Modeling And Characterization Of The Solidification Of Mono-Sized Sn-5wt.%Pb Droplets Produced By The Uniform Droplet Spray Process

Spray forming processes offer a short-cut route to the efficient production of parts with optimum microstructures and properties, as opposed to the more inefficient conventional ingot-metallurgy based materials processing and manufacturing processes.A calorimetric method suitable for determining the enthalpy of droplets in a uniform droplet spray was developed and used to determine the enthalpy of Sn-5wt.%Pb uniform droplets as a function of flight distance. The need for droplet collection in a calorimeter inevitably creates non-adiabatic conditions in such calorimeter. In the developed method, the heat loss from the calorimeter is accounted for so that the heat balance equation can be integrated for the actual enthalpy transfer from the droplets to the calorimeter fluid. And then we could obtain the droplet's temperature when it felled into the fluid. Alter the position of the calorimeter step by step and acquired T (temperature)-D (Distance) curve.A homogeneous nucleation model has been developed by Ando etc, to address the fast solidification of uniform droplets generated by UDS process. Then we considered that the nucleation progress must be a heterogeneous progress, since there were plenty of metal atoms should be oxidized when they flying in the atmosphere which contained oxygen. So we import the oxide rate to revise the model. Two methods were developed that permits computation of CCT diagrams for surface oxidation catalyzed heterogeneous nucleation of alloy droplets from a few experimental data. One is the physics method, which addresses the progress of droplet surface oxidation during continuous cooling in terms of oxide nucleation and growth kinetics. Avrami-corrected surface oxidation kinetics is adopted to account for the impingement of oxide islands growing on the droplet surface during continuous cooling. The method predicts droplet nucleation kinetics in relation to the oxidation potential in the atmosphere, droplet diameter, cooling schedule and four temperature-independent constants. CCT diagrams were computed for Sn-5wt%Pb droplets cooling in nitrogen atmospheres with various oxidation potentials using nucleation data and cooling simulation of traveling mono-size droplets. Calculated CCT diagrams show that droplet surface oxidation sharply increases the droplet nucleation temperature particularly at high cooling rates.Otherwise, we developed a chemical method to compute oxide rate, and...