Nickel and nickel alloy thin-walled tubes for vacuum devices
Nickel and nickel alloy thin-walled tubes for vacuum devices are key materials used in the internal structures of devices such as vacuum electron tubes, microwave tubes, and X-ray tubes. Thanks to their excellent high-temperature resistance, low vapor pressure, and excellent vacuum performance, nickel and nickel alloys maintain structural stability in high-vacuum, high-temperature environments, ensuring the proper functioning of the devices. These thin-walled tubes typically have an outer diameter of 0.5-20mm and a wall thickness of 0.05-1mm. Materials primarily include pure nickel (N4, N6), nickel-copper alloys (Monel 400), and nickel-chromium alloys (Inconel 600). Pure nickel tubes are suitable for general vacuum applications, while alloy tubes are used in high-temperature (500-1000°C) or corrosive environments, such as those used in vacuum devices in the nuclear industry.
The production process for nickel and nickel alloy thin-walled tubes used in vacuum devices requires precision processes including vacuum melting, ingot casting, hot extrusion, cold rolling (or cold drawing), bright annealing, and precision machining. First, electrolytic nickel with a purity of 99.95% or higher, or a suitably formulated alloy, is melted in a vacuum induction furnace at a vacuum of ≤ 1×10⁻³Pa and a temperature of 1450-1550 °C. Electromagnetic stirring is used to homogenize the composition. Pure nickel tubes have a nickel content of ≥ 99.5% , while alloy tubes have an alloying element tolerance of ≤ ± 0.1% . The ingots are then remelted using a vacuum consumable electrode process to produce round ingots with a diameter of 50-100mm . This process reduces gas content (oxygen ≤ 0.005% , hydrogen ≤ 0.0001% ) and non-metallic inclusions to ensure the tubes’ vacuum performance. Hot extrusion heats the ingot to 900-1100°C and extrudes it through a die into a rough tube. The extrusion ratio is controlled at 8-15, ensuring a smooth, scale-free inner tube surface. Cold rolling or cold drawing is the core process for producing thin-walled, high-precision tubes. This process involves multiple passes, each with a diameter reduction of 10%-15% and a wall reduction of 5%-10%. Lubrication is performed using specialized lubricants (such as sulfurized lard) to ensure an outer diameter tolerance of ≤±0.01mm, a wall thickness tolerance of ≤±0.005mm, and an inner wall roughness Ra ≤0.4μm. Bright annealing is performed under vacuum or hydrogen protection. Pure nickel tubes are heated to 700-800°C, while alloy tubes are heated to 900-1000°C. After holding for 1-2 hours, they are slowly cooled to eliminate work hardening, reducing the tube hardness to HV80-120 and achieving an elongation of ≥30%. Finally, precision cutting and end grinding are performed to ensure a perpendicularity of ≤0.01mm at the tube end.
The performance advantages of nickel and nickel alloy thin-walled tubes used in vacuum devices make them irreplaceable in the vacuum field. First, they offer excellent vacuum performance. Nickel and its alloys have extremely low vapor pressures ( pure nickel vapor pressure ≤ 1× 10⁻⁴Pa at 1000 °C ). They release virtually no gas in high vacuum environments, maintaining a vacuum of 1×10⁻⁶Pa or higher inside the device, thus preventing electron beam scattering. Second, they offer excellent high-temperature stability. Pure nickel tubes and Inconel 600 tubes maintain stable mechanical properties below 600°C, with a tensile strength of ≥ 400MPa and excellent oxidation resistance, with an oxidation rate of ≤ 0.1g/(m²・h) . Third, they offer excellent processability. Annealed thin-walled tubes can be bent and welded, with a minimum bending radius of up to three times the tube diameter. Argon arc welding is used for welding, achieving weld strength ≥ 90% of that of the parent metal . Fourth, they offer low magnetism. Pure nickel is paramagnetic at room temperature, with a magnetic permeability of ≤ 1.005μ₀. , to avoid interfering with the magnetic field distribution of electronic devices; fifthly, strong corrosion resistance, Monel 400 and other nickel-copper alloy tubes have excellent resistance to corrosive media such as seawater and acid mist, and are suitable for vacuum devices in harsh environments.
Nickel and nickel alloy thin-walled tubes for vacuum devices are core components of many high-end electronic devices. In microwave communications, the electron guns and collector cooling systems of klystrons and traveling wave tubes utilize pure nickel thin-walled tubes with an outer diameter of 1-5 mm and a wall thickness of 0.1-0.3 mm to ensure vacuum tightness in high-frequency electric fields. In medical equipment, the anode cooling channels of X-ray tubes utilize thin-walled Inconel 600 tubing, designed to withstand temperatures exceeding 800°C and high-pressure coolant. In semiconductor manufacturing, the vacuum chamber connectors of ion implanters utilize Monel 400 tubing to resist plasma corrosion. In the nuclear industry, the vacuum housings of nuclear radiation detectors utilize thick-walled (0.5-1 mm) nickel alloy tubes, providing both shielding and vacuum performance. In aerospace, traveling wave tubes for satellite communications utilize ultra-thin nickel tubes (outer diameter 0.5-1 mm) to reduce device weight and adapt to space environments. With the development of 5G communications and high-end medical equipment, the requirements for the precision and reliability of thin-walled tubes are increasing.
Industry trends indicate that nickel and nickel alloy thin-walled tubes for vacuum devices are trending toward ultra-fine diameters, ultra-thin walls, and multifunctional applications. Breakthroughs in production technology for ultra-fine, thin-walled tubes have enabled the stable production of pure nickel tubes with an outer diameter of 0.3mm and a wall thickness of 0.03mm, suitable for miniature vacuum devices. Functionally gradient alloy tubes utilize powder metallurgy or laser cladding to achieve a gradual change in composition between the inner and outer layers, balancing corrosion resistance and thermal conductivity. Surface coating technologies (such as platinum plating and nitriding) enhance the tube’s wear resistance and oxidation resistance, extending its service life by more than two times at temperatures of 1200°C. Furthermore, the promotion of intelligent manufacturing technologies, including online laser diameter measurement and eddy current testing, ensures dimensional accuracy and internal quality. Green production processes (such as chromium-free pickling and the use of recycled nickel) reduce environmental impact, increasing nickel recovery rates to over 90%. As vacuum electronic devices evolve toward higher frequencies and smaller sizes, demand for high-performance nickel and nickel alloy thin-walled tubes will continue to grow, driving the industry to achieve greater breakthroughs in material research and development and precision processing technologies.
