Using metal powder as raw material, tantalum powder was added into niobium powder in two different forms and then mixed with tungsten powder by powder metallurgy method. Then the forming billet was put into graphite crucible and sintered in vacuum carbon tube reduction furnace. Sinter bar sampling analysis, grinding head, get product.
According to the reaction kinetics, NbC dissociates at 1000~1400℃. The reaction equation is 5NbC= 5Nbc0.8 +C, in which [C] is combined with solid solution [O] to form CO to escape through diffusion. At this time, NbC0.8 dissociates again: 10nbCA0.8 =5Nb2C+3C. When the temperature is between 1650 ℃ and 1700℃, the interaction between NbO and Nb2C is accelerated and metal Nb is obtained. The equation is Nb2C+NbO=3Nb+CO↑[2]. In order to achieve the purpose of deoxidation. Because NbO and Nb form a low solubility eutectic at 1915℃, if the furnace temperature exceeds this temperature before NbO phase disappearance, the material will be partially melted and the porosity will be closed, affecting the removal of C and O. Therefore, when heating up, it should be held at 1850℃ for a certain time. Because the reaction stage is completely [C], [O] diffusion plays a leading role, at this time not only to achieve the effect of oxygen reduction, carbon removal, but also to prevent high temperature carburizing (refers to the crucible carburizing). How to determine the final sintering temperature? The data in Table 3 tells us that the temperature control in 1950±50℃ is conducive to deoxidation and carbon removal.
The addition of elements Ta and W in Nb-Ta-W alloy strip is small, and the density of Ta, W and Nb is different, so segregation is easy to occur during mixing. In what form can they be added to Nb to reduce the uniform distribution of Ta and W affected by density? Alloy bar and the national standard of first-class niobium bar sampling site (50mm away from the end) is very different. The so-called end sampling: that is, the two ends of the sintered bar are within the range of 10mm from the end, so the control method of first-class Nb bar on C and O cannot be used to produce the alloy bar. Therefore, at the sintering temperature, how to prevent carburizing is the key.
