Liquid–liquid Structure Transition Research Articles

The liquid-liquid structure change in eutectic Ga-Sn alloy

• The liquid-liquid structure transition did occur around the liquidus temperature. • Another liquid-liquid structure transition did occur in the range from 1073-1273 K. • Below and above the liquidus temperature, the liquid exhibits differences in viscosity, coordination numbers, correlation radius of cluster. The effect of temperature on dynamic viscosity and atomistic structure in liquid eutectic Ga-Sn alloy have been investigated by using a torsional oscillating viscometer, an X-ray diffractometer and the ab initio molecular dynamics simulation. The results indicated that the liquid-liquid structure transitions did occur around the liquidus temperature and in the range from 1073-1273 K. Below and above these temperatures the liquid exhibits differences in viscosity, coordination numbers, correlation radius of cluster, which are reflected from structural changes of structural disorder and local atomic packing. This work will trigger a further study on the liquid-to-liquid crossover in the liquid-solid transition.

Liquid state dependent solidification of a Co-B eutectic alloy under a high magnetic field

• Solidification behaviors in Co-B alloy dependent on the liquid state are studied. • The undercooling and recalescence extent are enlarged after experiencing LLST. • The wear resistance are significantly enhanced after experiencing LLST. • The concept of magentic-induced LLST is put forward firstly in Co-B alloys. The structure transition inside the Co-81.5at.%B alloy liquid has been studied by an in-situ magnetization measurement. A crossover was observed on the 1/ M - T curve during the overheating process, indicating that a liquid-liquid structure transition (LLST) took place in the melt. Based on this information, the effects of LLST on the solidification behavior, microstructure and tribology property were investigated experimentally. The sample solidified with the LLST exhibits significantly different solidification behaviors, i.e., the nucleation undercooling and the recalescence extent are conspicuously enlarged, and the solidification time is shortened. As a result, the microstructure is effectively refined and homogenized, and the hardness and wear resistance are significantly enhanced. The present work might be helpful for not only theoretically understanding the influence of LLST on the solidification behavior but also providing an alternative approach to tailor the microstructure and properties.

Surface Tension and Kinematic Viscosity of Multicomponent FeCuNbSiB Melt

This work investigated the surface tension and kinematic viscosity of the multicomponent Fe73.5Cu1Nb3Si13.5B9 melt. A relationship was found between surface tension and kinematic viscosity, which manifests itself in a synchronous change in these quantities at temperatures of 1600 and 1780 K. In the temperature range 1600–1780 K, there is a sharp increase in surface tension upon heating and the same decrease upon cooling. The increase in surface tension during heating was explained by the appearance of a large number of free Nb atoms as a result of the dissolution of the residual crystalline phase in the mushy zone, and their diffusion to the melt surface. The drop in the surface tension on cooling below 1780 K is associated with the liquid–liquid structure transition (LLST), which stimulates the outflow of Nb atoms from the surface in order to form new stable clusters. The LLST manifests itself in a change in the activation energy of a viscous flow, which is higher in the high-temperature region and corresponds to the motion of larger clusters with a length scale of about 1 nm.

Thermodynamic stability of microheterogenic states in Fe – Mn – C melts

Possibility of existence of microheterogeneous states in Fe – Mn – C melts was analyzed carried out according to the concepts of chemical thermodynamics. Microheterogeneous state of a chemically inhomogeneous Fe – Mn – C melt was understood as presence of dispersed Fe – C particles in it, which are suspended in Mn – C environment and separated from it by interface. Hypothesis of microheterogeneous state of Fe – Mn – C melts is supported by numerous experimental data on their thermodynamic and physical properties. Identification of anomalies in temperature dependences of physical properties of Fe – Mn – C melts made it possible to determine temperature values above which the melt superheating treatment (MST) leads to destruction of microheterogeneity, i.e., the liquid – liquid structure transition (LLT) in the melt. LLT is understood by authors as a structural transition “microheterogeneous melt – homogeneous solution” and this is expressed in destruction of microheterogeneous state when the melt is heated to a temperature determined for each composition (MST). This paper describes a method for theoretical determination of temperature range where microheterogeneous state of the Fe – Mn – C melt is thermodynamically stable. Thermodynamic stability of dispersed Fe – C particles in the Mn – C medium was estimated according to the equations proposed by Kaptay for a regular solution. It was assumed that interface between the melt of dispersed Fe – C particles with sizes from 2 to 34 nm, distributed in the Mn – C dispersion medium and separated from it by an interface with increased carbon content. This result of the assessment is consistent with the data on size of the structural units of a viscous flow obtained earlier within framework of the theory of absolute reaction rates.

