Phase-field Modeling of Cellular and Dendritic Microstructure Formation during Directional Solidification of Binary Alloys under Diffusive Growth Conditions: Dynamical Selection of the Primary Spacing

International audienceWe have carried out three-dimensional phase-field simulations to model unique experimental observations of cellular and dendritic array structures formed under diffusive growth conditions aboard the International Space Station. We investigated two effects on the dynamical selection of the array spacing. The first is a recently characterized drift of isotherms inherent to the directional solidification set-up. Simulations show that this drift leads to a substantial increase of the dynamically selected spacing, thereby improving the quantitative agreement between simulated and observed spacings. Secondly, we investigated the effect of a finite misorientation between the principal crystal axes and the temperature gradient axis. Simulations show that this misorientation induces a slow spatiotemporal evolution of the array spacing towards a uniform spacing. This spacing is close to the upper limit of the stable range of spacings governed by tertiary branching and is larger than the spacing selected by the transient recoil of the interface