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Research on the Application of NbTi Superconducting Leads in Cryogenic Power Transmission Systems: Resistance to Moist Hydrogen Corrosion Compared to TA2, Ti6Al4V, Pure Niobium, C103, and Molybdenum
Cryogenic superconducting power transmission pipelines and superconducting equipment for hydrogen energy applications operate at an ultra-low temperature of 4.2K for extended periods, simultaneously exposed to trace amounts of moist hydrogen and cryogenic inert carrier gases, facing the risk of hydrogen embrittlement induced by hydrogen atom permeation. Superconducting leads not only need stable superconducting conductivity but must also resist cryogenic hydrogen-induced cracking. The NbTi niobium-titanium alloy solid solution structure exhibits low sensitivity to hydrogen embrittlement, making it a key candidate material for cryogenic hydrogen-coupled superconducting systems. Currently, numerous research institutions are continuously conducting corrosion and hydrogen permeation tests on NbTi in cryogenic hydrogen-containing atmospheres, comparing its hydrogen resistance with that of rare metals such as TA2 pure titanium, Ti6Al4V, pure niobium, C103, and molybdenum, providing material selection criteria for novel hydrogen-superconducting integrated equipment.
Conventional conductive metals cannot meet the dual requirements of cryogenic moist hydrogen and superconductivity. Ordinary carbon steel and nickel-based alloys exhibit extremely high hydrogen embrittlement sensitivity, with crack propagation accelerating dramatically at low temperatures. Copper and aluminum conductors lack superconducting properties, resulting in significant losses during high-current transmission. While titanium alloys TA2 and Ti6Al4V possess excellent corrosion resistance, they still undergo hydrogen-induced embrittlement under high-pressure, low-temperature hydrogen environments and lack superconductivity. Traditional materials struggle to simultaneously achieve lossless superconducting power transmission and resistance to hydrogen corrosion, limiting the development of hydrogen superconducting energy storage equipment.
This text includes numerous horizontal comparisons with the low-temperature hydrogen-containing operating conditions of TA2, Ti6Al4V, pure niobium, C103 niobium alloys, and metallic molybdenum. TA2 and Ti6Al4V exhibit excellent corrosion resistance in acidic and alkaline environments at room temperature, but hydrogen atoms readily form hydrides in the titanium matrix, leading to brittle fracture and making them unsuitable for long-term low-temperature, high-pressure hydrogen environments. Pure niobium can dissolve a certain amount of hydrogen, but excessive hydrogen absorption results in rapid deterioration of mechanical properties. C103 niobium alloys contain hafnium, and hydrogen atoms easily accumulate at the alloy phase interface, inducing localized microcracks. Molybdenum reacts with hydrogen over a long period to form unstable hydrides, causing continuous surface pulverization. NbTi solid solution has a uniform structure, with titanium and niobium atoms mutually inhibiting hydride precipitation, resulting in a hydrogen permeation rate far lower than the aforementioned rare metals, while maintaining stable superconducting properties.
Comparing the internal structure of the niobium-titanium superconducting system, commercially available Nb-47Ti exhibits superior overall hydrogen resistance compared to niobium-titanium alloys with titanium or niobium-based compositions. Excessive titanium content makes the formation of titanium hydrides more likely; while increasing the niobium content inhibits hydride formation, it leads to a decrease in the superconducting critical current. A uniform composite passivation film forms on the surface of standard-ratio NbTi wires, preventing hydrogen atoms from continuously diffusing into the substrate. Combined with a copper stabilizing layer, this further prevents direct contact between the superconducting core wire and wet hydrogen, significantly extending the lead wire's lifespan. Simultaneously, NbTi's good plasticity facilitates the fabrication of irregularly shaped superconducting leads, adapting to complex pipeline sealing structures.
Currently, NbTi superconducting leads have completed long-term integrated testing in a laboratory hydrogen superconducting energy storage prototype. Compared to titanium alloy leads, the risk of hydrogen embrittlement failure is significantly reduced, and low-temperature power transmission stability is greatly improved. However, material limitations also exist. Under conditions of extremely high concentrations of wet hydrogen and temperatures exceeding 500K, the passivation layer still faces the risk of slow penetration. Future research will focus on the development of surface hydrogen-barrier coatings and the refined control of alloy composition. With the simultaneous development of the hydrogen energy industry and superconducting power transmission technology, NbTi, as a rare metal material possessing both superconductivity and resistance to low-temperature hydrogen corrosion, will see its application scenarios continue to expand.
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