Kinematic Viscosity and Electrical Resistivity of a Multicomponent Melt due to Liquid–Liquid Structure Transition

We investigated the kinematic viscosity and electrical resistivity of the multicomponent Fe74Cu1Nb1.5Mo1.5B8.5Si13.5 melt during three heating–cooling cycles. The temperature dependence of kinematic viscosity and electrical resistivity have the anomalous zones in the same temperature range and they are associated with the liquid–liquid structure transition (LLST). The anomalies were explained by changes in the activation energy and the cluster size. As the cluster size decreases, the activation energy decreases, but the viscosity and electrical resistance increase. LLST begins with the cluster dissolution, and as a result, the Arrhenius plot becomes nonlinear in the transition temperature range. After three cycles of heating–cooling, the temperature dependences of the kinematic viscosity and electrical resistance did not qualitatively change, and this allows us to conclude that LLST is thermoreversible. With an increase in the number of thermal cycles, the activation energy of viscous flow decreases, as well as the onset temperature and temperature range of LLST.

The Effect of Nickel on the Viscosity of Iron-Based Multicomponent Melts

In this work, we investigated the temperature dependence of the kinematic viscosity of multicomponent Fe72.5−xNixCu1Nb2Mo1.5Si14B9 melts with a Ni content of up to 12.7 at. %. The peculiarities of the temperature dependence of Ni-containing melts were explained by the tendency of Ni atoms to surface segregation. Ni atoms are concentrated near the interfaces of the liquid and solid phases in the mushy zone at the stage of melting and restrain the melting of the solid phase. With increasing Ni content, the Arrhenius type of viscous flow begins at a higher temperature. Ni atoms are concentrated at the periphery of clusters, increasing their size and decreasing their mobility. The movement of Ni-containing clusters increases the activation energy and decreases the kinematic viscosity. The change in the activation energy at a temperature of about 1700 K was associated with a liquid-liquid structure transition (LLST). This structural transition is reversible since it is observed both at the heating and cooling stages. The increase in kinematic viscosity at temperatures above 1900 K was associated with the decomposition of high-temperature clusters based on cementite and silicon oxides.

Effect of melt temperature on primary crystallization and thermal stability of Al86Ni6Y4.5Co2La1.5 metallic glass

In this paper, the correlations between the melt temperature of Al86Ni6Y4.5Co2La1.5 alloy and its crystallization behavior were studied. The results of differential scanning calorimetry (DSC) showed that the primary crystallization of Al86Ni6Y4.5Co2La1.5 alloy was greatly affected by the melt temperature: compared with the amorphous ribbons prepared at 1373 K and 1673K, the primary crystallization of the ribbons prepared at 1523 K was significantly advanced; The calculation of the activation energy indicated that the amorphous ribbon prepared at 1523 K has a lower energy barrier to be overcome during the first crystallization stage, which means that its thermal stability is worse, and fcc-Al is more likely to be precipitated; Abnormal melt structural changes were observed by electrical resistivity(ER), and liquid-liquid structure transition(LLST) occurred after 1402 K, which can be proved by the results of x-ray diffraction (XRD); Compared with the amorphous ribbons prepared at 1523 K and 1673K, the one prepared at 1373 K were more likely to precipitate intermetallic compounds during crystallization, which may be related to the disappearance of some atomic clusters caused by the increase of melt temperature.

