Development of a manufacturing process for seamless nitinol tubes

The most commonly used SMA in medical technology is NiTi, known as Nitinol, which is a binary nickel-titanium alloy. Nitinol has been used in medical applications for the past decades due to its pseudoelastic properties and good biocompatibility. Also, NiTi shows a good ductility, which makes cold work possible – a necessary feature to control the microstructure.

The material in its final shape is in direct and often invasive contact with the patient, e.g. as stents. Laser-cut stents are made of drawn tube in different sizes and wall thicknesses. A very important aspect for the cyclic durability of long-term, high cycle implants like stents is the size of inclusions and impurities like carbides and oxides. At SMST 2023, a production approach for small-inclusion ingots was presented. A microstructure with very small inclusions (average inclusion size in the ingot is <5µm) allows the development of a customized processing route for tube processing. In this research work, we show our results on the development of a processing route for nitinol tubes made of these small-inclusion ingots. The aim is to produce seamless tubes with different diameters and wall thicknesses, taking into account the shape and distribution of the inclusions and how they affect our processing parameters. The control of the processing parameters during production is essential to achieve the required mechanical and functional properties.