Niobium alloy ingot is usually cast by powder metallurgy and vacuum melting. Powder metallurgy the first use of hydrogenation - dehydrogenation process to produce
niobium powder, and then niobium powder and other alloying elements added powder mixing evenly, isostatic pressing, sintering in the sintering furnace at high temperature to get ingot. Vacuum melting method is generally used to make niobium alloy ingot by vacuum electron beam melting and vacuum consumable furnace melting.
Firstly, the niobium powder is the main raw material of
niobium ingot by powder metallurgy. Niobium powder is sintered in vacuum vertical furnace to form the initial electrode of niobium ingot by isostatic pressing
niobium strip. Because of the high melting point of niobium, higher energy is needed in melting, usually not directly use vacuum arc furnace to melt niobium ingot, generally use electron beam melting furnace, through high speed electron beam to melt niobium alloy material. Generally, in order to obtain high purity niobium alloy ingot, niobium strip and alloy element material will be welded into electrode, and two or more electron beam melting to improve the purity of niobium alloy ingot. After vacuum electron beam melting, under high steam pressure, the impurities with melting point lower than niobium, such as aluminum, iron,
titanium, manganese, barium, potassium, silicon and other elements, are easy to evaporate out at the melting temperature of niobium 2470℃, and collected after cooling by the condenser of vacuum electron beam melting furnace. However, low vapor pressure elements such as
tantalum,
tungsten and
molybdenum can hardly be removed in the vacuum electron beam melting furnace, and are usually removed by hydrometallurgy in the previous process. Interstitial elements carbon, nitrogen, hydrogen and oxygen will be released in the form of gas and pumped away by the vacuum furnace; In addition, the oxygen in the niobium alloy can be volatilized in the form of NbO and NbO2, and can also be combined with the carbon of the niobium alloy into CO volatilization. Therefore, the oxygen content in niobium alloy is mainly deoxidized by NbO2, while the carbon element in niobium alloy is mainly removed by excess oxygen. However, when the carbon content is not reduced to the expected effect after a vacuum electron beam melting, vacuum electron beam melting should not be continued. Instead, it would be remelted in vacuum and under higher nutrient conditions, continuing to reduce carbon and possibly increase oxygen in the process.
After purification by electron beam melting, the composition of niobium alloy ingot was analyzed, and the content of alloy elements was adjusted according to the analysis results. The low melting point and volatile alloy elements were added and the vacuum consumable electric arc furnace was melted, so it was easier to get niobium alloy ingot with uniform composition and high purity.
