The production process of tantalum tubes is a complex technology involving multiple precise procedures, which fully demonstrates the challenges of processing refractory metals. Due to its high melting point, high reactivity and significant tendency towards work hardening, the manufacturing of tantalum tubes requires specialized techniques and equipment.
The typical production process of tantalum tubes mainly consists of two technical routes: powder metallurgy and plastic processing, among which the latter is more common. If it is a solid bar, a hole needs to be drilled in the center to prepare "hollow billets" for the subsequent pipe rolling. Heat the drilled billets at high temperatures. Due to the high deformation resistance of tantalum, it is usually necessary to heat it above the recrystallization temperature (for example, 1000°C - 1300°C). The surface of the heated billet is coated with a special layer of glass lubricant to reduce the friction between the billet and the die during the extrusion process, and to play a role in heat insulation and oxidation prevention. The preheated and lubricated billet is placed into the die of the extruder. Under tremendous pressure, it is extruded from the annular die to form a longer and thinner tube (extruded tube). This is the first major deformation process. Surface treatment includes sandblasting and pickling (usually using a mixture of hydrofluoric acid and nitric acid) to remove the oxide scale, residual glass lubricant and defects on the surface. A smooth and clean surface is crucial for subsequent cold rolling, and any surface defects may be magnified during the rolling process.
Cold rolling (core forming process) is a precision control process that further thins and elongates tantalum tube billets to achieve the target size. The most commonly used method is tantalum tube rolling. The tube blank is rolled by a roller with a conical core head, which compresses it radially, reduces the wall thickness and increases the length. Tantalum hardens rapidly during cold working, with its strength and hardness increasing and its plasticity and toughness decreasing. Multi-pass cycle: Therefore, cold rolling cannot be completed in one go and must adopt the cycle mode of "rolling - annealing - rolling". After each large deformation rolling, intermediate annealing is required to restore the plasticity of the material. And the purpose is to eliminate the work hardening caused by cold rolling, cause recrystallization of the material, restore its plasticity and toughness, so as to carry out the next cold working. The purpose of intermediate annealing is to eliminate the work hardening caused by cold rolling, cause recrystallization of the material, restore its plasticity and toughness, and facilitate the next cold working process.
To place the outer tantalum tube in a high vacuum environment, it must be done under high vacuum conditions (usually better than 10-3 Pa). Tantalum is highly prone to react with oxygen, nitrogen and other substances at high temperatures, causing the material to become brittle (hydrogenation, nitriding, oxidation). The precise temperature-controlled annealing temperature is usually controlled above the recrystallization temperature (for example, 1000°C - 1200°C), and the specific temperature and time depend on the desired grain size and performance requirements.
When the pipe size approaches the target value, it enters the finishing stage. Drawing or other precision rolling methods may be used to fine-tune the diameter and wall thickness of the pipe to ensure dimensional accuracy and surface finish. The final annealing of the finished product is determined based on the performance requirements of the final product (whether it is in a hard state, semi-hard state or soft state). For instance, soft pipes that require high plasticity must be fully annealed. Precise straightening and cutting are carried out, and then cut to a fixed length.
