# Features of the Structural Design of Welded Joints of Superelastic Nitinol Wires

## TL;DR

This paper studies the best ways to weld superelastic nitinol wires, finding that capacitor discharge welding shows promise for creating strong, functional joints.

## Contribution

The study introduces capacitor discharge welding as a promising method for joining thin nitinol wires with minimal structural changes.

## Key findings

- TIG welding preserves the microstructure and superelastic properties of nitinol joints under proper argon protection.
- Capacitor discharge welding produces joints with TiNi + TiNi3 eutectics and good shape recovery, showing potential for thin nitinol wires.
- PAW welding causes oxide formation and brittle fractures due to Ti2Ni inclusions, making it less suitable for nitinol joints.

## Abstract

The object of the study is a permanent joint of thin wires made of nitinol alloy. The problem of ensuring the formation of a joint of wires made of nitinol alloy was solved based on minimising changes in the structure of the welded joint material relative to the materials being joined. The properties of the welded joint material of the nitinol were studied using scanning electron microscopy and micro-X-ray spectral analysis. The studied permanent joint was obtained by TIG, microplasma (PAW) and capacitor discharge (CDW) welding. It was found that TIG welding can ensure the proximity of the microstructures of the wire and welded joint materials under conditions of sufficient protection in an argon atmosphere. Such TiNi welded joints have a welded joint material that retains its superelastic properties (within the limits of the shape memory effect). Capacitor discharge welding allows the joint to be brought closer to the required level of microstructure of the weld material. The results of mechanical tests demonstrated the limited capabilities of joints made of thin nitinol wires. At the same time, the appearance of only newly formed TiNi + TiNi3 eutectics in the weld material and a sufficient level of restoration of the welded joint shape give reason to consider capacitor discharge welding promising for joining thin nitinol wires. PAW leads to the formation of a significant amount of oxides in the weld and an increase in the number of Ti2Ni inclusions, which leads to brittle fracture of the welded joint even at low degrees of deformation. The results of the study can be used, in particular, for the manufacture of nitinol wire joints in medical devices.