Flow field and its effect on microstructure in cold crucible directional solidification of Nb containing TiAl alloy

A 3D finite element model was established to investigate the flow field in TiAl melt under different process parameters that include the position of the solidification interface, the meniscus height, the heating power and the current frequency. A square cold crucible with an inner cross section of 36 mm × 36 mm was employed to directionally solidify Ti–46Al–6Nb–B (at.%) ingots. The flow pattern in the melt is highly parameter-related. Generally, there are two flow swirls with opposite directions in the melt. The flow near the solidification interface can be minimized with an optimal meniscus height. The flow velocity is decreased with a decrease of heating power and an increase of current frequency. A weaker lateral flow near the solidification interface is beneficial for the continuous growth of columnar grains. The microsegregation of a directionally-solidified ingot can be reduced by controlling the flow in the melt, which is one of the advantages of cold crucible directional solidification.