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2873 |
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Tuesday, September 27, 2011, Saal B2.1 2:50 PM Cold Spraying 1 |
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Investigation on the effect of helium-to-nitrogen ratio as propellant gas mixture on the processing of titanium coating using cold gas dynamic spray and nozzle design optimization |
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Eric Irissou* / National Research Council Canada
- Industrial Materials Institute, CANADA Florin Ilinca / National Research Council Canada Industrial Materials Institute, CANADA Wilson Wong/ Mining and Materials Engineering Department - McGill University, CANADA Marie-Lise Tremblay/ National Research Council Canada Industrial Materials Institute, CANADA Jean-Gabriel Legoux/ National Research Council Canada Industrial Materials Institute, CANADA Stephen Yue/ Mining and Materials Engineering Department - McGill University, CANADA |
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In cold gas dynamic spray, the propellant gas velocity plays a crucial role since it governs the particle acceleration and particle impact velocity. Gas velocity is regulated by the nozzle design and the gas density. However, due to particle-shock-wave interactions, which reduce deposition efficiency and overall coating quality, there are limitations in the nozzle design Mach number. Therefore, to further increase the propellant gas velocity and consequently the particle velocity, it is necessary to increase its speed of sound. This can be achieved by either pre-heating the gas or by using a gas with a lower molecular mass, typically changing from nitrogen (N2) to helium (He). For some materials such as titanium it is very difficult to obtain fully dense coatings with N2 even at a high pre-heating gas temperature, so, using He is necessary. However, He is rare and expensive so its usage and consumption need to be optimized. This paper reports on the influence of the He to N2 ratio on the properties of cold sprayed titanium coatings and on the characteristics of the generated supersonic two-phase flow. Experiments were carried out varying the He to N2 concentration ranging from pure He to pure N2. Samples were characterized by their microstructural properties and adhesive strength. Deposition rate was evaluated and particle velocities were measured for all conditions. Velocity data were used to validate a computational fluid dynamic model. For several He to N2 concentration conditions, this model was used to calculate the optimal nozzle dimension (Mach number) for obtaining the maximum particle velocity. The performance of one optimum nozzle design was compared with the models results. |