Marangoni Migration Research Articles

Viscous Marangoni migration of an inviscid bubble by surfactant spreading: an exactly solvable model

A model is formulated of a two-dimensional migrating, or swimming, inviscid bubble in a viscous fluid whose unsteady displacement is caused by the spreading over its surface of an initial distribution of insoluble surfactant. Assuming small capillary and Reynolds numbers, and a linear equation of state giving the surface tension as a function of surfactant concentration, the quasi-steady Stokes flow around the bubble is found analytically and explicit formulas are determined for the time-dependent bubble speed and its final overall displacement. At infinite surface Péclet number this is done using a complex version of the method of characteristics to solve a complex partial differential equation of Burgers type. For a finite non-zero surface Péclet number, the problem is shown to be linearizable by a complex variant of the classical Cole–Hopf transformation. The formulation allows general statements to be made on the bubble speed and its total net displacement in terms of the initial surfactant distribution. A weak finite-time singularity in the surface activity associated with an isolated clean point on the bubble surface is also identified and studied in detail.

The Numerical Simulation of Marangoni Problems Employing Multi-phase Parallel SPH Method

When facing microscale problems, the phenomenon of droplet movement caused by temperature gradients is usually attributed to the Marangoni effect. This study first constructed a multiphase smoothed particle fluid dynamics (SPH) system structure, integrating continuous surface force (CSF) model and multiphase model to explore the behavior of droplets under Marangoni effect. To further improve computational efficiency, this study also utilized the Open Multi Processing (OpenMP) parallel computing framework to perform parallel optimization on the SPH algorithm. Subsequently, the effectiveness of the constructed SPH framework in addressing thermal capillary phenomena was verified by simulating the Marangoni migration phenomenon of silicone oil droplets in fluorine solutions. In addition, this study also investigated the polymerization process of two droplets in microchannels under the Marangoni effect, and obtained the complete dynamic changes of droplets from motion to polymerization. During this period, we conducted a detailed analysis of the variation process of the velocity vector field, the spatial distribution of the temperature field, and the evolution characteristics of the surface tension gradient during the droplet movement process, thereby comprehensively revealing how the Marangoni effect drives the phenomenon of droplet movement and aggregation.

The Influences of Micro-Alloying Element Sn and Magnetic Field on the Microstructure Evolution of Al–Bi Immiscible Alloys

An investigation was conducted through directional solidification experiments to explore the impact of micro-alloying element Sn and a magnetic field on the solidification behavior of immiscible Al–Bi alloys, as well as the combined effect of Sn and the magnetic field. Experimental results show that the size distribution of the dispersed particles in the low-speed solidified Al–3.4 wt.%Bi alloy presents two peaks, while it only shows one peak when solidified at a relatively high speed. The addition of Sn not only can enhance the nucleation rate and the number density of the Bi-rich droplets in the sample, but also decrease the Marangoni migration velocity and the axial resultant velocity of minority phase droplets in front of the solidification interface. Thereby it promotes the formation of Al–Bi alloys with a well-dispersed microstructure. A static magnetic field with the strength of 0.2 T increases the number density of the dispersed particles and decreases the average size and the size distribution width of the dispersed particles. Under the effect of Sn addition and static magnetic field, the average radius of the dispersed particles R and the solidification velocity V0 satisfy R∝V0−1/3 when the alloy was solidified at a relatively low velocity, R and V0 satisfy R∝V0−1/2 when the alloy is solidified at a high velocity.

1G and microgravity tank self-pressurization: Research on cryogenic fluid thermal stratification

