Transient interfacial melting promotes bonding in cold spray additive manufacturing of dissimilar metals

Understanding supersonic impact-induced bonding between dissimilar metals is important for advancing solid-state multi-material manufacturing. While established bonding mechanisms are typically based on plasticity-related indices and are defined for materials with similar properties, here we uncover a hidden dimension of thermo-dynamic mechanisms driving impact-induced bonding of mismatched metals. Atomic-scale simulations reveal transient melting initiating at the substrate surface upon impact and rapidly propagating across the interface. STEM-EDX analysis identifies an oxygen-rich interfacial layer (∼17–20 nm), more than twice as thick as the native oxide, with SAED confirming new oxide formation. Band-shaped segregations within the Impact-Affected Zone (IAZ), ultrafine subgrains (∼100 nm), and alloy-enriched precipitates adjacent to the IAZ are also observed. Together with the simulation results, these features are consistent with transient interfacial melting followed by rapid re-solidification. These findings highlight melting, rapid re-solidification, and the resulting microstructural transitions as significant contributors to metallurgical bonding in mismatched metallic systems, representing a thermodynamic pathway distinct from the widely accepted plasticity-based mechanisms. These insights advance the understanding of dissimilar-material joining and support the development of next-generation additive manufacturing technologies.