The preparation method of NbTiTa alloy casting ingot for superconducting includes: mixing niobium powder and tantalum powder according to the weight ratio of 4 to 1, isostatic pressing after mixing, vacuum sintering to obtain NbTa sintered bar, and the bar is melted twice by vacuum electron beam to obtain Nb25Ta casting ingot; The ingot is heated to 300 degrees Celsius and kept warm for more than two hours to forge Nb25Ta bar; The raw material of NbTiTa alloy is determined according to the measured composition of the bar. The raw material of the alloy includes: Nb25Ta bar, titanium sponge, TiTa powder or TiNb powder; Titanium sponge is coated with TiTa powder or TiNb powder and pressed to form titanium electrode block. Several titanium electrode blocks and bars were assembled and welded to form a rod-like consumable electrode, and the consumable electrode was melted by vacuum consumable arc three times to obtain NbTiTa alloy ingots.
In NbTiTa alloy, the melting point of tantalum element is as high as 3017℃, the density is as high as 16.60g/cm3, the melting point of niobium element is as high as 2469℃, the density is as high as 8.57g/cm3, while the melting point of active metal titanium is only 1668℃, the density is only 4.50g/cm3, and the melting point and density of the three elements are very different. It is very easy to produce Ta and Nb non-frit in vacuum consumable arc melting, and the preparation technology of ingot is very difficult. When preparing titanium alloys containing refractory elements, the usual way is to first prepare the intermediate alloy by powder metallurgy or melting, and then prepare titanium alloys containing refractory elements. However, it is difficult to control the impurity elements, the purity of the material is poor, and the finished product is high. On the one hand, because the melting point of Ta element is much higher than that of Ti element, the risk of tantalum not frit in the intermediate alloy is greater. On the other hand, due to the high content of Ta and Nb in the alloy, when the proportion of intermediate alloy chips is too large, it is easy to fall off in the smelting process, and the metallurgical risk is large.
The invention realizes the preliminary alloying and pure purification of Nb and Ta by combining the method of powder metallurgy and vacuum electron beam melting, and obtains Nb25Ta cast ingot with lower melting point and lower content of impurity elements; 2. Because of the high vacuum and high power of vacuum electron beam furnace, it is difficult to accurately control the composition of Nb25Ta bar. According to the measured composition of Nb25Ta rod, a small amount of TiTa mixed powder or TiNb mixed powder is added, which not only ensures the precise control of composition, but also ensures the low content of impurity elements. The mixed powder is distributed in the middle of titanium sponge to prevent Nb and Ta non-frit caused by powder leakage; 3. By rationally arranging the relative positions of NbTa rod, mixed powder and titanium sponge, pressing the shaped titanium electrode block, short-circuit heating to increase the temperature of NbTa rod during primary melting, reasonable design of primary melting process, solving the problem of Ta and Nb non-melting, and realizing the pure purification of alloy, precision of composition and preliminary alloying.
