A numerical model for a hypoeutectic alloy droplet deposition with non-equilibrium solidification

A numerical model is developed to study the splat morphology and solidification characteristics of a molten hypoeutectic alloy droplet impinging and solidifying on a substrate. The study finds application in optimization and improvement of metal additive manufacturing processes such as solder jetting, microcasting, sputtering and 3D printing. The major mathematical and numerical challenges include solution of multiphase flow governing equations, interface tracking and modeling the non-equilibrium (rapid) solidification on a macroscopic domain. The free surface is tracked using a volume of fluid method with a piecewise linear interface construction while the mushy phase is modelled as a pseudo porous medium. An enthalpy formulation of the energy equation is coupled with the solute transport equation and the system is solved simultaneously for the temperature and concentration profiles until the eutectic point is reached; beyond which a special treatment is employed till complete solidification. Segregation models (with back diffusion) and eutectic phase diagram are incorporated in the solution procedure. The splat morphology, concentration profiles and microstructural properties are closely examined with emphasis on the convective effects and eutectic formation.