This article proposes a niobium-hafnium-titanium-zirconium-tantalum-tungsten alloy and its optimized preparation process. The fabrication procedure adopts a powder metallurgy combined with multi-stage melting and forging strategy. Specifically, tungsten (W), tantalum (Ta), and niobium (Nb) powders are sequentially blended, compacted, and vacuum-sintered to prepare a pre-alloyed blank. The blank is further refined via no fewer than two electron beam furnace melting cycles to obtain a homogeneous Nb-Ta-W master alloy. After surface anti-oxidation coating treatment, the Nb-Ta-W master alloy undergoes hot forging to form a qualified alloy billet. Subsequently, hafnium (Hf), titanium (Ti), and zirconium (Zr) plates are welded to the outer surface of the billet via tungsten inert gas (TIG) welding to fabricate a consumable electrode. Finally, the electrode is remelted at least three times through vacuum consumable melting. This optimized process achieves uniform chemical composition distribution of the multi-component niobium-based alloy, simplifies the overall preparation workflow, realizes precise low-oxygen content control and accurate composition regulation, and effectively eliminates adverse effects on the alloy’s comprehensive performance.
The niobium-hafnium-titanium-zirconium-tantalum-tungsten alloy, commercially known as C-103 niobium alloy, is a typical low-strength and high-ductility niobium-based structural material. It exhibits excellent hot working performance, including superior hot extrusion, hot forging, rolling and weldability, and can be processed into various profiles such as bars, tubes and strips. Benefiting from its outstanding high-frequency vibration resistance and low-temperature tolerance, the alloy is widely applied in aerospace and propulsion systems. Its typical service components include liquid rocket engine nozzle extensions, orbital maneuvering engines, high-ductility attitude control engines, and radiation-cooled thrust chambers, serving as core structural parts for spacecraft, launch vehicles and jet propulsion engines.
Vacuum consumable remelting is the mainstream preparation technology for C-103 niobium alloy, which relies on custom-fabricated consumable electrodes. The core technical difficulty of C-103 alloy preparation lies in the significant melting point difference among constituent elements. As typical refractory metals, W, Ta and Nb have extremely high melting points, which are over 800 ℃ higher than those of Ti and Zr. The alloy takes Nb as the dominant matrix element with high mass fraction, making it impossible to directly compact high-melting-point and high-density W, Ta and Nb together with Hf, Ti and Zr to form integrated consumable electrodes. Accordingly, the rational incorporation method of W, Ta and Nb elements has become the key bottleneck restricting the high-quality preparation of C-103 niobium alloy. The specific melting points of each constituent element are as follows: 3410±20 ℃ for tungsten, 2995 ℃ for tantalum, 2468 ℃ for niobium, 2227 ℃ for hafnium, 1852 ℃ for zirconium, and 1668 ℃ for titanium.
Compared with pure Nb and Ta, conventional Nb-Ta master alloys feature lower melting points and densities, following the melting point gradient: pure Nb, pure Ta, pure W > Nb-Ta master alloy > Ti, Zr, Hf. This characteristic enables relatively stable melting matching between the master alloy and low-melting-point constituent elements during consumable smelting, so the Nb-Ta master alloy doping method has been widely adopted in existing processes for Ta and Nb incorporation. Nevertheless, the Nb-Ta master alloy still possesses higher melting point and density than Ti and Zr during metallurgical preparation. This mismatch easily leads to the generation of unmelted Nb and Ta fragments in the smelting process, inducing microstructural segregation and compositional inhomogeneity in final alloy products. In addition, the secondary addition of alloy scraps may introduce oxygen impurities, resulting in poor low-oxygen content control and unstable alloy performance.
In view of the above defects of existing niobium-based alloy preparation technologies, including prominent microstructural segregation, compositional inhomogeneity, uncontrollable low-oxygen content and inaccurate component regulation that degrade alloy service performance, this work develops a novel niobium-hafnium-titanium-zirconium-tantalum-tungsten alloy and its optimized preparation process. The proposed technology effectively solves the aforementioned technical pain points, realizing uniform chemical composition distribution, simplified preparation procedure, precise low-oxygen control and accurate composition tuning, thereby avoiding performance deterioration of the target alloy.
The optimized preparation process of the multi-component niobium alloy is detailed as follows. First, high-melting-point W, Ta and Nb powders are adopted as raw materials, which are sequentially mixed, electrode-compacted and vacuum-sintered. The obtained pre-sintered blank is subjected to two rounds of electron beam furnace melting to produce a uniform Nb-Ta-W alloy ingot. The ingot is then forged into square alloy bars, and TIG welding is applied to bond Hf, Ti and Zr plates on the bar surface to prepare composite consumable electrodes. After three cycles of vacuum consumable electrode remelting, the homogeneous niobium-hafnium-titanium-zirconium-tantalum-tungsten alloy is successfully fabricated.
In terms of oxygen control, the Nb-Ta-W master alloy is coated with an anti-oxidation layer before hot forging, and the oxide scale generated during forging is completely removed by planing treatment. This procedure greatly inhibits oxygen introduction in the hot working stage and significantly improves the low-oxygen level control accuracy of the final alloy. In terms of composition stability, the adoption of Nb-Ta-W master alloy instead of the traditional Ti-Nb-Ta master alloy eliminates composition deviation and performance degradation caused by the high-temperature volatilization of Ti elements during sintering.
Furthermore, electron beam melting enables sufficient alloying of high-melting-point W and Ta with the Nb matrix, which indirectly reduces the overall melting point of the master alloy. The subsequent vacuum arc remelting realizes effective compounding between the Nb-Ta-W master alloy and low-melting-point Hf, Ti and Zr. During arc remelting, the Nb and Ta phases evolve into a porous scaffold structure, which accelerates the uniform melting and diffusion of high-melting-point metal components. This structural evolution fundamentally eliminates the segregation risk of W, Ta and Nb phases, solves the long-standing problems of microstructural heterogeneity and component segregation in traditional C-103 niobium alloy, and ultimately prepares high-performance niobium-hafnium-titanium-zirconium-tantalum-tungsten alloy with uniform microstructure and stable composition.
