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 copper and titanium powder was used in the experiments. Working gas (is nitrogen) pressure and temperature at nozzle-intake were 3MPa and 623K, respectively. In addition, the change in the nozzle contour and the change in the entrance 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 properties. Deposition efficiency of both copper and titanium increase with increasing the length of the convergent section of the nozzle.

Wear properties of WC/Co cermet coatings have been investigated prepared by cold spraying. Influence of cobalt contents (12~25wt.%), WC particle size (0.2 and 1.8 µm) and agglomerated-and-sintered powder size (-20+0 and - 45+15 µm) on abrasive wear resistance, micro hardness and coating structure is studied, in detail. It has been found that both smaller WC particle and decrease of cobalt content are effective to produce dense, hard and highly wear resistant coating. Smaller powder size is also favorable to make a coating with high mechanical properties. As a result, the cold sprayed coating from WC(0.2 µm)/12wt.%Co with powder size of -20+0 µm has best mechanical properties within this study. This coating has high uniformity and high density with little pores compared to conventional HVOF sprayed coatings. Abrasive wear resistance of the cold sprayed coating, investigated using Suga-abrasion tester, has been almost comparable to HVOF sprayed coating prepared from same feedstock. Strong correlation is also seen between Vickers hardness and abrasive wear resistance. Microstructural analysis suggests that further improvement of coating uniformity by decrease of small pores with the size of sub micron and homogeneous dispersion of WC grains in the cobalt matrix is required to improve the mechanical properties.