Dual role of oxides and a new bonding mechanism in cold spray involving dissimilar metals

Cold spray (CS) is an emerging technology offering appealing benefits for many industrial applications, including additive manufacturing, coating, and on-site repair. Successful application of the CS process relies on accurate understanding of the bonding mechanisms, for which oxides play a critical role. Combining detailed experimental work and numerical simulations on base of peridynamics, the role of oxides during cold spraying of Cu particles onto an Al substrate was investigated, as a representative CS scenario involving dissimilar metals. Significant deformation disparity was observed during the impact process, resulting in preferential removal of Al₂O₃, while fragmented Cu oxides largely remain at the interface. The residual oxides can act as barrier preventing metallurgical bonding. Yet, interesting, they may also serve as constituents for thermite reactions, triggered by impact-induced ignition, to produce interfacial bonding in the form of new, compact and well-bonded thin amorphous oxides. This study, for the first time, reveals the dual role of oxides, acting as both a barrier preventing metallurgical bonding and a constituent for thermite reaction to promote bonding during the CS deposition. The findings provide new mechanistic knowledge critical for understanding the bonding and deposition in CS of dissimilar metals and suggest new design possibilities utilizing thermite reaction to enhance the CS process.