Solidification Of Liquid Metal Research Articles

Simultaneously improving thermal conductivity, mechanical properties and metal fluidity through Cu alloying in Mg-Zn-based alloys

Mg-Zn-based alloys have been widely used in computer, communication, and consumer (3C) products due to excellent thermal conductivity. However, it is still a challenge to balance their mechanical performance and thermal conductivity. Here, we investigate microstructure, mechanical performance, thermal conductivity and metal fluidity of Mg-5Zn (wt.%) alloy after Cu alloying by experimental and simulation methods. First, Mg-5Zn alloy consist of α-Mg matrix and interdendritic MgZn phases. As the Cu content increases, however, MgZn phases disappear but intragranular Mg2Cu and interdendritic MgZnCu phases appear in Mg-5Zn-Cu alloys. Besides, the grain size of α-Mg phase is refined and the volume fraction of MgZnCu phase increases as the Cu content increases. Second, Cu addition is found to improve thermal conductivity of Mg-5Zn alloy remarkably. Especially, Mg-5Zn-4Cu alloy exhibits the best thermal conductivity of 124 W/(m·K), which is mainly due to the significant reduction in both solid solubility of Zn in the α-Mg matrix and lattice distortion of α-Mg matrix. Moreover, a stable crystal structure of MgZnCu phase also contributes to an increased thermal conductivity based on first principles and molecular dynamics simulations. Third, Cu addition simultaneously enhances strength and ductility of Mg-5Zn alloy. Tensile yield strength and elongation of Mg-5Zn-6Cu alloy reach 117 MPa and 18.0 %, respectively, which is a combined result of refinement, solution, second phase, and dislocation strengthening. Finally, combined with a phase field simulation, we found that Cu addition enhances metal fluidity of Mg-5Zn alloy. On the one hand, Cu alloying not only delays dendrite growth but also prolongs solidification time. On the other hand, MgZnCu phase stabilizes the dendrite growth of the α-Mg phases by reducing energy consumption during solidification of liquid metal. This work demonstrates that Cu alloying is an ideal strategy for synergistically improving the thermal conductivity, mechanical performance and metal fluidity of Mg-based alloys.

Stretchable stiffness-tuning of liquid metal elastomer triggered by homocrystal seeds

The hybrid structure of liquid metal units and organic elastomer has huge potential in achieving stretchable and reversible stiffness regulation, while such tuning is often restrained by high energy consumption for liquid metal solidification. Here, we conceive to solve the above challenge through introducing the fully leveraging interaction between supercooled liquid metal and homocrystal seeds within silicone elastomer. It is disclosed that the supercooled liquid metal-elastomer can maintain an extremely stable soft state until the supercooling is eliminated by modulating the mechanical force and elastomer deformation. This circumvents the utilization of intricate refrigeration equipment and offers a highly efficient and concise strategy for stiffness regulation. Moreover, conceptual experiments were performed to demonstrate the practical values of this technology through designing and testing the new shape memory materials, temperature-sensitive switches, and controlled circuits. The solidification mechanisms of supercooled Ga triggered by homocrystal seeds were interpreted. Overall, the present finding has generalized purposes and holds promise to significantly extend the theoretical and technological categories of classical stiffness tunable materials.

Microstructure and mechanical properties of 304 stainless steel produced by interpass milling hybrid direct energy deposition-arc

Good surface forming accuracy is an important indicator for evaluating the quality of the additive components, especially for complex components that require high surface forming accuracy, and the regulation of microstructure and properties has a very important impact on metal processing and manufacturing. In this study, an experimental device for interpass milling hybrid direct energy deposition-arc was developed. Combined with the simulation method, the effect of interpass milling on the forming accuracy was deeply studied from the liquid metal's force and flow behavior. The changes in microstructure and properties were also studied in depth from the evolution mechanism of residual stress and the solidification of liquid metal, thereby enhancing the controllability of the forming and properties of stainless steel additive components. The results showed that the addition of interpass milling refined the grains, weakened the orientation texture of the <001> crystal plane, and significantly improved the uniformity of the microstructure. Finally, the additive component with the best mechanical properties was obtained at a milling depth of 200 μm, with a 31.8 % increase in microhardness, 14.9 %, and 59.2 % increase in tensile strength and elongation, respectively. The anisotropy to isotropy of the deposited sample was transformed.