A correlation numerical model was constructed, and relevant experiments were simulated to investigate the influence of gravity level on the self-pressurization process of the cryogenic fluid of liquid nitrogen. The calculated results agreed well with the experimental data. On this basis, the influences of a normal gravity environment and a microgravity environment on the self-pressurization process of liquid nitrogen in the normal-temperature fluid Perfluoro-n-Pentane (PnP, or C5F12) tank of National Aeronautics and Space Administration (NASA) were analyzed. According to the calculation results, an explicit horizontal interface is formed between the gas and liquid phases in the tank during the 1G (G = 9.81 m/s2) self-pressurization process. The ullage pressure increases as time progresses, and obvious thermal stratification phenomena are observed in the ullage along the axial and radial directions. However, the thermal stratification of the liquid zone is not obvious. The ullage near the gas‒liquid interface shifts from counterclockwise movement to clockwise movement, while the liquid changes from clockwise movement to counterclockwise movement. In the process of microgravity self-pressurization, the gas‒liquid interface in the tank presents an irregular shape, and the ullage pressure increases continuously before 400 s and then tends to be stable. The axial thermal stratification of fluid in the tank tends to disappear as time progresses, but obvious radial thermal stratification is observed. The ullage in the tank moves up and down as a response to the Marangoni migration effect. The temperature of the liquid zone in the tank during 1G self-pressurization tends to be consistent more quickly than that during microgravity self-pressurization, and the average temperature is higher. However, the temperature reduction rate of the ullage in the tank during microgravity self-pressurization is higher than that during 1G self-pressurization. Numerical simulation results can provide references to further study the on-orbit pressure control technique of cryogenic liquid tanks.

Tailoring homogeneous immiscible alloy via magneto-Archimedes levitation

Processing of immiscible alloys with a homogeneous distribution of fine minor segregated phases is a great challenge. Al-10wt.%Bi immiscible alloys were solidified under the homogeneous and gradient high magnetic fields (HHMF and GHMF). X-ray computed tomography technique was applied to study the spatial features of the minor Bi-rich particles (MBPs). The results show that the MBPs displayed as centripetal and centrifugal distributions along the radial directions of the ingots solidified under the GHMF. The segregation of the minor Bi-rich droplets (MBDs) was dominated by both radial Marangoni migration and the vertical Stokes sedimentation under the HHMF. In the case of the GHMF, both the radial Marangoni migration and vertical Stokes sedimentation of the MBDs can be effectively stopped by the gradient forces. This work provides a novel path to design the novel alloys with homogeneous microstructures by utilizing the magneto-Archimedes levitation.

A comparative study of metastable phase separation for undercooled liquid Fe35Cu65 alloy under natural and forced cooling conditions

The influences of the cooling style on metastable phase separation (MPS) kinetics of undercooled liquid Fe35Cu65 alloy have been systematically investigated by glass fluxing technique and lattice-Boltzmann method. MPS was observed in the undercooling range of 13–285 K. With a rise in the undercooling, phase separation time increased linearly. Meanwhile, a microsegregation morphology, which appeared as Fe-rich globules near the sample surface and well-defined αFe dendrites far from the sample surface, transformed into the eccentric core-shell macrosegregation morphology composed of a floating Fe-rich core and a sinking Cu-rich shell. Under the forced cooling condition, the macrosegregation formation required a larger critical undercooling. In contrast with the naturally cooled sample, the phase separation time of forcedly cooled sample was much shorter, and both the eccentric level of the core-shell macrosegregation and the volume fraction of Fe-rich zone were smaller at the same undercooling. The MPS and microstructure evolution of liquid Fe35Cu65 alloy under the natural and forced cooling conditions were numerically simulated and experimentally confirmed. Theoretical analyses revealed that the fluid dynamics caused by the Stokes motion and Marangoni migration of Fe-rich globules were strongly dependent on the cooling style, the size and the position of Fe-rich globules during the MPS.

Microstructural evolution and magnetic property of a rapidly solidified ternary Fe37.5Cu37.5Sn25 peritectic-type alloy

The liquid Fe37.5Cu37.5Sn25 peritectic-type alloy was rapidly solidified by glass fluxing, drop tube, and melt spinning techniques. The solidification structures consisted of three phases, including the αFe solid solution and the Cu3Sn and Cu6Sn5 intermetallic compounds under different conditions. In this work, the bulk undercoding ΔT equals the liquidus temperature TL minus the nucleation temperature TN of the primary solid phase. During the bulk undercooling process, a maximum liquid undercooling of 272 K (0.18TL) was achieved. Metastable liquid phase separation was induced if the undercooling exceeded 177 K. Within a moderate undercooling range from 8 to 177 K, the solidified structures showed coarse dendrites, and the dendritic growth velocity increased to 41.5 mm/s following a power relation. As the drop tube technique provided a containerless state, a maximum surface cooling rate of 3.5 × 104 K/s was achieved. The alloy droplets displayed metastable liquid phase separation even at the largest droplet diameter of 944 μm. The cooling rate and thermal Marangoni migration were found to greatly influence the phase-separated patterns of the alloy droplets. Under the melt spinning condition, the microstructures of the Fe37.5Cu37.5Sn25 alloy ribbons were significantly refined and displayed soft magnetic characteristics. Furthermore, the experimental results demonstrated that the grain size of the αFe phase affected the coercivity of the alloy ribbons.

