Similar and Dissimilar Joining of Nitinol Through Transient Liquid Phase Bonding

Similar and dissimilar joining of shape memory/super elastic materials have gained increased attention in recent years. However, traditional joining methods are challenging to apply to these materials because they lead to the formation of brittle intermetallics, decreases in functional performance, and strength reductions. Here, transient liquid phase (TLP) bonding is being studied as a viable solution for dissimilar joining. Few hundred nanometers to several micron-thick magnetron sputtered interlayer foils, with one or more layers of different compositions in the NiTiNb system, were designed via CALPHAD approaches to join NiTi with both NiTi and Titanium - systems known to form brittle phases during traditional fusion welding. Upon heating, the layers interdiffuse to form either a partial or complete low-melting transient liquid, which fills the gap between the surfaces being bonded. The designed composition allowed for phase control during the bonding process, while the nanostructured interlayers allowed for short diffusion length scales.