Insight into the role of interparticle bonding on tensile properties of cold spray additively manufactured copper

Cold spray additive manufacturing (CSAM) often yields metal components with suboptimal mechanical properties, primarily poor ductility, stemming from inadequate inter-particle bonding. This work overcomes this limitation by using a homemade helium circulation cold spray (CS) system to fabricate copper deposits that exhibit a superior strength-ductility synergy (ultimate tensile strength: 372 MPa, elongation: 14.2%) in their as-sprayed state. The system's efficacy is attributed to the superior acceleration provided by helium and an inert deposition environment that prevents powder surface oxidation. We systematically investigated the origins of these enhanced properties by examining interparticle bonding, work hardening, recrystallization, and twinning. Our analysis establishes correlations among CS parameters, particle impact velocity (V_p) and temperature (T_p), the dimensionless parameter η (V_p/V_cr), and the resulting tensile properties. It was found that a higher η value does not necessarily correspond to higher strength or ductility. The findings reveal that high V_p (facilitated by helium) induces greater deformation of copper (Cu) particles and formation of a nanocrystalline interface layer at deformed splats. Conversely, while high T_p promotes dynamic recrystallization and twinning, it simultaneously intensifies surface oxidation, leading to deleterious oxide films at splat boundaries that degrade bonding and ductility. This research highlights the paramount importance of optimizing impact conditions to strengthen interparticle bonding and mitigate oxidation for high-performance CSAM components.