At present, sponge titanium is one of the main raw materials for the preparation of TC4 titanium alloy. And Kroll method and Hunter method are the two main methods that are generally used to produce sponge titanium. The last factory which uses Hunter method to produce sponge have been closed in 1993. Therefore, Kroll method has become the most common method.

     Kroll method means Magnesium thermal reduction, the reduction principle is TiCl4 vapor can be reduced by liquid or gaseous magnesium, and the total equation is: 1/2TiCl4+Mg=1/2Ti+MgCl2. And the actual reduction process may also go through the stages of TiCl2 and TiCl3, if the amount of magnesium is insufficient, it is difficult to further reduce the low-valent chloride of titanium to metallic titanium, and a secondary reaction of TiCl4 and TiCl4 may occur between titanium and its chloride Therefore, the reduction process must ensure that there is enough magnesium to make the reduction reaction of TiCl4 complete, so as not to produce titanium low-valent chloride. What’s more, the reduction process of reduced magnesium must be carried out under the atmosphere of inert gas protection, the temperature should be controlled below 1248K, and the pressure should rise slowly and periodically. Sponge titanium was then obtained by vacuum distillation after removing magnesium and MgCl2 and cooling. [1]

     After getting the sponge titanium and having put other elements we need into the reacting furnace, VAR method are usually used to smelt titanium alloy. VAR method means vacuum arc melting. The working principle is in the condition of no slag and low pressure or under the protection of inert gas, a consumable level of molten metal at high temperature under low voltage and high current DC arcs, rapidly melting and solidifying into ingots in water-cooled copper crystals. And the metal melting pool is connected to the positive pole and the self-consuming power level is connected to the negative pole, the final alloy casting is obtained by as melting as crystallizing. [2]

     Although Kroll method is widest used now all over the world, it is still a discontinuous process with complex process, long production cycle and high energy consumption. In addition, when TC4 titanium alloy is prepared with sponge titanium, the process flow is long, the production cost is high, and the equipment requirements are also high. The purity of TC4 titanium alloy is low, but the content of impurities is high. Therefore, there is still another way to produce titanium alloy. Although the new method is immature, it still provides us with new ideas. The new method is first mixing vanadium pentoxide, titanium dioxide, aluminum powder and quicklime evenly to get the mixture, and then use aluminothermic reduction reaction to produce coarse TC4 titanium alloy. Finally, preheating the coarse TC4 titanium alloy, and then do the refining to get the pure TC4 titanium alloy. The preparation method is simple, the raw material is cheap, the production cost is low, and is suitable for industrial production, worthy our further thinking and research. [3]