| The wire arc spray process, one of several thermal spray processes, allows for materials application onto surfaces. Historically this process received significant attention from the industry due to its simplicity of operation and low capital and running costs. Many of the modifications and improvements to this system came through trial and error experiments. Studies in the last decade into the wire arc process added much needed fundamental knowledge, however, a number of questions were left unanswered. The success of thermal spray systems is measured by the quality of the coating it produces. In the wire arc process, the quality of the coating depends on the speed, size and temperature of the particles as they impact the surface to be coated. The goal of this study is to understand the mechanisms of formation of the particles in the wire arc spraying process. This is done by investigating the wire melting, primary and secondary atomization stages. This also requires an understanding of the atomizing gas jet interactions with the wires and the arc disturbing its flow path and the subsequent effect on the particle formation and trajectories. The primary breakup mechanisms of the metal from the electrodes have been identified and the length and time scales of the liquid metal structures formed during these breakup mechanisms have also been quantified. The arc voltage and the sound signal fluctuations are an indication of metal detachment at high current settings. A strong correlation has been shown to exist between the primary breakup mechanisms and the final particle sizes. |
