A casting method for manufacturing superconducting NbTi alloy involves purifying and casting high-melting-point niobium metal into ingots to form niobium rods; pressing lower-melting-point, sponge-like active metal titanium into semi-cylindrical tiles; welding the niobium rods and tiles into consumable electrodes under inert gas protection; and then subjecting the electrodes to secondary or higher arc melting. The NbTi alloy obtained using this invention is free of inclusions, exhibits high uniformity, few interstitial elements, and good plasticity, making it extremely advantageous for manufacturing fine-core, high-current-carrying-capacity, and low-cost alloy materials for large-scale applications.
Methods for preparing NbTi superconducting alloys include using niobium powder and titanium fines as raw materials to prepare consumable electrodes, assembling electrodes using niobium plates and titanium plates, and welding niobium rods and titanium rods together. Electrodes prepared using these different methods, when melted and cast in a vacuum arc furnace more than twice, often contain macroscopic inclusions such as incompletely melted niobium and titanium spots, resulting in inhomogeneity and a high concentration of interstitial element impurities in the NbTi superconducting alloy ingot. This affects the cold working plasticity of the superconducting material and severely impacts its superconducting current-carrying capacity. Furthermore, the electrode preparation process for melt-cast NbTi superconducting alloy ingots, both domestically and internationally, involves complex and time-consuming processes for processing raw materials such as niobium and titanium, resulting in significant external contamination and an increase in interstitial elements, thus reducing the superconducting alloy's plasticity. This is extremely detrimental to the manufacture of fine-core, high-current-carrying-capacity NbTi alloy superconducting materials.
A method for manufacturing a superconducting NbTi alloy involves purifying and casting a high-melting-point niobium ingot to form a niobium rod; pressing a lower-melting-point, sponge-like active metal, titanium, into semi-cylindrical tiles; welding the niobium rod and tiles together under inert gas protection to form a consumable electrode; and then performing at least two arc castings.
The preparation process of the niobium rod is as follows: First, the purified niobium ingot is machined into a niobium rod meeting dimensional requirements, and then machined to remove the surface contamination layer, with a removal amount of at least 1 mm.
The first arc casting is carried out in a vacuum consumable arc furnace with a melting power of 200kW-500kW, forming a deep and wide molten pool in the water-cooled copper crucible. High-superheated component melts are dripped into the molten pool, and the highly fluid melt is violently stirred in the pool by electromagnetic force and high-temperature, strong heat flow, casting into a primary superconducting alloy ingot.
At least two more arc castings are performed, with the previous alloy ingot undergoing high-power casting at a power of 300kW-600kW. The method of this invention involves welding semi-circular cylindrical tiles, formed by pressing high-melting-point metal ingots with lower-melting-point sponge active metal, to prepare consumable electrodes. Both components melt into a molten mass during consumable melting, and under strong electromagnetic stirring, the molten components are thoroughly mixed, effectively promoting alloy homogenization and avoiding unmelted lumps in the ingot. This method is simple, produces minimal external contamination, has high production efficiency, and is low in cost. The resulting NbTi alloy is free of inclusions, highly uniform, has few interstitial elements, and good plasticity, making it extremely advantageous for manufacturing fine-core, high-current-carrying-capacity, and low-cost alloy materials for large-scale applications.
Purified niobium ingots are forged into rods and machined to remove the surface contamination layer (at least 1 mm). Using niobium rods with a diameter of Ф86×1450mm, sponge titanium is pressed into 8 semi-circular cylindrical tiles as shown in Figure 1. Each tile weighs 7.72 kg. The niobium rods and tiles are then welded together under argon protection, ensuring a strong and smooth weld. The electrode was first melted in a vacuum arc remelting furnace at a power of 250 kW. The resulting niobium-titanium superconducting alloy ingot was then used to form a niobium-titanium consumable electrode with a diameter of 220 mm. This electrode was then remelted in the same furnace at a power exceeding 300 kW, with thorough stirring to further homogenize the niobium and titanium, resulting in a secondary niobium-titanium alloy ingot.
Purified niobium ingots were forged into rods and machined to remove a surface contamination layer of at least 1 mm. Using 80×1450 mm niobium rods, sponge titanium was pressed into eight semi-cylindrical tiles as shown in Figure 1. Each tile weighed 9.2 kg. The niobium rods and tiles were then welded together under argon protection, ensuring a strong and smooth weld. The electrode was first melted in a vacuum arc furnace with a melting power of 230kW. The niobium-titanium superconducting alloy ingot obtained after the first melting was made into a niobium-titanium arc furnace with a diameter of 220mm. The ingot was then remelted in a vacuum arc furnace with a melting power of over 300kW. The melt was thoroughly stirred to further homogenize the niobium and titanium, resulting in a secondary ingot of niobium-titanium alloy.