Effect of Sn addition on morphology evolution of secondary phase in hypomonotectic Cu-Pb-Sn alloy during solidification

In the present study, the Cu-24Pb-xSn (wt.%) alloys with Pb-rich secondary phase particles (SPPs) in different morphology were prepared by intermediate frequency induction heating technology. The experimental results show that the SPPs transform from network to rod-like morphology with Sn content increasing from 0 wt% to 6 wt%. The relevant function mechanism of Sn addition was revealed through synchrotron X-ray radiography and thermodynamic analysis. It is indicated from the thermodynamic calculation that Sn addition can weaken the demixing tendency in Cu-Pb system. This can also lead to intensity drop of the monotectic reaction which was characterized by differential scanning calorimetry (DSC). Simultaneously, a triple-phase-coexistence (TRPC) region is introduced with Sn addition during solidification, which contains a Cu-rich liquid (L1), a Pb-rich liquid (L2) and a solid α-Cu (S). Benefitted from the mobility of these two immiscible liquids, L2 tends to show regular rod-like morphology and finally transform to rod-like SPPs, which is similar to some immiscible alloys containing an immiscibility gap, such as Al-Pb, Al-Bi and Ti-Ag alloys. The width of TRPC region in the pseudobinary phase diagram of Cu-Pb-Sn alloy increases with increasing Sn content. This is attributed to the fact that increasing Sn content can lead to the drop of interfacial tension between L1 and L2. Simultaneously, the interfacial tension drop will decrease the Marangoni migration velocity of the SPPs, and the Marangoni migration serves as the main driven force of SPPs' collision and coagulation in this case. Therefore, Sn addition is helpful to obtain fine and dispersed SPPs in this case. This work possesses guiding significance to the composition design and production of relevant hypomonotectic alloy with homogeneous and refined microstructure.

Liquid phase separation and core–shell morphology of Al75Bi9Sn16 immiscible alloy

ABSTRACTIn this paper, the liquid phase separation (LPS) of liquid immiscible Al75Bi9Sn16 alloy was investigated with calorimetric, thermal analysis and resistivity methods. Based on the fact that the resistivity depends on the composition of two separated liquid phases, the interface area between two separated liquid phases and the volumetric fraction of Sn–Bi-rich liquid x, the LPS can be divided into three stages: nucleation in the range from 1028 to 984 K; diffuse growth and Brownian coagulation in the range from 984 to 925 K; Marangoni migration, Stokes aggregation and coalescence in the range from 925 to 866 K. In addition, the Sn–Bi-rich@Al-rich core–shell structure was formed in Al75Bi9Sn16 alloy, resulting from the Marangoni migration. Based on the results in this study, an efficient method was developed to investigate the thermodynamics and kinetics of LPS of immiscible alloys.

Novel insight into evolution mechanism of second liquid-liquid phase separation in metastable immiscible Cu-Fe alloy

The metastable immiscible Cu80Fe20 alloys with different diameters were systematically investigated under conventional solidification. Experimental results indicated that the primary and second liquid-liquid phase separation simultaneously occur during solidification. The average size of primary phase-separated Fe-rich spherulites and the interior morphological pattern of minority Cu-rich phase can be greatly influenced by cooling rate due to the dynamic coupling between thermodynamic and kinetic effects. Moreover, various morphological patterns of minority Cu-rich phase in Fe-rich spherulites were observed, which discloses the dynamic evolution process during self-driven second liquid-liquid phase separation. The Marangoni migration, coalescence and coagulation, and Ostwald ripening are the dynamic mechanisms mainly responsible for various morphological patterns of minority Cu-rich phase after phase separation. Such a clear experimental observation of dynamic microstructure evolution for minority Cu-rich phase provides a strong and visualized evidence for the asynchronous crystallization behavior of primary phase-separated Fe-rich spherulites. Phase field simulation was also performed to reveal the dynamic evolution of minority Cu-rich phase during liquid-liquid phase separation. Besides, the experimental Cu80Fe20 alloys exhibit soft ferromagnetic characteristics possessing relatively low coercivity and high saturated magnetization. This present study provides a new strategy to design immiscible alloy with anticipated microstructure possessing tailored properties and desired functionalities.