Experimental and numerical analysis of impingement temperature effect on the sacrificial plate's hole formation during nuclear severe accident

Liquid metal breaching onto a metal plate is an important aspect that needs to be considered in the nuclear severe accident analysis. This relates to the downward relocation of molten material to the supporting system such as sacrificial grid plate and lower head while accident happened. The molten core material impinged the sacrificial grid plate which was quenched before interacted with reactor pressure vessel. The present study aims to investigate the dynamic behaviors of holes formation due to liquid metal jet impingement onto a metal plate at initial temperatures 423 K, 473 K, and 523 K. The experiments and numerical simulation were performed with molten Wood's Metal and 5 mm thickness of Lead Bismuth Eutectic plates. The modified Moving Particle Semi-Implicit method was used to perform the numerical calculation based on the particle movement. The results showed that the plate was locally melted by the heat supplied from the liquid metal jet and induced the penetration. A larger amount of liquid metal stayed, then liquid metal pool was formed when the liquid temperature jet was lower. The temperature variation resulted unsignificant change of hole size diameter on both surfaces. The formed hole sizes in the plate's top and bottom surfaces were around 5.7–14 mm and 3.7−5 mm, respectively. The required time for the liquid metal penetration was shorter when the liquid metal temperature was higher. The increase of conduction heat transfer during the solidification of liquid metal could decrease the Nusselt number at the stagnation zone. The findings show that the experiment and numerical results can predict the sacrificial grid plate's hole formation and dynamic mechanism within critical time of molten core material impingement.

Sodium-Based Concave Metasurfaces for High Performing Plasmonic Optical Filters by Templated Spin-on-Sodiophobic-Glass.

Optical filters have aroused tremendous excitement in advanced photonic instruments and modern digital displays due to their flexible capability of spectrum manipulation. Plasmonic metasurfaces of narrow bandwidth, high spectral contrast, and robust structure tolerance are highly desired for optical filtration (especially in the visible regime) but rather challenging as large spectral broadening from intrinsic ohmic loss and design/fabrication deviations. Here the high-performing sodium-based metasurfaces are demonstrated for optical filtration across 450 to 750nm by unique structure design of spatially decoupled concave surfaces and precise fabrication through templated solidification of liquid metals. Thanks to the distinct suppression of metallic loss as well as fabrication tolerance of interfacial structures, the as-prepared concave metasurfaces enable a minimum linewidth of ≈15nm, a maximal optical contrast of ≈93%, and a high measure-to-design spectral match ratio ≈1500. These results have for the first time pushed the operation wavelengths of sodium-based plasmonic devices from infrared to visible which in turn demonstrates the capability of filling the blank of commercial dielectric optical filters thus far.

The interface microstructure and phase constitution of Nb/316L composite plates fabricated by explosive welding

ABSTRACT Niobium has a reputation for its superior superconducting, high strength and corrosion resistance at elevated temperatures. In this work, the explosive welding technique was successfully performed to join Nb/316L dissimilar metals. To reveal the phase constitution and texture distribution at the joining interface, the EBSD test was carried out. It was concluded that an irregular large wavy structure of fine crystal, sub-grains and twin structures was formed. In addition, the recrystallised structures, substructures, deformed structures and local internal stress at the joining interface were attributed to severe plastic deformation and rapid solidification of liquid metal. Furthermore, six different deformation textures and recrystallisation textures were confirmed at the joining interface due to severe plastic deformation and dynamic recrystallisation.

