the sintering process of ultra-fine crystal pure WC powder with a particle size of 0.4μm was studied.The results show that the best sintering temperature of pure WC is 1800℃,the best holding time is 0～5min,and the axial pressure is 40MPa.Under this process,the density,Vickers hardness,and fracture toughness of WC are 99.1%,2410HV,and13.54MPa·m^1/2,respectively.In order to improve the performance of WC,the inhibitor VC with different mass fractions was added by means of ball milling and powder mixing.The results show that the density of WC is maintained in the range of 98%to99%,the mechanical properties are improved,and the Vickers hardness is increased by16.5%to 2807HV.The SPS technology was used to explore the best compaction process for ultra-coarse WC-6Co powder.The results show that the best sintering parameters are sintering temperature 1200℃,axial pressure 40MPa,holding time for5minutes,density can reach 98.7%,Vickers hardness is 18.9%lower than pure WC to1954.4HV,fracture toughness is increased by 31.5%to 17.8MPa·m^1/2.SPS technology was used to connect the prepared WC and WC-6Co by solid-phase diffusion.The results show that the best connection parameters are the connection temperature of 1200°C,the axial pressure of 40MPa,and the holding time of 30min.The shear strength of the connector under the best process reaches 315.1MPa.The mechanical properties of the base member before and after the connection are compared and tested.The hardness of WC near the joint decreases and the fracture toughness increases.The hardness of WC-6Co remains basically unchanged,and the fracture toughness decreases.Combined with the SEM results,it shows that the bonding phase Co has diffused,and the rest of the base has no performance changes.