Bi-modal structured cold spray copper deposits enabling high strength and ductility

• Cold spray additive manufacturing using nitrogen produces copper with a bimodal grain structure. • The resulting Cu deposits exhibit both high strength (327 MPa) and ductility (18%). • A novel coordinated deformation mechanism performed by growing nanocrystalline grains and rotating microcrystalline grains. • Back stress from strain incompatibility in bimodal grains promoted hardening and coordinated deformation. • At later deformation stages, the mechanism shifted to dislocation-dominated, resulting in grain fragmentation. Cold Spray Additive Manufacturing (CSAM) using nitrogen as a carrier gas enables the fabrication of bulk copper with a unique bi-modal grain structure. This structure, composed of nanocrystalline grains surrounding microcrystalline grains, delivers an exceptional combination of high strength (ultimate tensile strength of 337 MPa) and notable ductility (elongation to failure of 16.2 %). In-situ tensile testing coupled with EBSD reveals that coordinated deformation mechanisms: grain growth in nanocrystalline regions and rotation in microcrystalline grains, enable strain accommodation and delay failure. As deformation progresses, the plastic deformation mechanism transitions to one dominated by dislocation nucleation and accumulation within both nanocrystalline and microcrystalline grains. This shift leads to the fragmentation of nanocrystalline grains and further refinement of microcrystalline grains, resulting in a substantial increase in strain concentration until failure.