Dendritic to Globular Morphology Transition in Ternary Alloy Solidification

The evolution of solidification microstructures in ternary metallic alloys is investigated by adaptive finite element simulations of a general multicomponent phase-field model. A morphological transition from dendritic to globular growth is found by varying the alloy composition at a fixed undercooling. The dependence of the growth velocity and of the impurity segregation in the solid phase on the composition is analyzed and indicates a smooth type of transition between the dendritic and globular growth structures.

Figure 1

Transition from dendritic to globular morphology for different initial melt compositions at a constant initial undercooling of 20 K. Shaded regions correspond to the solid phase, i.e., $\varphi \ge 0.5$, and solid lines represent the isolines of average concentration of Ni in solid. The values for the tip velocities $V$ and for the area estimations $\delta$ are stated in each image.

Figure 2

Simulated area $S$ covered by the crystal in relation to a normalized triangular area $S_0$ for different melt compositions. The $\delta =0$ line marks the transition from dendritic to globular growth morphologies.