Wire arc spraying has traditionally filled metallic coating needs for low end users, while higher quality coatings required the use of higher cost systems. A new high velocity wire arc spray device has been developed through a NASA SBIR project whose high particle velocity capabilities could provide high quality coatings while keeping costs well below those associated with HVOF and plasma spray approaches. In addition, this technique achieves these high velocities in an extremely short acceleration path. This new device employs a pulsed plasma as the accelerative medium for the molten droplets. This pulsed plasma is capable of accelerating the droplets from the tips of the wires up to high velocities and atomizing them to very fine size. This results in a fine microstructure in the deposit. Recent experiments using a Control-Vision system measured velocities for aluminum droplets in the range of 950-1500 m/s and stainless steel droplets in the range of 850 m/s and 925 m/s. These velocities are achieved with an acceleration distance of only 3.2 cm, thus making this process an ideal candidate for coating the interior of automotive cylinder bores and other areas where only a short acceleration region is available.

The quality and durability of coatings produced by virtually all thermal spray techniques could be improved by increasing the velocity with which coating particles impact the substrate. Additionally, better control of the chemical and thermal environment seen by the particles during flight is crucial to the quality of the coating. A high velocity thermal spray device is under development through a BMDO SBIR project which provides significantly higher impact velocity for accelerated particles than is currently available with existing thermal spray devices. This device utilizes a pulsed plasma as the accelerative medium for powders introduced into the barrel. Recent experiments using a Control-Vision diagnostic system showed that the device can accelerate stainless steel and WC-Co powders to velocities ranging from 1500 to 2200 m/s. These high velocities are accomplished without the use of combustible gases, and without the need of a vacuum chamber, while maintaining an inert atmosphere for the particles during acceleration. The high velocities corresponded well to modeling predictions, and these same models suggest that velocities as high as 3000 m/s or higher are possible.