Generation of high particle velocities by detonation tube technology with respect to coating techniques
Final Report Abstract
This report presents the final status of the research in the generation of high particle velocities for coating technique. A new detonation driven spray technique in which particles are accelerated in a high enthalpy nozzle flow has been designed and successfully tested. Particle velocities in the average between 1500 m/s and 1800 m/s are achieved. In conventional thermal spray applications the maximum particle impact velocities are about 1000 m/s. Depending on the spray material and size, only spray material with a critical bonding velocity lower than 1000 m/s can be used in these applications. Furthermore, the coating quality increases when the impact velocity is close to the upper erosion velocity. Therefore, higher particle impact velocities extend the application range and lead to a better coating quality with very low porosity, high bonding strength and hardness. This method uses the detonation driven shock tunnel technology to operate a nozzle in an intermittent process with a frequency up to 5 Hz. High reservoir conditions are generated by the detonation of hydrogen (stoechiometric with oxygen). The particles are injected into the nozzle flow downstream of the nozzle throat after the nozzle flow is fully established. Several measuring techniques including PIV have been applied to characterize the flow features of the process as well as the particle behavior. The coating samples produced by this facility have been analyzed by the Surface Engineering Institute (IOT) of RWTH Aachen and demonstrate that this new technology can provide very dense coating layers with low porosity and high micro-hardness. The experiments performed clearly show that the detonation driven shock tunnel technology allows achieving much higher particle velocities than the conventional thermal spray methods. Correspondingly the coating samples indicate a higher quality concerning microhardness and structure. As the higher particle velocities and also elevated particle temperatures, achieved by this new technique, extend the application range of thermal spray, it is recommended to test many different material pairings (especially ceramics, compounds and hard metals) and to perform more investigations of the influence of spraying parameter on the quality of coatings already obtained.
Publications
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Flow characterization of a detonation gun facility and first coating experiments, Journal of Thermal Spray Technology, 2014
C. Henkes, and H. Olivier
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Particle acceleration in a high enthalpy nozzle flow with a modified detonation gun, Journal of Thermal Spray Technology, 2014, 23(4), p 625- 640
C. Henkes, and H. Olivier