Microstructure and properties of Sn-3.8Ag-0.7Cu-xCe lead-free solders with liquid-liquid structure transition and Ce addition**This work was supported by Guangdong Province Science and Technology Project (2016B090927008), the high-level leading talent introduction program of GDAS (project number 2016GDASRC-0106) and GuangZhou Science and Technology Project (201707010480).

Our previous work suggested that the Sn-3.8Ag-0.7Cu-xCe (x takes 0%, 0.2%, 0.5% and 1.0wt%) solder melt experienced a temperature-induced liquid-liquid structure transition (L-LST) which was reversible during two heating and cooling cycles far above the liquidus. In this work, the effects of liquid state manipulations and rare earth element Ce addition on solidified Sn-3.8Ag-0.7Cu-xCe structures and properties were investigated. The results revealed that the microstructure was remarkably refined, the spread ability and the shear strength were enhanced when the melt experienced L-LST and Ce addition. Meanwhile, 0.2 wt% Ce addition showed the most homogenous microstructure, leading to better properties. This work elicited that melt manipulations and Ce addition could be an effective way to optimize microstructure and properties of Sn-3.8Ag-0.7Cu-xCe soldered joints.

Composition dependent characteristic transition temperatures of Co-B melts

The temperature-dependent liquid structures of Co-B melts were studied by in-situ measuring the magnetization. A magnetization anomaly in term of the non-Curie-Weiss temperature dependence of magnetization was observed in the overheated state, demonstrating a temperature-induced liquid-liquid structure transition. This anomalous behavior was found to be a universal formula for the Co-B binary alloy system. The transition point (T0) and two paramagnetic Curie temperatures (θp(LI), θp(LII)) corresponding to two distinct kinds of liquids (i.e., high-magnetization liquid (HML) I and low-magnetization liquid (LML) II) were measured. With the increased concentration of Co, T0, θp(LI) and θp(LII) shift to higher temperatures and the Curie constants for the HML and LML decrease. Based on the location of T0, a guideline is drawn above the liquidus in the Co-B phase diagram, which could provide a significant guidance to the practical melt treatment.

Temperature-induced structure transition in a liquid Co-B eutectic alloy

The structure of metallic melt is not homogeneous and liquid–liquid structure transition (LLST) widely exists which can make strong influence on the subsequent solidification process. Here we report an experimental evidence of temperature induced LLST in a Co-B eutectic melt by in-situ measuring the magnetization within a wide temperature range under high magnetic fields. A transition point (T0) and two paramagnetic Curie temperatures (ϑp(L1), ϑp(L2)) corresponding to two different structures of the liquids are determined. The effects of magnetic field intensity on the LLST and paramagnetic curie temperatures are studied, and T0 and ϑp(L2) are found not sensitive to the field intensity, whereas, ϑp(L1) shifts to lower temperatures with the increasing magnetic field intensity.

Liquid-liquid structure transition and its effect on the solidification behaviors and microstructure of Sn75Bi25 alloy

This paper studied the liquid–liquid structure transition (L-LST) of Sn75Bi25 alloy with atom percentage via two direct methods such as a high temperature X-ray diffractometer and a modified high temperature Hall effect instrument as well as several indirect methods including resistivity, density, viscosity and thermal analysis methods. The results indicated that the reversible first-order liquid–liquid structure transition did occur in the range from 990 to 1068 K during heating and occur in the range from 865 to 945 K during cooling. From the atomic and molecular scale, the nature of the L-LST was the breaking of the residual covalent bonds and the cooperative rearrangement of atoms during heating. In addition, the breaking of the residual covalent bonds occurred not only during the L-LST but also before and after the L-LST. The L-LST reflected a qualitative change of melt structure. From the view of the electronic structure, the nature of the L-LST was the releasement of free electrons and the localized-extended transition of electron. Besides, a novel strategy combining atomic structure and electronic structure was developed to reveal the nature of the L-LST. The influences of the L-LST on the solidification behaviors and morphologies of Sn75Bi25 alloy also were investigated. The results showed that the undercooling of the eutectic phase increased after the L-LST, which was responsible for the drastic decrease in the spacing of the eutectic phase.

