Role of solidification, substrate temperature and Reynolds number on droplet spreading in thermal spray deposition: Measurements and modeling

Numerical analysis and experimental measurements of the flattening degree o f plasma sprayed molybdenum and zirconia droplets deposited on different su bstrate materials are presented. Investigation is focused on the influence of rate of solidification and wetting angle on droplet spreading. Madejski- Zhang model with one-dimensional treatment of solidification as well as hea t transfer in the melt, solidified splat and substrate is employed to perfo rm a numerical analysis. A parametric study is conducted to examine the eff ects of droplet size, impact velocity, superheating of droplets, substrate temperature, thermal contact resistance, and wetting angle on spreading of the splat and its flattening degree. Numerical results show that the time f or solidification can be as small as that for spreading and the rate of sol idification can greatly influence the flattening degree. A guideline for wh en the effect of wetting angle and surface tension on droplet deformation c an be neglected is derived. A correlation for the relationship between the flattening degree and Reynolds number with the consideration of solidificat ion is deduced, and a criterion for the effect of droplet solidification on impact dynamics to be negligible is given. The limitations of the assumpti on of isothermal substrate are also discussed The numerical predictions agr ee statistically well with the experimental data.