Characterization via image analysis of cross-over trajectories and inhomogeneity in twin wire arc spraying

By using a computer image analysis method, the microstructure of deposits arc sprayed with steel and copper wires as anode and cathode, respectively, were investigated and it was demonstrated that there exists a cross-over of the particle trajectories in the plume. Along the cross-section of the deposit, flattened particles from the anode and cathode wires were distributed in an asymmetric way about the centreline of the plume and varied gradually. For the deposits sprayed by an open nozzle system and a closed nozzle system with converging orifice, the locations of the maximum particle density of the anode and cathode materials did not coincide with each other and were not located at the centreline of the plume. However, for the deposit sprayed with a closed nozzle system and a converging–diverging orifice, such phenomenon was not obvious. By quantitative evaluation of the lamella structure of the deposits, it was found that the lamella thickness distribution followed a similar rule with that of the material content distribution. The above results indicate that in the twin wire arc spray process asymmetry in droplet formation and atomization results in remarkable inhomogeneity in coating microstructure.