Experimental and numerical investigations on interface microstructure characteristics and wave formation mechanism of Sn/Cu explosive welded plates

ABSTRACT The interface characteristics and formation mechanism of explosive welded waveform structures still lack a detailed and in-depth research. Thus, a combination of advanced characterization and numerical simulation methods were performed in this study to investigate the phase constitution, texture distribution, 3D interface morphology and wave formation mechanism of Sn/Cu explosive welded interface. The microstructure analyses indicated that the typical waveform structures composed of fine crystal band and elongated grains zone were formed at the Sn/Cu joining interface. The dynamic recrystallized structures and local high strain at the waveform were attributed to severe rheological deformation and rapid solidification of liquid metals. In addition, the S, copper, brass and fiber deformation textures and the cube and gross recrystallization textures were found. The CT results indicated the 3D Sn/Cu joining interface morphology presents a regular convex waveform feature, which is related to periodic pulse load caused by explosive detonation. Furthermore, based on the simulation results, the 2D joining interface presents similar experimental waveform structure, and the 3D interface evolution characteristic was consistent with the shock wave propagation characteristics on the flying plate to some extent, which was in good agreement with the experimental results.

Origin of the superchondritic carbon/nitrogen ratio of the bulk silicate Earth – an outlook from iron meteorites

Disagreement regarding the origin of the bulk silicate Earth’s (BSE) superchondritic carbon/nitrogen (C/N) ratio is due, in part, to the unknown C/N ratios of differentiated planetesimals – the building blocks of Earth-like rocky planets. In this study we report solid–liquid metal partitioning experiments for C and N that allow us to reconstruct, from the C and N contents of iron meteorites, the C/N ratios of the cores of the earliest formed planetesimals. Due to their siderophile character, most of the C and N retained in these bodies after differentiation resides in their cores. Therefore, estimates of the bulk C and N contents and C/N ratios of the cores yield confident estimates of these quantities in the complete parent bodies of iron meteorites. Our experimental data, at 1 GPa and 1200–1400 °C, show that C and N are incompatible in solid metal relative to S-poor liquids but compatible in solid metal relative to S-rich liquids. Crucially, N is approximately an order of magnitude more compatible than C in S-rich systems. S itself is incompatible in solid metal and so the late-crystallizing liquids persisting at the end of core freezing were S-rich for most cores. Although these late-crystallizing liquids are unsampled by iron meteorites, we infer that their N contents and C/N ratios were generally lower and higher, respectively, than those in iron meteorites. Depending upon the fraction of unsampled late-crystallizing liquids as well as their S contents, the C/N ratios of the bulk cores and complete parent bodies are either similar to or higher than those measured in iron meteorites. The reconstructed C/N ratios of most of the parent bodies of iron meteorites are chondritic, except that the volatile-rich IC and IIC groups have superchondritic C/N ratios. Importantly, the C/N ratio of the parent body of the IC iron meteorite group lies within the estimated range of the BSE, whereas the C/N ratios of all other groups are lower. Correlated depletion of moderately volatile elements like Ge and Ga with C and N, variations in metallographic cooling rates, and Pd-Ag isotope systematics suggest that the parent cores of the volatile-depleted iron meteorite groups were likely affected by volatile degassing. If volatile-rich iron meteorite groups like the IC better capture the C and N inventories of the parent cores of the earliest formed planetesimals, then delivery of C and N via such planetesimals makes the superchondritic C/N ratio of the BSE a natural consequence of the Earth’s accretion history. Otherwise, poorly constrained processes like atmospheric erosion or C and N delivery by exotic materials are required to explain the superchondritic C/N ratio of the BSE.

Thermal Interface Materials with High Thermal Conductivity and Low Young's Modulus Using a Solid-Liquid Metal Codoping Strategy.

