Friction Stir Welding of Dissimilar Materials: A Comprehensive Study on Joining Stainless Steel to Ni, Ti, and NiTi Alloys

Friction Stir Welding (FSW) has emerged as a transformative solid-state joining technology, overcoming the metallurgical hurdles inherent in conventional fusion welding. By operating below the melting point of the base materials, FSW suppresses solidification defects, minimizes thermal distortion, and prevents elemental volatilization, critical factors for high-performance alloys. This study provides a comprehensive investigation into the FSW of stainless steel joined to dissimilar non-ferrous systems: Nickel (Ni), Titanium (Ti), and Nickel-Titanium (NiTi) shape memory alloys. The research evaluates the microstructural evolution and the diffusion-controlled kinetics, grain refinement through dynamic recrystallization, and the kinetics of interfacial intermetallic compounds (IMCs). A strategic assessment using SWOT analysis is employed for each material system to identify technical strengths, such as the preservation of the superelastic plateau in NiTi joints and the achievement of tensile strengths exceeding 1100 MPa through post-welding treatments. Furthermore, the study clarifies the phenomenological conditions for the 1 μm Fe-Ti reaction layer threshold, establishing its applicability for thin-gauge structural integrity. By synthesizing current advancements in tool geometry and thermal management, this work highlights the potential of FSW for advanced multi-material applications in the aerospace and biomedical sectors, providing a roadmap for overcoming the rheological and chemical challenges of joining reactive, high-melting-point alloys within contemporary manufacturing frameworks.