High-Strength Dissimilar Welds Between a NiTi Shape Memory Alloy and Titanium Obtained by Intermixing Niobium Using Pulsed Laser Beam Welding

Abstract

Joining of NiTi shape memory alloys with commercially pure titanium (Ti) is of great interest for manifold industrial applications. However, dissimilar fusion welding of these materials is associated with the formation of extremely brittle intermetallic compounds, e.g., Ti2Ni and TiNi3, which drastically limit the mechanical properties of NiTi/Ti joints. The present investigation seeks to improve both chemical compatibility and mechanical performance through intermixing of a niobium foil as filler material into a NiTi/Nb/Ti butt-joint configuration by means of pulsed laser beam welding. Different pulse durations are applied to tailor intermixing and evaluate the deviating chemical compositions of the weld metal. It is demonstrated that intermixing of niobium significantly increases the weldability of the material combination NiTi/Ti compared to autogenous welding. However, the proportion of intermixed filler material exerts a substantial impact on the microstructural evolution and mechanical properties. Ultimate tensile strengths of up to 679 MPa with fracture occurring in the titanium base metal at an elongation at break of 18.7 pct is obtained by a reduction of the pulse duration, which represents a major improvement over previous studies focusing on fusion welding of NiTi to titanium and its alloys.