Liquid Phase Separation Mechanism of Cu‐40 wt.% Pb Hypermonotectic Alloys

Solidification microstructures of Cu‐40 wt.% Pb alloy were examined under different undercooling degrees. The liquid phase separation mechanism in the systems with stable miscibility gaps mainly involved Ostwald ripening, Brownian motion, Marangoni migration, and Stokes motion. Stokes had little influence on the liquid phase separation in the early phase and played a leading role in the later period. The liquid phase separation mechanism of Cu‐40 wt.% Pb hypermonotectic alloy was illustrated in detail.

Assessment of VOF Strategies for the Analysis of Marangoni Migration, Collisional Coagulation of Droplets and Thermal Wake Effects in Metal Alloys Under Microgravity Conditions

A possible approach for the investigation of a number of aspects related to the processing of immis- cible alloys, made possible by recent progress in both fields of moving boundary (VOF) methods and speed of computers, is discussed. It can capture in a single nu- merical treatment and without limiting assumptions both macroscopic information (i.e. the macrophysical prob- lem, heretofore treated in terms of population dynam- ics) and microscopic details (i.e. the microphysical prob- lem, heretofore treated within the framework of bound- ary integral methods and/or under the assumption of non- deformable drops). The role played by coalescence in changing the Marangoni migration velocity is discussed together with the possible influence of thermal wake ef- fects for small and large values of the Prandtl number. Some prototype preliminary (very heavy) simulations are used for a better representation of some still unexplored or overlooked aspects. keyword: Microgravity, Volume of Fluid method, Marangoni effects, Metal alloys.

Walls and domain shape effects on the thermal Marangoni migration of three-dimensional droplets

The thermocapillary motion of liquid droplets in fluid media depends on a variety of influential factors, including the not yet fully understood role played by the presence of the walls and other geometrical constraints. In order to address this specific question, in the present work, we rely on a rigorous mathematical and numerical framework (including an adaptive mesh strategy), which is key to perform physically consistent and computationally reliable simulations of such a problem given the different space scales it involves. Our final aim is the proper discernment of the triadic relationship established among viscous phenomena, thermal effects, and other specific behaviour due to the proximity of the droplet to a solid boundary. Different geometric configurations are considered (e.g., straight, converging, and diverging channels and droplets located near a single or adjacent walls), and distinct regimes are examined [including both (Ma, Re) → 0 and finite Ma flows]. The results show that for straight ...

Selective laser melting of W-Ni-Cu composite powder: Densification, microstructure evolution and nano-crystalline formation

As the typical refractory metal, the W-Ni-Cu alloy faces severe challenge in machining of complex shapes. To deal with the problem, we use selective laser melting (SLM) additive manufacturing to consolidate W-10%Ni-10%Cu composite powder. The effects of laser parameters on densification, microstructural evolution and nano-crystalline formation were studied. With the increase of laser energy density, the absolute density increases apparently and the surface unevenness is slightly alleviated. Except the typical W and Ni-Cu solid solution phases, interestingly, the amorphous W-Ni solid solution was detected in the SLM processed sample. The typical microstructure contains un-melted W region, W dendrite region with the melting of W and Ni-Cu region. The W solidification microstructure adjacent to the un-melt W presents cellular grain and then transforms into columnar dendrite, until it finally becomes equiaxed dendrite. A large number of W-based nanocrystals formed during the solidification process, which was caused by Marangoni migration that the Ni-Cu phase tends to break the liquid W into small ones, yielding the formation nano-crystalline. Better understanding of the corresponding metallurgical mechanisms will help pave the way towards newly refractory metal design for additive manufacturing application.

Numerical Simulation of Droplets Behavior of Cu-Pb Immiscible Alloys Solidifying under Magnetic Field.

A model has been presented for the coarsening of the dispersed phase of liquid-liquid two-phase mixtures in Cu-Pb alloys under the effect of a high magnetic field (HMF). The numerical results show that the evolution of size distribution is the result of several factors and the diffusional growth, the collision-coagulation of the Cu-rich droplets (gravity sedimentation and Marangoni migration), and melt flow also have obvious effects on the movement of droplets and coarsening process. The effect of the HMF in the coarsening process of Cu-Pb alloy is studied in this work both by simulation and experiment. The analysis shows that the HMF leads to a decrease in the melt flow velocity, and can also lead to a decrease in the moving velocity of Cu-rich droplets. The HMF significantly reduces the coarsening rate of droplets as compared by the distribution evolutions. Finally, it is shown that droplet collision and coagulation can be dramatically retarded by the HMF. The results of the simulation are compared with the experiments performed with immiscible Cu-Pb alloys, and the discrepancy between theory and experiment is discussed.

