Numerical simulation of fluid dynamic behavior of melting, mixing, vaporization and solidification for process optimization in in-situ alloying additive manufacturing

Abstract

Metal additive manufacturing (AM) is a promising digital manufacturing technology that can produce parts of complicated shapes. Fluid flow dynamics in melting and solidification determines the final shape accuracy and mechanical properties. Here, detailed numerical simulation is used for in-situ alloying to elucidate the processes of heating, melting, mixing, vaporization and solidification. The solidification process by the phase field method is coupled with the fluid flow dynamics. The laser heat input melts the powders of each element and a melt pool is formed. Here, entrainment and stirring of each element can enhance mixing in the melt pool, but complete mixing is not achieved in a single track. Grain growth is mostly governed by the thermal gradient and columnar grain growth is dominantly observed. The inhomogeneity of the chemical species induces a difference in the timing of grain growth, which may lead to collision of nearby growing grains. The second track melting induces remelting and further mixing occurs due to the stirring effect of the keyhole. It is suggested that controlling the keyhole dynamics by the heat input can control the species mixing and the grain growth. Optimization of such processes is our next future issue to be pursued.