Effect of cross-section-change induced advective flow on the primary dendrite array morphology of hypoeutectic Pb-Sb alloys during directional solidification

Abstract

The morphology and distribution of primary dendrites have been examined in Pb-2.2, 5.8 and 10.8 wt. pct. Sb alloy samples directionally solidified (DSed) in ampoules shaped like an hour-glass to examine the influence of cross-section change induced advective flow on the cellular/dendritic interface. This sample design increases the advective flow of the melt towards the array tips, as the liquid-solid interface enters the neck of the ampoule, and then decreases it as the interface exits the neck. The warm solute-rich melt flowing towards the growth front suppresses the extent of side-branching, decreases the primary dendrite spacing, and increases the primary dendrite trunk diameter as observed in the Pb-5.8 and 10.8 Sb alloys. The flow appears to suppress the formation of cells. A cellular interface growing in the Pb-2.2Sb alloy became planar as the solidification front entered the neck, becoming cellular again as it exited the neck.

A Review of Large-Scale Simulations of Microstructural Evolution during Alloy Solidification

“…Permeability will be discussed in more detail in a later section. In order to evaluate the arrays, ordering, and spacing of primary arms, especially in 3D directional growth, different methods have been employed historically such as minimum spacing tree [166], Fourier transformation [167], Voronoi decomposition [168], and many others [169][170][171][172]. Using a modified Voronoi decomposition technique, where the small sides are removed from the Voronoi cells, the primary arm array was evaluated by Takaki et al [173].…”