Influence of a Direct Current on the Solidification of Immiscible Alloys

Continuous solidification experiments were carried out with immiscible alloys under the effect of a direct current. The experimental results demonstrate that a direct current shows a significant effect on the migration of minority phase droplets (MPDs) in continuously solidified immiscible alloys. It can promote the formation of a well dispersed microstructure or a core/shell microstructure. A model describing the kinetics of the microstructure evolution in a continuously solidified immiscible alloy was developed. The microstructure formation in the alloys was calculated. The numerical results are in favorable agreement with the experimental ones. They demonstrate that a direct current may affect the microstructure development through changing the spatial motions of MPDs. The alloys show a well dispersed microstructure when they are solidified with such a direct current density that the direct current causing motion of the MPDs is almost equivalent to the radial component of the Marangoni migration velocity of the MPDs. The alloys show a core/shell microstructure when they are solidified with such a direct current density that the direct current causing motion of the MPDs dominates the migration of the MPDs along the radial direction of the sample. A wire or rod with well dispersed microstructure or a core/shell microstructure can be prepared by solidifying immiscible alloys under the effect of a direct current properly chosen.

Dynamic evolution process of multilayer core-shell microstructures within containerlessly solidifying Fe(50)Sn(50) immiscible alloy.

Multilayer core-shell structures are frequently formed in polymers and alloys when temperature and concentration fields are well symmetrical spatially. Here we report that two- to five-layer core-shell microstructures were the dominant structural morphology of a binary Fe(50)Sn(50) immiscible alloy solidified under the containerless and microgravity states within a drop tube. Three dimensional phase field simulation reveals that both the uniformly dispersive structure and the multilayer core-shells are the various metastable and transitional states of the liquid phase separation process. Only the two-layer core-shell is the most stable microstructure with the lowest chemical potential. Because of the suppression of Stokes motion, solutal Marangoni migration becomes important to drive the evolution of core-shell structures.

Migration and alignment of Fe-rich particles in Cu melt under high magnetic field

The interaction among particles in front of solid-liquid interface during solidification plays a role in determining the trajectories, distribution and sizes of particles, which eventually determines the properties of material. By using the interaction to control the migration of particles, impurity particles can be removed from the melt. A method of using an external high magnetic field to simulate the migration of Fe in Cu melt is proposed. Static high magnetic field (0.1 Tesla and 12 Tesla) and gradient high magnetic field (-92.1 T2/m) are subjected to the solid-liquid mushy zone of Cu-30 wt%Fe alloy. The case without high magnetic field is also investigated for comparison. Both macro- and microstructure of the samples are observed by optical microscope. The results indicate that primary Fe dendrites in Cu-Fe alloy are transformed into spherical Fe-rich particles after solidification in mushy zone, and high magnetic field is capable of changing the migration, distribution and arrangement of Fe-rich particles. In the absence of a static high magnetic field, Fe particles are distributed in Cu melt homogeneously. With increasing the magnetic flux density of imposed static high magnetic field, Fe-rich particles gradually migrate upwards. The migration direction is opposite to the direction of the gravity, and there are no Fe-rich particles kept on the bottom of the samples imposed by magnetic field. In the presence of negative high gradient magnetic field, however, the Fe-rich particles migrate downward and the direction is along the direction of the gravity. A model is built up to clarify the body force of Fe-rich particles and to analyze their movement while they are affected by high magnetic field. The results show that the migration behaviors of Fe-rich particles are related to the viscous dragging force, the interaction force between magnetic dipoles, and the magnetization force induced by gradient high magnetic field. The displacement of Fe particles is closely dependent on the body force. Through the analysis the experimental results are well explained. The diameters of Fe-rich particles are statically summarized under different high magnetic field conditions and in different zones. With increasing magnetic flux density of static high magnetic field, the aggregation of particles is increased. The magnetic field gradient, however, reduces the aggregation of particles. This might be as a result of the competitive coagulation between Stokes sedimentation and Marangoni migration in Cu melt. Microstructure of the samples indicates that Fe-rich particles tend to align along the direction of high magnetic field and the degree of alignment is likely to be related to external magnetic field strength, resistance force, effective time, and initial condition of particles, etc. As they are parallel to the direction of high magnetic field, the energy of the system is minimum, suggesting that the system is stable. The present study shed light on how to remove strong magnetic impurity from Cu melt.

