The hyper-branched structure is characterized by no preferred growth direction while \(\langle 110\rangle\) dendrites have distinctly crystallographic morphologies but with arms oriented parallel to \(\langle 110\rangle\). Starting from normal \(\langle 100\rangle\) dendrites in Al-rich alloys, a transition to hyper-branched dendrites and further to \(\langle 110\rangle\) dendrites happens when the content of Zn is increased. 12 show that the dendrite growth direction in Al–Zn (zinc) alloys changes with an increase in the solute content. With well-controlled experiments and simulations, Haxhimali et al. Due to its importance, experimental and modelling techniques have been devised to estimate the anisotropy of \(\gamma\) in several systems 8, yet the atomistic origin of this anisotropy remains elusive 9, 10, 11. Pure metals of cubic symmetry will exhibit dendrite arms extending along the \(\langle 100\rangle\) directions so as to minimize the content of high energy (100) surfaces. Moreover, the anisotropy also determines the crystallographic growth direction of the dendrites. 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.Īccording to the generally accepted microscopic solvability theory 6, 7, dendritic growth velocity and tip radius are sensitively controlled by the (small) anisotropy in the solid–liquid interfacial free energy, \(\gamma\). 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. This connection arises directly from the tendency for pattern formation via dendritic growth 1, 2 owing to the solid dendrite arms wanting to grow parallel to crystallographic directions whose interfacial energy is highest. The interfacial free energy also determines the characteristic scale and morphology of the microstructure of the solid. In solidification, it is the intrinsic properties of the solid–liquid interface that determines the morphology of the selected product phase and the composition distribution. Among the myriad of ways that interfaces impact on properties, one of the most important is their use to control microstructures resulting from phase transitions. Though interfaces constitute a vanishingly small volume fraction of bulk materials, they play an essential role in determining bulk properties. 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. 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. We observe a dendrite growth direction which changes from \(\langle 100\rangle\) to \(\langle 110\rangle\) as Sm content increases. 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. Previous work posited a dendrite orientation transition via compositional additions. 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.
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