Melt convection and macrosegregation in the vacuum arc remelted Ti2AlNb ingot: Numerical methods and experimental verification

Abstract

Vacuum arc remelting (VAR) is an ultra-high temperature and opaque process. It is difficult to conduct experimental research on the melt flow behavior and the formation of macrosegregation in this process. This work develops a two-dimensional Eulerian three-phase model to predict the solidification structure and macrosegregation of industrial Ti 2 AlNb ingots under complex multi-physics mechanism. The model is also used to study the influence of stirring magnetic field on the melt flow behaviors and macrosegregation of VAR ingots. The results show that Al content of the columnar zone increases gradually from the outside to the inside due to the flow behavior of the melt and the sedimentation of equiaxed grains. External magnetic field applied to stabilize the arc also makes significant effects on the melt convection and macrosegregation. Stirring Lorentz force induced by the external magnetic field drives the melt flow to rotate as a centrifugal force in the top, while drives the melt to flow downward along the metal pool and reduces the influence of the self-induced Lorentz force in the bottom. Superimposing the proper stirring magnetic field on the self-induced magnetic field can strengthen the solute mixing in the molten pool and improve the overall macrosegregation degree of the ingot. Increasing the stirring magnetic field can improve negative segregation in the center of the ingot but intensify the positive segregation in the periphery of the ingot.