Phase field simulation of dendrite growth in gas atomized binary Al-Ni droplets

Catalytic powders with fine microstructures can be produced from a rapidly solidified gas atomized Al-Ni alloy.The solidification microstructure of the droplets is closely linked with heat flow conditions.Thus,the heat transfer conditions between the gas and droplet are essential to microstructural evolution.In this study,a phase field model for simulating single and multiple dendrite growth in a binary Al-Ni alloy was constructed and the microstructural evolutions occurring during a gas atomization process were evaluated.Temporal variations in the heat transfer coefficient and the boundary heat flux were taken into account.The results revealed that the heat transfer coefficient of the atomized droplet in flight is correlated with the droplet size and the relative velocity between the droplet and the atomizing gas.During the simulation,the competition between boundary heat flux extraction and latent heat release from phase transition causes a recalescence process in thermal history,thereby affecting the gradient temperature distribution and,consequently,the dendrite morphology.Dendrite growth under the effects of the heat transfer coefficient is restrained continuously because of the decreasing amount of extraction.The computational results confirmed the fine homogeneous microstructure and low microsegregation levels of gas atomized powders.