Modelling the spreading behaviour of plasma-sprayed nickel droplets under different impact conditions

Abstract

Droplet spreading behaviour is critical in influencing the spreading diameters, material splashing and interfacial bonding conditions with the substrate during plasma spraying. Numerical simulations were performed to understand the effects of droplet impact temperatures, velocities and contact angle on spreading dynamics during the deposition of plasma-sprayed nickel splats. It was found that increasing droplet superheat (droplet temperature of 3000 K) was beneficial for increasing the degree of substrate melting and the droplet spreading diameters due to constrained solidification. However, solidification occurring at the droplet expanding front pinned the liquid–solid contact line and induced finger splashing for the case of 2800 K droplet temperature. The solidified layer disturbed droplet spreading and induced material jetting at the early spreading stage under the circumstance of high droplet impact velocities. A new simplified equation relating the maximum spreading ratios and Reynolds number was proposed. The effect of contact angle influenced droplet spreading under the condition of a large interfacial thermal contact resistance.