Effect of gas velocity and particle velocity on coating adhesion in wire arc spraying

In wire are spraying, atomizing gas velocity and particle velocity are important factors influencing coating quality. A nozzle with secondary gas injection has been developed to increase the gas velocity and to improve coating quality. In this study, wire are spraying of stainless steel on aluminum substrates has been investigated with the objective of establishing correlations between atomizing gas velocities, particle velocities, particle sizes and coating bond strength. Cold gas velocity is measured with a Pitot tube. Particle velocities are determined from high speed images of particle streaks taken with a Kodak high speed vision system and evaluated using image analysis. Bond strength is measured with pull-off tensile test. Secondary gas atomization clearly leads to improved adhesion due to additional metallurgical bonding between the coating and the substrate achieved through higher particle temperatures at the moment of impact.