Impact of beam oscillation and power modulation on the intermixing behavior of dissimilar titanium/niobium/nitinol joints during micro electron beam welding

Abstract

The present study seeks to expand the knowledge on dissimilar fusion welding of the material combination NiTi/Nb/Ti by investigating micro electron beam welding in a butt-joint configuration. In addition to adapted power modulation, a novel approach of utilizing the process-inherent fast beam oscillation is applied to improve the melting and intermixing behavior of the comparatively high-melting Nb filler material. Two different Nb thicknesses, measuring 0.2 and 0.4 mm, are implemented and compared with regard to weldability and microstructural evolution in the weld metal. It is demonstrated that the welding experiments are associated with major challenges due to the considerable differences in melting temperature and thermal conductivity of the base and filler materials, resulting in inhomogeneous elemental distribution and welding defects. Nevertheless, the welded joints exhibit excellent mechanical properties under quasi-static tensile load, which can be attributed to a reduced formation of Ti₂Ni intermetallic compounds due to the intermixing of Nb. Ultimate tensile strengths of up to 673 MPa and elongations at break of 6.9% are achieved, demonstrating that micro electron beam welding is a promising process to produce high-strength dissimilar NiTi/Nb/Ti joints.