Friction stir welding and additive friction stir deposition of high entropy alloys: A review

High-entropy alloys (HEAs), composed of multiple principal elements, exhibit excellent mechanical properties, thermal stability, and resistance to phase transformations. However, their complex microstructural behavior challenges conventional processing and welding. This review summarizes recent advances in friction stir welding (FSW) and additive friction stir deposition (AFSD) of HEAs, focusing on microstructural evolution and mechanical performance. FSW promotes grain refinement with dynamic recrystallization, producing fine and homogeneous structures. Process parameters strongly affect heat input, where lower input improves the strength–ductility balance, while excessive input causes grain coarsening and property degradation. AFSD also enables grain refinement and strength enhancement through recrystallization and phase evolution. Further optimization and deeper understanding of phase evolution are required for broader industrial application.