Dependence of Solidification for Bi2Te3\u2212xSex Alloys on Their Liquid States

The resistivity versus temperature (ρ-T) behaviours of liquid n-type Bi2Te3−xSex (x = 0.3, 0.45 and 0.6) alloys are explored up to 1050 °C. A clear hump is observed on all ρ-T curves of the three studied Bi2Te3−xSex melts during the heating process, which suggests that a temperature-induced liquid-liquid structural transition takes place in the melts. Based on this information, the solidification behaviours and microstructures of the alloys with different liquid states are investigated. The samples that experienced liquid structural transition show that the nucleation and growth undercooling degrees are conspicuously enlarged and the solidification time is shortened. As a result, the solidified lamellae are refined and homogenized, the prevalence of low-angle grain boundaries between these lamellae is increased, and the Vicker Hardness is enhanced. Atom probe tomography analyses prove that there is no segregation or nanoprecipitation within the grains, but the Te-rich eutectic structure and the evolution of composition near the Te-matrix phase boundary are investigated in a sample that experienced liquid structural transition. Our work implies that the solidification behaviours of Bi2Te3−xSex alloys are strongly related to their parent liquid states, providing an alternative approach to tailor the thermoelectric and mechanical properties even when only a simple solidification process is performed.

Optimizing microstructures and mechanical properties of hypereutectic Al-18%Si alloy via manipulating its parent liquid state

Liquid state manipulations on solidified Al-18%Si structures and properties were investigated based on its liquid abnormal resistivity-temperature behaviors (LARTB), which suggested a temperature-induced liquid-liquid structural transition (TI-LLST). The primary Si crystals are dramatically refined if solidified from the melt after LARTB range, compared with those before and during it. And then, solidified structures are further ameliorated by suitably mixing the high-temperature melt with low-temperature melt in semisolid state, generating increased tensile strength and ductility synchronously. This work elicits that liquid manipulations for optimizing materials structures and properties can be more effective if information suggesting TI-LLST is detected beforehand.

Effect of liquid–liquid structure transition on solidification of Sn57Bi43 alloy

In this paper, the effect of the liquid–liquid structure transition (L-LST) on the solidification behaviors and morphologies of Sn57Bi43 alloy was further studied. The liquid structure of Sn57Bi43 was studied with resistivity, thermal analysis and viscosity method. The obvious turning point is observed on resistivity–temperature, DSC and viscosity–temperature curves of Sn57Bi43 alloy. The resistivity increases linearly with increasing temperature before the turning point. These results indicate that temperature-induced liquid–liquid structure transition occurs at 943–1093 K and is reversible, which may be formed by large cooperative motions for molecular rearrangements. What is more, the results show that the undercooling of the eutectic phase increases and the microstructure becomes finer after solidifying from the melt experiencing L-LST. The spacing of eutectic phase decreases markedly. Based on these results explored the melt structure from different aspects, the nature of discontinuity of structural phase transition can be explored and the effect of L-LST on solidification of Sn57Bi43 alloy is studied.

Effect of liquid–liquid structure transition on the nucleation in undercooled Co–Sn eutectic alloy

The effect of liquid–liquid structural transition (LLST) on the undercoolability of liquid Co–Sn eutectic alloy has been investigated via cyclic overheating and undercooling. Results show that the stable undercooling increases considerably when the melt is overheated above a critical overheating temperature. The LLST is evidenced by differential scanning calorimetry (DSC) experiment and is thought to be the major factor for the sharp increase of undercooling at the critical point. The effect of LLST on undercooling is analyzed quantitatively within classical nucleation theory.