Experimental investigation and numerical simulation on liquid phase separation of ternary Fe-Sn-Si/Ge monotectic alloy

The liquid phase separation of small Fe-Sn-Si/Ge alloy droplets under reduced-gravity condition is investigated experimentally by free fall technique and theoretically by lattice Boltzmann method. In the drop tube experiments, the Fe-Sn-Si/Ge monotectic alloys are heated by induction heating in an ultrahigh vacuum chamber and further overheated to 200 K above their liquid temperatures for a few seconds. Finally, the molten alloy melt is ejected out from the small orifice of a quartz tube by high pressure jetting gas of He and dispersed into numerous tiny droplets, which are rapidly solidified during free fall in a protecting He gas environment. These droplets benefit from the combined advantages of high undercooling, containerless state and rapid cooling, which can provide an efficient way to study the liquid phase separation of high-temperature alloys in microgravity. In order to efficiently reproduce the dynamic process of phase separation inside drop tube equipment, the effects of surface segregation and Marangoni convection are introduced into the interaction potential of different liquids within lattice Boltzmann theory. Based on this modified model, the dynamic mechanism of phase separation can be sufficiently analyzed and the phase separation patterns can be realistically simulated. Experimental results demonstrate that conspicuous liquid phase separations have taken place for both Fe-Sn-Si and Fe-Sn-Ge alloy droplets and the corresponding morphologies are mainly characterized by core-shell and dispersed structures. The phase separation process can be modulated by the third-element addition. As the Si element of Fe-Sn-Si alloy is replaced by the Ge element with the same fraction, the distribution order of Fe-rich and Sn-rich zones is reversed within core-shell structure. A core-shell structure composed of a Fe-rich core and a Sn-rich shell is frequently observed in Fe-Sn-Si alloy droplets whereas the Fe-Sn-Ge alloy droplets tend to form a core-shell structure consisting of a Sn-rich core and a Fe-rich shell. Theoretical calculations show that the droplet cooling rate is closely related to droplet size: a smaller alloy droplet has a higher cooling rate. The liquid L2(Sn) phase always nucleates preferentially and forms tiny globules prior to solid Fe phase. Stokes motion can be greatly weakened in this experiment and the Marangoni migration dominates the globule movement in the process of liquid phase separation. Furthermore, the intensity of Marangoni convection within Fe-Sn-Ge alloy droplets is significantly stronger than that inside Fe-Sn-Si alloy droplets. Numerical simulations reveal that the cooling rate, Marangoni convection and surface segregation play the important roles in determining the selection of core-shell configurations and the formation of dispersed structures. Ultrahigh cooling rate contributes to forming the dispersed structures. When the Marangoni convection proceeds more drastically than the surface segregation, the minor liquid phase with a smaller surface free energy migrates to droplet center and occupies the interior of droplet, otherwise most of the minor phases appear around the periphery of droplet.

Liquid-liquid phase separation of freely falling undercooled ternary Fe-Cu-Sn alloy.

The active modulation and control of the liquid phase separation for high-temperature metallic systems are still challenging the development of advanced immiscible alloys. Here we present an attempt to manipulate the dynamic process of liquid-liquid phase separation for ternary Fe47.5Cu47.5Sn5 alloy. It was firstly dispersed into numerous droplets with 66 ~ 810 μm diameters and then highly undercooled and rapidly solidified under the containerless microgravity condition inside drop tube. 3-D phase field simulation was performed to explore the kinetic evolution of liquid phase separation. Through regulating the combined effects of undercooling level, phase separation time and Marangoni migration, three types of separation patterns were yielded: monotectic cell, core shell and dispersive structures. The two-layer core-shell morphology proved to be the most stable separation configuration owing to its lowest chemical potential. Whereas the monotectic cell and dispersive microstructures were both thermodynamically metastable transition states because of their highly active energy. The Sn solute partition profiles of Fe-rich core and Cu-rich shell in core-shell structures varied only slightly with cooling rate.