Abstract
Although the anisotropy of the solid-liquid interfacial free energy for most alloy systems is very small, it plays a crucial role in the growth rate, morphology and crystallographic growth direction of dendrites. Previous work posited a dendrite orientation transition via compositional additions. In this work we examine experimentally the change in dendrite growth behaviour in the Al-Sm (Samarium) system as a function of solute concentration and study its interfacial properties using molecular dynamics simulations. We observe a dendrite growth direction which changes from langle 100rangle to langle 110rangle as Sm content increases. The observed change in dendrite orientation is consistent with the simulation results for the variation of the interfacial free energy anisotropy and thus provides definitive confirmation of a conjecture in previous works. In addition, our results provide physical insight into the atomic structural origin of the concentration dependent anisotropy, and deepen our fundamental understanding of solid-liquid interfaces in binary alloys.
Highlights
The anisotropy of the solid-liquid interfacial free energy for most alloy systems is very small, it plays a crucial role in the growth rate, morphology and crystallographic growth direction of dendrites
The authors showed that the observed dendrite orientation transition (DOT) could be explained by assuming that the solid–liquid anisotropy changes in some fashion with Zn concentration
It is difficult to assess whether the same structure observed in Fig. 5 is present in the Al–Zn system studied by Haxhimali et al, but it is worth noting that in Al–Zn the equilibrium crystal structure of Zn is HCP and not FCC
Summary
The anisotropy of the solid-liquid interfacial free energy for most alloy systems is very small, it plays a crucial role in the growth rate, morphology and crystallographic growth direction of dendrites. The practical significance of such dendritic growth and its consequences for the properties of bulk products are broad, from the strength of additively manufactured parts[3] to the performance of metal-ion batteries[4] The significance of this has driven an enormous body of work in the past 10–15 years aimed at identifying the key structural parameters that correlate to the properties of interfaces at the atomistic scale[5]. Compiling existing estimates of ε1 and ε2 for a variety of pure cubic metals, Haxhimali et al.[12] found that most lie inside the h100i region or near the h100i/hyper-branched boundary This is consistent with the dominance of h100i dendrites observed experimentally. It must be stressed that there is no direct evidence why such an anisotropy variation exists in
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