The mainstream production process for niobium-tantalum-tungsten alloy strips is powder metallurgy. It is mainly used as raw material for high-temperature alloys such as C103. The key to this technology lies in ensuring the uniformity of the alloy composition and controlling the content of gas impurities (such as carbon and oxygen).
Raw materials and blending (ensuring uniform composition): The process starts with high-purity niobium powder, tantalum powder, and tungsten powder. The first technical challenge is how to mix metal powders with different densities and properties evenly. Therefore, in addition to the conventional direct mixing method, sometimes a more advanced pre-alloying process is adopted, that is, first make Nb-Ta intermediate alloy powder, and then mix it with tungsten powder. This can more effectively prevent component segregation. Raw material selection (high-purity powder): Nb powder (≥99.95%), Ta powder, W powder, and in some formulas, Zr powder (Nb-Ta-W-Zr);
Particle size: Nb: 3-8 μm, Ta: 4-10 μm, W: 2-5 μm; strictly control O < 150 ppm, C < 80 ppm (sampling at the end for detection requirements). Weigh precisely according to the formula (e.g., 80% Nb - 10% Ta - 10% W).
Compression and sintering (to control impurity content) uniformly mixed powder is made into a certain strength billet strip through metal die pressing or cold isostatic pressing (CIP). The most crucial step is high-temperature sintering, which is usually carried out in a crucible sintering furnace or a vacuum sintering furnace. The core task of this stage is: controlling the carbon and oxygen content: the product has very strict requirements for carbon, oxygen and other gas impurities. Research shows that controlling the O/C ratio in the raw materials and adopting an appropriate final sintering temperature are the key process parameters to ensure that the impurity content of the product meets the standards. Efficient powder mixing (core anti-component segregation) V-type three-dimensional mixing machine, vacuum sealed mixing for 20-28 hours; inert argon protection to avoid oxygen absorption; passing through a 120-mesh sieve to disperse agglomerated particles and ensure that Ta/W is uniformly dispersed in the Nb matrix. Cold pressing molding (formed into square billet strips) equipment: 300-500t vertical hydraulic press; common specifications of cross-section 25×25/30×30mm, length 300-600mm; green billet strips; pressing pressure 180-230MPa, green billet density 62%-68% theoretical density, no layering or cracks.
To prevent carbon diffusion during the sintering process, additional measures need to be taken to prevent carbon from seeping into the product from the equipment or the environment, thereby ensuring the purity of the alloy. The alloy strips obtained from the subsequent processing (from billet to material) through sintering will be further processed into shapes such as rods, plates, and wires according to the requirements of the final product. For alloys with a high tungsten content (such as Ta10W), the processing difficulty will significantly increase, and often special heat treatment or processing techniques are required, such as applying an anti-oxidation coating on the surface and then conducting graded heating forging to improve their processing ductility. Vacuum high-temperature sintering (vacuum carbon tube furnace / molybdenum wire furnace) with staged temperature rise (total vacuum ≤ 5×10⁻³ Pa): room temperature → 600℃: hold for 2 hours, remove adsorbed oxygen and water vapor; 600 → 1300℃: hold for 3 hours, reduce impurity C/O; 1300 → 1950~2100℃, hold for 4~6 hours for solid-phase diffusion alloying; after sintering, the density of the billet strip is 92%~95%, completing Nb-Ta-W solid solution alloying.
