[Paper Review] Controlling solid-liquid interfacial energy anisotropy through the isotropic liquid

Lei Wang, Jeff Hoyt+3 more|arXiv (Cornell University)|Oct 12, 2018

Solidification and crystal growth phenomenaMaterials Science38 references3 citations

TL;DR

This study experimentally and computationally demonstrates that solute concentration in Al-Sm alloys controls solid-liquid interfacial energy anisotropy, inducing a dendrite growth direction transition from ⟨100⟩ to ⟨110⟩ with increasing samarium content. Molecular dynamics simulations confirm that the anisotropy parameters ε₁ and ε₂ shift within the (ε₁, −ε₂) space, providing direct evidence for composition-driven interfacial energy anisotropy variation in binary alloys.

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 <100> to <110> 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 conjecture in previous works. In addition, our results provide physical insight into the atomic structural origin of the concentration dependent anisotropy, and deepens our fundamental understanding of solid-liquid interfaces in binary alloys.

Motivation & Objective

• To experimentally investigate how solute concentration affects dendrite growth direction in Al-Sm alloys.
• To determine the atomic-scale origin of concentration-dependent interfacial energy anisotropy in solid-liquid interfaces.
• To validate the hypothesis that interfacial free energy anisotropy varies with composition, leading to dendrite orientation transitions.
• To provide a direct link between solute content, interfacial stiffness, and anisotropy parameters (ε₁, ε₂) in a binary alloy system.
• To deepen fundamental understanding of solid-liquid interface behavior in metallic systems through combined experiment and simulation.

Proposed method

• Used molecular dynamics (MD) simulations to compute interfacial free energy anisotropy in Al-Sm systems across varying Sm concentrations (0–15 at.%).
• Applied the Capillary Fluctuation Method (CFM) to extract interface stiffness from Fourier amplitudes of interface height fluctuations in (100) and (110) oriented crystal-melt interfaces.
• Calculated anisotropy parameters ε₁ and ε₂ using the stiffness values from (100) and (110) interfaces via the relation γ(n)/γ₀ = 1 + ε₁(Q − 3/5) + ε₂(3Q + 66S − 17/7), where Q and S are cubic harmonics.
• Performed semi-grand canonical Monte Carlo simulations to determine chemical potential differences between liquid and FCC solid phases at 800–900 K, enabling Gibbs free energy construction.
• Used local order parameter φ = (1/12)Σ|rᵢ − r_fcc|² to locate and quantify interface position and width via hyperbolic tangent fitting.
• Collected 6,000 snapshots over 6 ns from 4 independent replicas per system to ensure statistical reliability in stiffness and anisotropy estimation.

Experimental results

Research questions

• RQ1 How does increasing samarium concentration in Al-Sm alloys affect the dendrite growth direction?
• RQ2 What is the role of interfacial energy anisotropy in driving the observed dendrite orientation transition from ⟨100⟩ to ⟨110⟩?
• RQ3 Can molecular dynamics simulations quantitatively reproduce the composition-dependent variation in interfacial free energy anisotropy parameters ε₁ and ε₂?
• RQ4 What is the atomic-scale structural origin of the changing anisotropy in solid-liquid interfaces of Al-Sm alloys?
• RQ5 Does the (ε₁, −ε₂) space trajectory for Al-Sm align with the predicted regimes for ⟨100⟩, hyper-branched, or ⟨110⟩ dendritic growth?

Key findings

• Dendrite growth direction in Al-Sm alloys transitions from ⟨100⟩ to ⟨110⟩ as samarium concentration increases from 0 to 15 at.%
• The interfacial free energy anisotropy parameters ε₁ and ε₂ vary with solute concentration, shifting the system’s position in the (ε₁, −ε₂) parameter space from the ⟨100⟩-dominated to the ⟨110⟩-dominated regime.
• Molecular dynamics simulations confirm that the (100) and (110) interface stiffnesses vary systematically with Sm content, enabling quantitative extraction of ε₁ and ε₂.
• The observed dendrite orientation transition is directly correlated with the computed variation in interfacial energy anisotropy, providing definitive experimental and simulation-based confirmation of prior conjectures.
• The study reveals that interfacial ordering in the liquid near the solid-liquid interface plays a key role in modulating anisotropy, linking atomic-scale structure to macroscopic growth morphology.
• The results demonstrate that solute concentration can be used as a tunable parameter to control interfacial energy anisotropy, offering a new route to engineer microstructure in metallic alloys.