Phenomena during wire arc spray applications

The wire arc spray system is a widely used coating application tool offering high deposition rates at comparably low operational cost. An arc is ignited between two wire electrodes, which are constantly fed to compensate for the molten droplets detached from the tips by a strong perpendicular gas flow. Even though it is a commercially highly successful procedure, the investigations that have been reported on this method are still limited due to the highly complicated interactions between strong gas flows, changing electrode structures and reactive process gases. This paper aims at demonstrating some recent investigations into this technology to help understand the fundamental mechanisms as well as offering new diagnostic, which may be used to control the process to obtain higher quality and a better reproducibility. High-speed imaging shows a constant motion of the arc between the electrodes in the direction of the gas flow with regular re-ignition at the narrowest distance between the two wire tips. Droplet detachments vary depending their origin from the anodic and cathodic electrode due to the differences in arc attachment and energy input leading to a bimodal primary particle distribution, which has been modelled in good agreement with experimental results.