Ductile and high strength Cu fabricated by solid-state cold spray additive manufacturing

• Pure Cu shows the UTS of 271 MPa and elongation to fracture of 43.5% without additional post-treatments. • Cold spray additive manufacturing can achieve combination of high strength and good ductility • The deposit microstructure shows a gradient nano-grain structure with bimodal size distribution. • The gradient nano-grained (GNG) structure in single splat composes the deposit microstructure. • The balance between work hardening and thermal softening determine the performance. In this work, pure Cu with excellent strength and ductility (UTS of 271 MPa, elongation to fracture of 43.5%, uniform elongation of 30%) was prepared using cold spray additive manufacturing (CSAM), realizing a breakthrough in the field. An in-depth investigation was conducted to reveal the microstructure evolution, strengthening and ductilization mechanisms of the CSAM Cu, as well as the single splats. The results show that the CSAM Cu possesses a unique heterogeneous microstructure with a bimodal grain structure and extensive infinitely circulating ring-mounted distribution of twinning. Based on the single splat observation, the entire copper particle forms a gradient nano-grained (GNG) structure after high-speed impact deposition. The GNG-structured single splat serves as a unit to build the heterogeneous microstructure with bimodal grain distribution during the successive deposition in CSAM. The results also show that CSAM can achieve synergistic strengthening and ductilization by controlling the grain refinement and dislocation density. This work provides potential for CSAM technique in manufacturing various metallic parts with the desired combination of high strength and good ductility without additional post-treatments.