Strength and Phase Identification of Autogenous Laser Brazed Dissimilar Metal Microjoints

The continued advancement of implantable medical devices has resulted in the need to join a variety of dissimilar, biocompatible metal pairs to enable selective use of their unique properties. Typical materials used in implantable medical devices include stainless steel (SS), titanium, platinum (Pt), as well as shape memory materials such as NiTi. Joining these dissimilar metal pairs, however, often results in excessive formation of brittle intermetallics, which significantly reduce the strength of the joints. The use of filler materials to combat the formation of intermetallics, however, results in reduced biocompatibility. Autogenous laser brazing is a novel process that is able to form thin, localized joints between dissimilar metal pairs without filler materials. In this study, the formation of autogenous laser brazed joints between NiTi and SS wires is investigated through experiments and numerical simulations. The strength, composition, microstructure, and phase formation of the resultant joints are investigated as a function of processing parameters and thermal, fluid flow, and phase prediction simulations are used to aid in understanding the joint formation mechanism.