Study On Preparation And Oxidation Resistance Of Binderless WC-based Cemented Carbide

The binderless WC-based cemented carbide has good wear resistance,oxidation resistance and good polishability,thus making it an important application in the field of precision molds.However,there are many problems in the preparation process of the binderless WC-based cemented carbide:for example,the binderless WC-based cemented carbide is very sensitive to the requirements of carbon content,and decarburization will occur during the sintering process;There is no bonding phase,which makes it difficult to densify the WC-based cemented carbide without bonding phase.At present,the sintering of binderless WC-based cemented carbide mostly adopts methods such as discharge plasma,hot isostatic pressing and vacuum hot pressing,but they all have the problems of expensive equipment and high cost.Therefore,this subject uses a vacuum pressureless sintering preparation process.By introducing TaC into it,the solid solution reaction of TaC and WC is used to promote densification,and at the same time,TaC is used to improve the high-temperature oxidation resistance.The main research contents and conclusions of this paper are as follows:1.In this study,the vacuum-free pressureless sintering method was used to prepare binderless WC-based cemented carbide samples with different carbon contents.The carbon contents were 0.1%,0.2%,0.3%and 0.4%,respectively.?X-ray diffraction,XRD?was used to characterize the sintered alloy sample.when the carbon content was 0.2%,the main phase of the sample was WC,and there was no carbon-deficient phase.Scanning electron microscope?Scanning electron microscope,SEM?was used to characterize the sample.when the carbon content was greater than 0.2%,the grains on the surface of the alloy sample showed abnormal growth.When the carbon content is 0.2%,the surface pores are the least.The metallographic structure and physical and mechanical properties of the samples were analyzed.The results showed that the carbon content increased from 0.1% to 0.4%,according to the metallographic determination of GB/T3489-2015 cemented carbide porosity and non-combined carbon,the porosity of the samples is A08B08C00,A04B06C00,A06B06C00,A08B08C00;Vickers hardness is 1795.7 HV₃₀,1971.0 HV₃₀,1902.4HV₃₀,1765.7 HV₃₀;Density is 14.46 g/cm³,14.68 g/cm³,14.50 g/cm³,14.29g/cm³,respectively.Because of the excessive carbon addition,the physical and mechanical properties of the alloy samples will be reduced.Therefore,it can be concluded that when the carbon content is 0.2%,the physical and mechanical properties of the alloy samples are the best.2.Based on the determined 0.2% carbon content,the sintering densification mechanism of the binderless WC-based cemented carbide with different TaC content and its effect on the physical and mechanical properties of the alloy were studied.The TaC content was 0%,2.5%,5%,7.5% and 10%,respectively.XRD was used to characterize the sintered alloy samples.The results showed that the lattice constant a and c of WC both increased,and the lattice constant a increased from 0.290963 nm to 0.291838 nm.The lattice constant c increased from 0.284075 nm to 0.284929 nm.The samples were characterized by SEM.when the TaC content is 2.5%,the grain size of the sample is the smallest,the minimum value is 0.41?m.When the TaC content is greater than 2.5%,WC grains all grow abnormally to varying degrees,and the average grain size increases from 0.41?m to 0.54?m.The metallographic structure and physical and mechanical properties of the sample were analyzed.The results showed that when the TaC content increased from 0%to 10%,according to the metallographic determination of GB/T3489-2015 cemented carbide porosity and non-combined carbon The porosity is A04B06C00,A02B02C00,A06B06C00,A04B04C00,A08B08C00;Vickers hardness values are 2132.8 HV₃₀,2376.4 HV₃₀,2043.3 HV₃₀,2068.3 HV₃₀,1992.4 HV₃₀;Fracture toughness are 6.56 MPa·m^1/2,7.08MPa·m^1/2,5.72 MPa·m^1/2,5.99 MPa·m^1/2,5.53 MPa·m^1/2,respectively.The density reached 14.92 g/cm³,15.07 g/cm³,14.94 g/cm³,14.97 g/cm³and 14.90 g/cm³,respectively.The hardness of the binderless WC-based cemented carbide sample is mainly determined by its density value.The greater the density,the greater the Vickers hardness value.Therefore,it can be concluded that when the TaC content is 2.5%,the physical and mechanical properties of the alloy samples are the best.The Vickers hardness is 2376.4 HV₃₀,the fracture toughness is 7.08 MPa·m^1/2,and the density is 15.07 g/cm³.3.The densification process of WC-0.2%C-2.5%TaC binderless carbide was studied.XRD was used to characterize the sintered alloy samples.The results showed that the main phase of the alloy samples after sintering at different temperatures was WC.The samples were characterized by SEM.when the sintering temperature was 1700?,the alloy sample was not sintered and dense,and the sintered sample had more holes;when the sintering temperature was 1750?,the alloy sample had holes Gradually decrease;when the sintering temperature is 1800?,the grain size of the alloy sample begins to increase unevenly;when the sintering temperature is 1850?,the alloy sample has the least holes.Compared with the other three sintering temperatures,when the sintering temperature is 1850?,the alloy structure is more dense.By analyzing the metallographic structure and physical and mechanical properties of the sample,the results show that when the sintering temperature is increased from 1700? to 1850?,according to the metallographic determination of GB/T3489-2015 cemented carbide porosity and non-combined carbon,The porosity of the alloy samples is A06B06C00,A04B06C00,A04B04C00,A02B02C00;Vickers hardness is 2091.2 HV₃₀,2119.7 HV₃₀,2200.4 HV₃₀,2376.4 HV₃₀.The density is14.55 g/cm³,14.78 g/cm³,14.94 g/cm³,15.07 g/cm³,respectively.As the sintering temperature continues to increase,the porosity of the alloy samples continues to decrease,and the Vickers hardness and relative density values continue to increase.Therefore,when the sintering temperature is 1850?,the corresponding physical and mechanical properties are also the best.4.The high temperature oxidation behavior of alloy samples with 0.2%C content and 2.5% TaC content was studied.The results show that when the oxidation temperature is increased from 500?to 700?,the oxidation weight gain of the alloy samples increases sequentially;XRD is used to characterize the alloy samples.When the oxidation temperature is 500?,the main phase is still WC;when When the oxidation temperature is 600?,the main phases are Ta₂O₅ and WO₃;when the oxidation temperature is 700?,the main phases are WO₃;it can be seen that as the oxidation temperature increases,the oxidation resistance of the alloy samples decreases in turn;When the oxidation time increases from 1 h to 3 h,the oxidation weight gain of the alloy samples increases in sequence;XRD is used to characterize the alloy samples.When the oxidation time is 1 h,the main phases are Ta₂O₅ and WO₃;when When the oxidation time is 2 h and 3 h,the main phase of the alloy sample is WO₃;the sample is characterized by SEM.The surface of the alloy sample oxidized for 3 h is compared with the surface of the alloy sample oxidized for 2 h.Increased surface porosity.Therefore,with the prolongation of the oxidation time,the oxidation resistance of the alloy samples gradually weakened.