Immiscible Alloy Solidification Dynamics

Immiscible alloys are characterised by a liquid–liquid phase separation during cooling, often associated with a monotectic reaction in which a single liquid transforms into a primary solid plus a secondary liquid of differing composition. The dynamics of this process involve undercooling below the liquidus, rapid nucleation of dispersed droplets, and complex hydrodynamic interactions such as Marangoni convection and Stokes sedimentation. These combined effects govern the evolution of microstructures—including core–shell morphologies, monotectic cells and fine dispersions—by dictating droplet nucleation, growth, migration and coalescence. Control of cooling rate, composition and external fields (magnetic, acoustic or reduced gravity) enables tuning of phase distribution and minimisation of macrosegregation. Advances in simulation and in situ experimentation have deepened understanding of kinetic pathways and thermodynamic driving forces. Practical applications span lightweight sliding bearings, electronic packaging materials and porous scaffolds, where tailored microstructures deliver optimised mechanical, thermal and tribological performance.

Research from Nature Portfolio

Detailed investigation of a ternary Fe–Cu–Sn system under containerless free fall revealed the interplay between undercooling, phase separation time and Marangoni migration. Phase-field simulations, coupled with rapid solidification in microgravity, identified three distinct separation patterns—monotectic cells, core–shell and dispersive structures—and highlighted the core–shell morphology as the most stable configuration by virtue of its minimised chemical potential. Composition profiles across Fe-rich cores and Cu-rich shells were shown to vary little with cooling rate, evidencing robust partitioning characteristics.

The application of three orthogonal ultrasounds during the liquid-liquid separation of an Al–Sn–Cu alloy demonstrated an effective strategy for suppressing macrosegregation and droplet coalescence. Enhanced cavitation generated strong shockwaves that fragmented and uniformly suspended Sn-rich droplets within the Al-rich melt, producing a homogenous bulk composite. Numerical modelling confirmed that acoustic field geometry and sound pressure levels critically influence droplet stability and distribution.

Immiscible Alloy Solidification Dynamics publication trend

The graph below shows the total number of articles in immiscible alloy solidification dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

Monotectic reaction: A transformation in which one liquid phase solidifies into a solid plus a second liquid of distinct composition.

Liquid–liquid phase separation: The spontaneous demixing of a homogeneous melt into two immiscible liquid phases prior to solidification.

Undercooling: The temperature drop below the equilibrium liquidus required to initiate nucleation of a new phase.

Marangoni convection: Fluid flow driven by gradients in surface tension, often arising from temperature or composition differences.

Macrosegregation: Large-scale chemical inhomogeneity resulting from differential movement or settling of phases during solidification.

Core–shell structure: A morphology in which one phase encapsulates a core of the complementary composition, stabilised by interfacial energy minimisation.

References

1. Liquid-liquid phase separation of freely falling undercooled ternary Fe-Cu-Sn alloy. Scientific Reports (2015).
2. Three orthogonal ultrasounds fabricate uniform ternary Al-Sn-Cu immiscible alloy. Scientific Reports (2016).
3. In-situ composite microstructure formation of immiscible alloy solidified in space. National Science Review (2022).
4. Solidification of Immiscible Alloys under High Magnetic Field: A Review. Metals (2021).
5. Liquid-liquid phase separation and solidification behavior of Al55Bi36Cu9 monotectic alloy with different cooling rates. Results in Physics (2018).