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 of plasma sprayed molybdenum and zirconia droplets deposited on different substrate 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 heat transfer in the melt, solidified splat and substrate is employed to perform a numerical analysis. A parametric study is conducted to examine the effects 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 for solidification can be as small as that for spreading and the rate of solidification can greatly influence the flattening degree. A guideline for when the effect of wetting angle and surface tension on droplet deformation can be neglected is derived. A correlation for the relationship between the flattening degree and Reynolds number with the consideration of solidification is deduced, and a criterion for the effect of droplet solidification on impact dynamics to be negligible is given. The limitations of the assumption of isothermal substrate are also discussed. The numerical predictions agree statistically well with the experimental data.