Influence of Carrier Gas Selection and Post-Heat treatment on the Microstructure and Mechanical Properties of Low-Pressure Cold Spray Copper

This study investigates the effects of N2 and He process gases, along with heat treatment, on the microstructure and mechanical properties of 3D-printed pure copper using a low-pressure cold spray system. Microstructural analysis, performed via X-ray diffraction and optical microscopy, and mechanical testing, including hardness and tensile tests, reveal key differences between the two gases. The N2-processed sample, which required more deposition passes, demonstrated enhanced plastic deformation, higher dislocation density, and lower porosity compared to the He-processed sample. This resulted in a microhardness of 112 HV for the N2 deposit, 1.3 times higher than the He deposit. Both deposits initially showed brittle failure and limited ductility, with tensile elongations under 0.2% and tensile strengths of only 70 MPa and 68 MPa for N2 and He samples, respectively. However, heat treatments at 500 °C and 700 °C improved mechanical strength and ductility, particularly at 700 °C, which effectively eliminated non-bonded interfaces and increased spheroidized voids. Post-heat treatment tensile strengths increased to 213 MPa and 193 MPa, with elongations of 28% and 25% for the N2 and He samples, respectively. These results suggest that N2, when used with appropriate deposition parameters and annealing, is a cost-effective alternative to He for cold-spraying copper.