How is superelastic nitinol tubing made?

Raw Material Preparation and Alloying

Selection of High-Purity Nickel and Titanium

The journey of creating superelastic nitinol tubing begins with the careful selection of raw materials. High-purity nickel and titanium are essential for achieving the desired properties of the final product. These elements are typically sourced from reputable suppliers who can guarantee the purity levels required for aerospace and medical-grade applications. The nickel and titanium are usually in the form of ingots or pellets, ready for the alloying process.

Precise Weighing and Mixing

Once the raw materials are procured, they undergo a meticulous weighing process. The composition of nitinol is critical, typically consisting of approximately 55-56% nickel and 44-45% titanium by weight. This precise ratio is crucial for achieving the superelastic properties that make super elastic nitinol tube so valuable. Advanced weighing equipment ensures accuracy down to fractions of a gram, as even slight deviations can significantly affect the final product's performance.

Vacuum Arc Remelting (VAR)

The weighed nickel and titanium are then subjected to the Vacuum Arc Remelting (VAR) process. This sophisticated technique involves melting the metals in a vacuum chamber using an electric arc. The vacuum environment prevents contamination from atmospheric gases, ensuring the purity of the resulting alloy. Multiple remelting cycles may be performed to enhance homogeneity and remove any residual impurities, resulting in a high-quality nitinol ingot ready for further processing.

Ingot Processing and Initial Shaping

Hot Working and Forging

The solidified nitinol ingot undergoes hot working processes to break down its as-cast structure and improve its mechanical properties. This typically involves heating the ingot to temperatures above 800°C and subjecting it to various forging operations. Hydraulic presses or specialized forging hammers apply controlled pressure to shape the ingot into a more manageable form, such as a bar or rod. This step not only refines the grain structure but also helps in achieving a more uniform composition throughout the material.

Extrusion and Drawing

To transform the forged super elastic nitinol tube into a tubular shape, extrusion and drawing processes are employed. The material is heated and forced through a die with a specific cross-sectional shape, creating a hollow tube. This initial extrusion is followed by a series of cold drawing operations, where the tube is pulled through progressively smaller dies to reduce its diameter and wall thickness. Each drawing step work-hardens the material, necessitating periodic annealing treatments to restore ductility and prevent cracking.

Precision Machining

In some cases, particularly for complex geometries or tight tolerances, precision machining techniques may be employed. Computer Numerical Control (CNC) lathes and mills can be used to refine the dimensions and surface finish of the nitinol tubes. This step is especially crucial for applications in the medical industry, where exact specifications are paramount. Electrochemical machining or laser cutting might also be utilized for creating intricate patterns or fenestrations in the tubing.

Heat Treatment and Final Processing

Shape Setting and Annealing

One of the most critical steps in producing superelastic nitinol tubing is the heat treatment process. The tubes are carefully fixture on specialized mandrels or forms that define their final shape. They are then subjected to precise heating cycles, typically at temperatures between 450°C and 550°C. This shape-setting process aligns the crystal structure of the nitinol, imparting its characteristic shape memory and superelastic properties. The duration and temperature of this treatment are meticulously controlled, as they directly influence the transformation temperatures and mechanical behavior of the finished product.

Surface Treatment and Passivation

After heat treatment, the super elastic nitinol tubes undergo surface treatments to enhance their performance and biocompatibility. Electropolishing is a common technique used to smooth the surface and remove any residual stresses or imperfections. This process not only improves the tube's corrosion resistance but also creates a uniform oxide layer that is crucial for biomedical applications. Following electropolishing, a passivation treatment may be applied to further enhance the stability of the oxide layer, ensuring long-term durability and safety when used in the human body.

Quality Control and Testing

The final stage in the production of superelastic nitinol tubing involves rigorous quality control measures. Each batch of tubes undergoes a battery of tests to verify its mechanical properties, dimensional accuracy, and surface quality. Tensile testing assesses the tubes' strength and elongation capabilities, while differential scanning calorimetry (DSC) is used to confirm the transformation temperatures. Non-destructive testing methods such as X-ray fluorescence spectroscopy and ultrasonic inspection ensure the material's composition and structural integrity. Only tubes that meet or exceed the stringent quality standards are approved for use in critical applications.

Conclusion

The production of super elastic nitinol tube is a complex process that combines metallurgical expertise with advanced manufacturing techniques. From raw material selection to final quality control, each step is crucial in creating tubes with the remarkable properties that make nitinol so valuable across various industries. As technology advances, we can expect further refinements in this process, leading to even more innovative applications for this extraordinary material.If you want to get more information about this product, you can contact us at: baojihanz-niti@hanztech.cn.