A critical review of ultrasound-assisted transient liquid phase bonding: From process mechanisms to material systems

Ultrasound-Assisted Transient Liquid Phase (U-TLP) Bonding represents a transformative advancement in joining technology, achieved by synergistically integrating high-frequency ultrasonic energy with conventional TLP bonding principles. This hybrid process induces profound changes in interfacial dynamics, enabling the rapid disruption of tenacious oxide layers, dramatic acceleration of atomic interdiffusion, and complete isothermal solidification within seconds to minutes-orders of magnitude faster than conventional TLP bonding. Consequently, U-TLP bonding effectively suppresses the formation of continuous brittle intermetallic compounds (IMCs), facilitating the formation of homogeneous, high-melting-point joints with mechanical properties comparable to the base metal, all in ambient air. This review provides a comprehensive and critical analysis of the U-TLP bonding process, delving into the fundamental mechanisms of ultrasonic cavitation, acoustic streaming, and acoustic softening responsible for enhanced oxide removal and accelerated kinetics. It systematically summarizes the application of U-TLP bonding across a wide spectrum of material systems, including lightweight alloys (Mg, Al), conductors (Cu, Ni), challenging dissimilar metal pairs, and ceramic-metal composite structures. This review not only summarizes progress but also critically assesses experimental constraints, inconsistent data, and methodological differences across studies, clarifying controversies in oxide removal mechanisms, diffusion kinetics, and process stability. We suggest integrating in-situ synchrotron radiation testing with multi-scale modeling in future work. This will facilitate the transformation of the empirical U-TLP bonding process into a well-designed technical system. Such advancements are essential to unlock its full potential for next-generation manufacturing in aerospace, electronics, and energy sectors.