Temperature-Induced Liquid-Liquid Transition in Metallic Melts: A Brief Review on the New Physical Phenomenon

Understanding the nature of liquid structures and properties remains an open problem for many fundamental and applied fields. It is well known that there is no other defined phase line above liquidus (TL) in phase diagrams of ordinary alloys. However, via resorts of internal friction, electric resistivity, thermal analysis, X-ray diffraction, solidification, etc., the results of our research on lots of single- and multiple-component melts show a novel physical image: temperature induced liquid-liquid structure transition (TI-LLST) can occur above TL. Moreover, the solidification behaviors and structures out of the melts that experienced TI-LLST are distinct from those out of the melts before TI-LLST. In this paper, some typical examples of TI-LLST and characteristic aspects of the TI-LLST are briefly reviewed, in which the main contents are limited in our own achievements, although other groups have also observed similar phenomena using different methods. In the sense of phenomenology, TI-LLST reported here is quite different from other recognized liquid transitions, i.e., there are only a few convincing cases of liquid P, Si, C, H2O, Al2O3-Y2O3, etc. in which the transition occurs, either induced by pressure or at a supercooled state and near liquidus.

Liquid–liquid structure transition in Sn–3.5Ag–3.5Bi melts

The liquid–liquid structure transition (LLST) as the function of temperature and time in Sn–3.5Ag–3.5Bi melts was investigated with the help of direct current four-probe method. The LLST which occurs during first cycle heating of two cycles heating/cooling experiments can divide into two different structure changes: irreversible LLST of 650°C isothermal and step reversible LLST at 770°C–806°C on subsequent heating process. Obvious kinetic phenomena are observed during isothermal experiments. Irreversible and reversible LLST are analysed from the viewpoint of short-range order. These results will help to understand the law and mechanism of liquid field, and provide some scientific reference for the innovation of lead-free solder manufacturing.

Dependence of GFA and Crystallization Behaviors of Al86Ni9La5 Metallic Glass on Its Original Liquid State

AbstractDuring the heating process the temperature‐induced liquid–liquid structure transition (LLST) of Al86Ni9La5 melt from 1320 to 1490 K was identified by both electrical resistivity and differential thermal analysis measurement. The effects of liquid structural change on the crystallization behavior and glass forming ability (GFA) of Al86Ni9La5 alloy were investigated. The amorphous samples prepared at different melt temperatures according to the liquid states were obtained. The results showed that the formation of intermetallic compounds during the crystallization process of the samples prepared below and within the LLST temperature range was earlier than that prepared above the LLST temperature range. The sample prepared above the LLST temperature range had the lowest GFA.

Control of the phase composition and morphology of a Cu-Sb eutectic alloy via liquid-liquid structure transition

The current paper focuses on the solidification characteristics of a Cu-Sb eutectic alloy in its different liquid states. Liquid alloy resistivity-temperature patterns suggest an irreversible temperature-induced liquid-liquid structure transition (TI-LLST), and a reversible TI-LLST occurred during the heating-cooling runs. A set of solidification experiments was conducted based on the results. The irreversible TI-LLST caused an enhanced solidification undercooling, increased solidification rate, refined regular eutectic morphologies, and absence of a pre-eutectic Cu2Sb phase. The reversible TI-LLST resulted in different phase compositions and eutectic structures. The mechanisms behind these transitions are also briefly discussed.

Liquid-Liquid Structure Transition and its Effects on Solidification Behavior of Binary Alloys

In our work, some anomalous changes, namely the temperature-induced liquid-liquid structure transitions, were observed at the temperature hundreds degrees above the corresponding liquidus in some binary alloys. Based on the results of liquid structure transitions, corresponding solidification experiments have been carried out on the alloys melted and held at the temperature above or under the liquid-liquid structure transition (L-LST), respectively. It is found that L-LST has a significant effect on solidification behavior and microstructure. There is a general rule that the super-cooling degree increases and the microstructure becomes finer cast from the liquid experienced L-LST.