A new gasdynamical coating method using detonation tube technology

A 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. A specially designed particle feeder injects the particles into the quasi-steady nozzle flow (res. pressure 30 bar, res. temperature 3600 K) with variable position along the nozzle axis in order to control the particle temperature and particle velocity. Theoretical particle temperatures are close to or exceed the melting point of the particular material. Several measuring techniques including PIV have been applied to characterize the flow features of the process as well as the particle behaviour. First coating samples with different material pairings and excellent properties concerning microhardness and porosity have been obtained so far. Due to the variability of process parameters, this method shows high potential for optimization of coatings produced so far and for testing further new material pairings.