In-Situ Phase Evolution of Sputtered Reactive Multilayers

The potential application and the commercial development of NiTi shape memory alloys (SMA) have been limited by the difficulties of joining these materials in both similar and dissimilar joints to other alloys as Ti6Al4V and AISI316LN (for biomedical applications). The possibility to join SMA to other materials would enlarge their fields of application. The temperature of the martensitic transformation is strongly dependent on the chemical composition and thermal cycles, thus fusion welding irreversibly affects the mechanical behaviour of these alloys. Recent advances have been reported where Nd/YAG laser has been applied successfully but research is still required to minimise the thermal impact on the material. The use of the self-propagating nature of some nano-multilayer reactions constitutes a powerful alternative for joining SMA in similar joints or to other alloys. So, a new approach for joining SMA using nanolayers from systems with high/medium energy of reaction is aimed. Before using them for joining purposes, phase evolution with temperature should be studied. Therefore, in-situ high temperature synchrotron-radiation X-ray diffraction and reflectivity measurements of low (Ni/Ti) and high energy (Pd/Al) multilayer thin films with different periods were performed. In-situ high resolution X-ray diffraction data, giving the phase evolution sequence with temperature of the different multilayer thin films under study is presented. A correlation between the multilayer design (system and period) and the tendency for intermetallic phase formation is established.