Numerical studies on cold spray gas dynamics and powder flow in circular and rectangular nozzles

Cold Spray (CS) is an emerging metal additive manufacturing and surface coating technology, where metallic microscale powders are accelerated to supersonic velocities followed by impact onto a target substrate. In CS, the design of the cold spray nozzle is the pillar, determining the efficacy and quality of the deposited layers as it both affects the gas dynamics and powder flow. However, comparative studies on the gas-powder flow dynamics within different nozzle profiles are limited. In this paper, two prominent CS nozzle exit profiles – circular and rectangular – are extensively studied using numerical modeling by considering both soft and hard feedstock powders (i.e., tin (Sn) and copper (Cu)). In this regard, computational fluid dynamics (CFD) simulations are performed to investigate the effect of inlet gas pressure and temperature on supersonic jet formation and powder dispersion characteristics. In regard to the gas flow, the rectangular nozzle showed flow separation much earlier in the nozzle compared to the circular nozzle under the same process settings. Notably, this phenomenon was found to be more drastic at lower gas pressures. As for the powder flow, it was observed that the rectangular nozzle is less effective at accelerating powders compared to the circular nozzle but allows for powders to reach higher temperatures. Moreover, particle deposition experiments on a composite substrate (GFRP) revealed that while the rectangular nozzle produced more uniform particle deposition (Ra = 8.12), it led to a thinner metal coating (≈53 %) with significantly higher electrical resistance (143-fold) compared to the circular nozzle. The results provide valuable insights into understanding the advantages and limitations of both the circular and rectangular nozzle profiles in CS, contributing to more efficient and high-quality particle deposition.