Non-equilibrium solidification of undercooled droplets during atomization process

Thermal history of droplets associated with gas atomization of melt has bee n investigated. A mathematical model, based on classical theory of heteroge neous nucleation and volume separation of nucleants among droplets size dis tribution, is described to predict undercooling of droplets. Newtonian heat now condition coupled with velocity dependent heat transfer coefficient is used to obtain cooling rate before and after nucleation of droplets. The r esults indicate that temperature profile of droplets in the spray during re calescence, segregated and eutectic solidification regimes is dependent on their size and related undercooling. The interface temperature during solid ification of undercooled droplets rapidly approaches the liquidus temperatu re of the alloy with a subsequent decrease in solid-liquid interface veloci ty. A comparison in cooling rates of atomized powder particles estimated fr om secondary dendrite arm spacing measurements are observed to be closer to those predicted from the model during segregated solidification regime of large size droplets.