Modeling layer-by-layer laser melting and solidification of binary alloy powder bed

A model for simulating layer-by-layer melting and solidification of a binary alloy powder bed due to a moving laser source is presented in this paper. The model uses a modified enthalpy-porosity approach to capture simultaneous melting and solidification of a powder bed. The effects of surface tension driven Marangoni convection and thermal and solutal buoyancy driven convection are incorporated in the model. Multiple layer formation is modeled by shifting the domain in the vertical direction to include the new layer. Simulations are performed for Al-Cu alloy to see the effect of different process parameters on the melt pool evolution, solute transport and segregation, and thermal transport with the primary focus on quantifying the nonhomogeneity in the final species distribution. Fixed melt pool results show that the effect of Marangoni convection is dominant resulting in considerably increased segregation in the solidified region. Simulation of layer-by-layer melting and solidification of the entire domain show that the solidified region can be divided into three zones based on solute distribution—initial low concentration zone, middle zone with slightly higher concentration, and the final zone with very high concentration. Subsequently, parametric studies are done that show that the nonuniformity in solute distribution can be reduced by reducing the laser power, increasing the laser spot radius, increasing the initial solute concentration, or decreasing the layer thickness.