Rapid Solidification And Cooling Behavior Prediction Of Sn-Pb Alloy Droplet Produced By Uniform Droplet Spray

The uniform droplet spray (UDS) is a new technic of magneticpowder production which has the ability to produce mono-sized dropletsby controlling the breakup of a laminar jet with an externally appliedperturbation. Rapid solidification in the spray forming process results indesired deposit microstructures and mechanical properties. Study themicrostructure of the rapid solidification can provide scientific predictionand direction on the industrial production of alloy droplet. Study the continuous-cooling-transformation(CCT) diagram of thealloy droplet during its flighting can predicate the nucleation temperatureof the alloy droplet in theory. Control the cooling rate we can get thedesired microstructure of deposit. This paper revised the previous CCTcurves of the Sn-5wt.%Pb alloy droplet based on the heterogeneousnucleation theory. First revised the droplet oxidation fraction during its flight down withthe chemical reaction kinetics and transition state theory. After that wedeveloped a new physical model and with it we computed the oxidationfraction. Compute the CCT curves of Sn-5wt.%Pb alloy droplet. Based on thesurface oxidation nucleation theory we computed the CCT curves of 185μm and 155 μm droplet which solidified in nitrogen gas with 35 ppmoxygen and 166 ppm oxygen. We developed the internal nucleationtheory based on the surface oxidation nucleation theory and computed theCCT curves of 185 μm and 155 μm droplet which solidified in thenitrogen gas with 2% hydrogen. Because of the droplet produced by theindustrial is in gas atomization spray, we predicated the CCT curve of thegas atomized spray by changing the cooling schedule.As the chemical reaction kinetics theory is in the equilibrium statewhile the droplet produced by the UDS is in the non-equilibrium state, sowe put forward the physical model to compute the oxidation fraction. Foreliminate the overlap of the oxide, we revised the physical model further.Based on the physical model we can compute the CCT curve of the alloydroplet which solidified in nitrogen gas with 35 ppm oxygen.So far the chemical reaction kinetics method is consistent with thephysical method in computing the CCT curves of Sn-5wt.%Pb alloydroplet.