Nozzle geometry has a profound effect on HVOF spraying, influencing combustion gas dynamics as well as particle behavior. Nozzle dimensions are also important in cold gas-dynamic spraying (CGDS), particularly the length of the nozzle which affects gas flow temperature and speed. In this study, numerical simulations and experiments were conducted to determine how the length of the entrance convergent section of gun nozzles affects HVOF spraying. Process changes that occur inside the nozzle (as predicted by simulation) were correlated with coating properties. An Al2O3-TiO2 powder was used for the experimental studies. Changes in nozzle length had a significant impact on deposition efficiency, microstructure, hardness, and particle velocity. These relationships (as measured and calculated) were then applied to the nozzle design for the CGDS method.

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