Phase-field modeling of the dendrite orientation transition in Al-Zn alloys

Abstract

With a few exceptions, phase-field simulations of dendritic growth in cubic materials have been modeled using simple expressions for the interfacial energy anisotropy and with strong anisotropy. However, recent experimental results show that the Dendrite Orientation Transition (DOT) observed in Al-Zn alloys by Gonzales and Rappaz [Met. Mat. Trans. A37 (2006) 2797] occurs at weak anisotropy, and modeling these results requires at least two anisotropy parameters. In the present work, we solve the corresponding phase-field model on an adaptive grid, after measuring and compensating for the grid anisotropy. A systematic scan of equiaxed growth simulations was performed in the range of the anisotropy parameter space where the transition is expected. We find separate domains of existence of 100 and 110 dendrites, similar to those previously reported by Haxhimali et al. [Nat. Mat. 5 (2006) 660] for pure materials. In the so-called hyperbranched regime, lying between the 100 and 110 regions, we observe a competition between 100 and 110 growth directions, but no seaweed structures. Directional solidification simulations showed the stabilizing effect of the thermal gradient on the twofold splitting of 110 dendrites, and the importance of the choice of anisotropy parameters. We also found a strong dependence between the orientation of the crystal axes with respect to the thermal gradient and the actual growth direction. Finally, 3-dimensional seaweed microstructures were modeled for the first time, demonstrating that this pattern is a result of not only the values of anisotropy parameters, but also a consequence of directional solidification.

Influence of Cr on the nucleation of primary Al and formation of twinned dendrites in Al–Zn–Cr alloys: Can icosahedral solid clusters play a role?

“…This specific composition was selected because it has been shown to be the upper limit for which h1 0 0i dendrites are observed. Above this composition, the system exhibits a dendrite orientation transition (DOT), i.e., a gradual transition from h1 0 0i to h1 1 0i, which has been interpreted as a modification of the solid-liquid interfacial energy anisotropy [10,11,19]. In DS Al-20 wt.% Zn, we already found that minute additions of Cr (typically 200 to 1000 ppm) drastically modify the dendrite growth direction from h1 0 0i to h1 1 0i, but the reason in this case is less clear [20].…”

X-ray tomographic microscopy analysis of the dendrite orientation transition in Al-Zn

“…However, new findings show that the observed macroscopic texture did not necessarily correspond to the actual growth direction. The growth seems to operate by an alternating growth direction mechanism and could be linked to the competition between 100 and 110 characters, which was simulated using phase field under equiaxed growth conditions [4,14].…”

Phase-field Modeling and Simulations of Dendrite Growth

“…Therefore, various generalization schemes for high anisotropy have been developed. [103][104][105][106][107] A cusp interface energy model 108,109) has also been used to treat the facet and a high-anisotropy kinetic coefficient 110,111) has been modeled. Recently, dendrite growth simulations have been performed both in the 2D [112][113][114] and 3D 115,116) spaces for materials with the hexagonal close-packed structure, such as Mg alloys, which are the lightest metallic materials, and therefore, very important as future industrial materials.…”