Determination of the structural features of joint material of the nitinol wires made by laser welding

The object of the study is the welded joint of thin wires made of nitinol alloy. The problem of ensuring the formation of a joint of wires with a diameter of 0.8 mm made of nitinol alloy was solved based on determining the influence of laser welding modes on structural changes in the material of the weld. Based on the use of scanning electron microscopy, micro-X-ray spectral (EDS) analysis, a study of the properties of the material of the welded joint of the nitinol wires was performed. The joint was obtained by welding with an ytterbium fiber laser. It was confirmed that laser welding in an argon atmosphere is able to ensure the high-quality formation of a welded joint without macrodefects while maintaining the superelasticity of the joint material (within the shape memory effect). Two laser welding modes were used with a constant applied laser radiation energy. The duration of the laser radiation action and the multiplicity of such action were varied. At the same time, structural changes in the weld material, which are caused by the multiplicity of laser heating, involve the formation of enlarged zones of the eutectic TiNi + TiNi3 from metastable nanophases of titanium nickelides. The number of such grains decreases with the depth of the weld. Detection of structural changes and establishment of a decrease in the number of point phase inclusions with an increased nickel content in the weld can be a regulating factor for optimizing the structure of the welded joint material. In the welded joints made, when it is bent at an angle of 30°, the residual deformation does not exceed 10%. The results of the study of the structure of the welded joint of nitinol wires made by laser welding are promising and can be used in the conditions of manufacturing nitinol wire connections by welding medical products