Effect of gun nozzle geometry, increase in the entrance convergent section length and powder injection position on cold sprayed titanium coatings

Nozzle geometry influences gas dynamics, such as gas density, velocity and temperature, making sprayed particle behavior one of the most important parameters in cold spray process. Gas flow at the entrance convergent section of the nozzle takes place at relatively high temperature and are subsonic. Thus, this region is a very suitable environment for heating spray particle. In this study, numerical simulation and experiments were conducted to investigate the effect of nozzle contour (convergent -divergent and convergent-divergent-barrel), entrance geometry of convergent-divergent nozzle and powder injection position at nozzle on the cold spray process. The process changes inside the nozzle were observed through numerical simulation studies and the results were used to find a correlation with coating properties. A titanium powder was usedin the experiments. Working gas (is nitrogen) pressure and temperature at nozzle-intake were 3MPa and 626K, respectively. In addition, the change in the nozzle contour and the change in the convergent section length of the gun nozzle were found to have a slight effect on the coating microstructure. Powder injection position was also found to influence deposition efficiency and coating porosity with titanium powder. Deposition efficiency using axial injection was found to be higher than that using radial injection.