DISSERTATION DEFENSE
Brayden Terry, Interdisciplinary Materials Science
*under the supervision of Al Strauss
鈥淔riction Stir Welding of Thin Sheet Nitinol: Dissimilar Materials and Heat Treatment鈥�
3.25.26 | 9:00 am | 132 Olin Hall|
Friction stir welding (FSW) is a solid-state joining method that sees use in the aerospace, automotive, rail, maritime, and tech industries. Nitinol, or NiTi, is perhaps the most well-known shape memory alloy with applications found in biomedical, aerospace, defense, robotics, automotive, tech, and many other industries. This widespread use is due to its excellent mechanical properties, biocompatibility, corrosion resistance, and, most famously, its unique properties 鈥� the shape memory effect and superelasticity. Currently, traditional fusion welding methods show lackluster performance when applied to NiTi alloys due to their high sensitivity to compositional changes and complex microstructural developments with thermomechanical processing. This naturally leads to the need for a reliable joining process to help develop applications for nitinol and encourage production of complex geometries. As a solid-state process, FSW is known for its capability to join sensitive alloys like NiTi with minimal disruption to local compositions and pre-existing thermal treatments. This dissertation serves to further the intersectional knowledge of FSW and NiTi. Dissimilar FSW between NiTi and common aerospace aluminum alloys was demonstrated with joint efficiency and mechanical properties varying based on alloy selection. Dissimilar FSW of NiTi and Ti-6Al-4V was performed with microstructural developments examined. Growth of interfacial intermetallic compounds was found to degrade the joint. Finally, post-weld heat treatment of NiTi showed improvement in joint performance with dependence on time and temperature. Heat treatment successfully returned shape memory performance to pre-weld conditions. These studies demonstrate FSW as a capable joining method for extended applications of NiTi.