Enhancing Ni–Ti shape memory alloy diffusion bonding with Ti/Ni reactive multilayer foils

This study investigates the utilization of Ti/Ni reactive multilayer foils as an energy source for facilitating the joining of Ni–Ti shape memory alloys through diffusion bonding. Multilayered samples were prepared using a 10-cycle accumulative roll bonding (ARB) process to be used for the bonding process. Diffusion bonding employing reactive multilayers was conducted over a temperature range of 600 °C to 900 °C, at 5 MPa pressure, with a 1-h hold time. Additionally, a comparison was made with a diffusion-bonded Nitinol sample at 900 °C without a reactive multilayer. Materials characterization and testing involved scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), shear strength testing, and differential scanning calorimetry (DSC), which were conducted on the bonded samples. The findings underscored the advantages of using reactive multilayers for diffusion bonding. These benefits included the formation of TiNi and the induction of a shape memory effect in the joint region, alongside a 1.5 times shear strength compared to identical diffusion bonding conditions without reactive multilayers. Moreover, employing reactive multilayers in the diffusion bonding of Nitinol holds promise for significantly reducing the energy needed to achieve robust and seamless bonded boundaries in the joining area.