H. Liao, LERMPS-UTBM, Belfort, France; W. Y. Li, Northwestern Polytechnical University,, Xi'an, China; G. Zhang, C. Coddet, University of Technology Belfort-Montbeliard, Belfort Cedex, France; H. T. Wang, C. J. Li, School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an, China
Cold spray is an emerging coating process in recent years. It has attracted worldwide interest for the fast deposition of high-quality metallic coatings. Many investigators have examined this process by both experiment and numerical simulation on the processing parameters, microstructure and corresponding properties of the deposits. However, there are still some underlying problems to be clarified.
Therefore, in this paper, the effect of the main factors, involving the nature of accelerating gas and its operating pressure and temperature, and particle size was investigated numerically with a convergent-divergent nozzle. More attention has been paid on the influence of powder carrier gas on the accelerating gas flow and particle accelerating behavior. It was found that the nature of accelerating gas and its operation pressure and temperature, and particle size significantly influenced the particle velocity. Under a certain accelerating gas condition, with increasing both the pressure and temperature of powder carrier gas, the particle velocity has a little increase. With increasing the powder carrier gas temperature, the particle temperature also has a little increase. The experiment with Cu powder sprayed under different gas conditions confirmed the simulation results. This fact means that the optimization of cold spray process could be conducted using the numerical simulation method.
Cold spraying, as a new coating process, has attracted worldwide interest for its high deposition efficiency of high-quality metallic coatings. However, a high pressure gas is necessary to accelerate the spray particles to a high velocity through a convergent-divergent de Laval nozzle. Therefore, the gas flow rate is much higher than that used in the conventional thermal spray process. When helium is used as an accelerating gas, the cost will be relatively high.
In the present paper, a novel convergent-barrel nozzle was designed through numerical simulation based on the significant influence of particle temperature on its deposition behavior. The effects of the main factors, involving the length of barrel section, the nature of accelerating gas and its operating pressure and temperature, and particle size, were investigated numerically. It was found that the particles can achieve a relatively low velocity but high temperature under a relatively low gas pressure. Therefore, the gas flow rate was significantly reduced. The experiment results with Cu powder confirmed that the particles can be successfully deposited to form a dense coating under a low gas pressure and flow rate.
