Characterisation of Laser Welds, between Nitinol and Stainless Steel Wires

Nickel-Titanium (NiTi) shape memory alloys are often used in medical component devices, for instance as guide wires for neurological surgery applications. Manufacturing of such devices becomes more and more challenging, especially considering the need to join them with other metals, like Stainless Steel (SS). Laser welding is a promising technique to realize and to guaranty the mechanical stability of dissimilar metal welds. However, inherent differences in chemical compositions may lead to fracture of the weld due to the formation of brittle intermediate phases, such as TiFe or TiFe2. So it is important to characterise microstructure in a very efficient way. Both, pulsed Nd:YAG and continuous fibre laser were experimented to produce sound welds with sufficient tensile strength. Transmission (TEM) and Scanning Electron Mi- croscopy (SEM) were used to observe microstructure. Diffraction and Energy Dispersive Spectrometry (EDS) were used to determine phase structure and composition.