ADVANCED JOINING TECHNIQUES FOR MULTI-MATERIAL STRUCTURES: A REVIEW ON ULTRASONIC CONSOLIDATION, COLD SPRAY, AND ELECTRON BEAM MELTING

The demand for lightweight, high-performance, and multifunctional structures has driven rapid advances in multi-material joining technologies across aerospace, automotive, and electronics industries. Traditional joining methods often struggle with challenges such as thermal distortion, brittle intermetallic formation, and residual stresses when bonding dissimilar materials. This review critically examines three advanced additive manufacturing techniques—Ultrasonic Consolidation (UC), Cold Spray (CS), and Electron Beam Melting (EBM)—that offer promising solutions for multi-material fabrication. The mechanisms, material compatibility, microstructural evolution, and mechanical performance of joints produced by each process are systematically discussed. UC and CS, as solid-state processes, minimize thermal damage and oxidation, enabling strong joints between metals with dissimilar properties. EBM, operating in a high-vacuum environment, allows precise control over microstructure and enables the fabrication of complex, high-performance components. The novelty of this review lies in its integrative comparison of solid-state and fusion-based techniques, with a specific focus on their effectiveness in multi-material structural applications. It emphasizes interface behavior, residual stress development, and scalability challenges, while highlighting underexplored directions such as hybrid processing, interface engineering, tailored material feedstocks, and in-situ monitoring strategies. However, challenges such as bonding efficiency, residual stress management, and scalability remain. Future research directions are proposed, including process optimization, interface engineering, expanded material libraries, and integrated real-time monitoring to fully realize the potential of these emerging technologies for multi-material structural applications.