Thermal interface materials (TIMs), as typical thermal functional materials, are highly required to possess both high thermal conductivity and low Young's modulus. However, the naturally synchronized change in the thermal and mechanical properties seriously hinders the development of high-performance TIMs. To tackle such a dilemma, a strategy of codoping solid fillers and liquid metal fillers into polymer substrates is proposed in this study. This strategy includes a large amount of liquid metals that play the role of thermal paths and a small amount of uniformly dispersed solid fillers that further enhance heat conduction. Through the synergistic effect of the liquid metal and solid fillers, the thermal conductivity can be improved, and Young's modulus can be kept small simultaneously. A typical TIM with a volume of 55% gallium-based liquid metal and 15% copper particles as fillers has a thermal conductivity of 3.94 W/(m·K) and a Young's modulus of 699 kPa, which had the maximum thermomechanical performance coefficient compared with liquid metal TIMs and solid filler-doped TIMs. In addition, the thermal conductivity of the solid-liquid metal codoped TIM increased sharply with an increase of liquid metal content, and Young's modulus increased rapidly with an increase of the volume ratio of copper and polymer. The high-low-temperature cycling test and large-size light-emitting diode (LED) application demonstrated that this TIM had stable physical performance. The synergistic effect of the solid fillers and liquid metal fillers provides a broad space to solve the classic tradeoff issue of the mechanical and thermal properties of composites.

Индукционный метод локализации фронта кристаллизации

The paper describes the development and testing of an inductive sensor designed for determining the position of the solidification front of electricallyconductive melts. The operation of the sensor is based on the eddy current transducer principle. We compared induction and ultrasonic methods of localizing the solidification front of a gallium alloy on a model problem of directional solidification of liquid metal in a flat vertical layer. The principles of the induction method are described, its ap-plicability is shown, the measurement error has been found.

Numerical Analysis of Temperature Distribution in Tandem Welding Process

In this study, the numerical solutions for the steady-state heat conduction problem with uniform heat source, the steady-state heat conduction problem with convective heat transfer and the transient heat conduction problem have been developed using finite difference method. These numerical solutions have been validated with analytical solutions. After observing the good agreements between numerical solutions and analytical solutions, these three different problems combined to simulate the tandem welding process. The first objective of this study is to present a numerical simulator for the transient heat conduction problem that includes non-uniform moving heat sources and convective heat transfer term. This numerical simulator contains explicit and implicit time discretization methods. In this simulator, it is possible to change the grid sizes, time step sizes, total simulation time, distance between electrodes, magnitude of the sources' power, speed of the sources, etc. Secondly, the temperature distribution of single and twin wire welding processes have been compared using proposed numerical simulator to investigate the premature solidification of liquid metal in low-temperature zone of molten pool. Thirdly, experimental study was carried out using Fluke Thermal Imager to validate numerical results. It was obtained that the maximum temperature of numerical result is very close to the maximum temperature of experimental result with 0.248 % error. Finally, the all Matlab codes related to developed numerical simulator have been added to Appendix to facilitate other researchers’ work.

Phase constitution and texture distribution in the vortex zone of Co/Cu explosive welded plates

Cobalt has a reputation for its excellent electrical and magnetic properties, and exceptional wear and corrosion resistance, which has many applications in the batteries, electronic industry and semiconductor industry. In this work, the explosive welding technique was successfully performed to join Co/Cu dissimilar metals. To reveal the phase constitution and texture distribution of the vortex zone at Co/Cu joining interface, the electron backscatter diffraction (EBSD) test was carried out. It was concluded that the typical vortex structure composed of fine crystal band, sub-grains and twin structures was formed at the Co/Cu joining interface. In addition, the dynamic recrystallized structure and local internal stress at the vortex was attributed to severe plastic deformation and rapid solidification of liquid metals resulted from high strain state collision. Furthermore, the S, copper, brass and fiber deformation textures and the cube and gross recrystallization textures were confirmed at the vortex zone due to plastic deformation and dynamic recrystallization.

Oscillatory bifurcation patterns initiated by seeded surface solidification of liquid metals

Oscillatory bifurcation patterns initiated by seeded surface solidification of liquid metals

Liquid metal enabled continuous flow reactor: A proof-of-concept

Liquid metal enabled continuous flow reactor: A proof-of-concept

Suppression mechanism of weld appearance defects in tandem TIG welding by numerical modeling

In high-speed tungsten inert gas (TIG) welding, the premature solidification of liquid metal in low-temperature zone of molten pool results in the formation of weld appearance defects (WADs) such as undercut and humping weld. Tandem TIG welding was developed to prevent the formation of the WADs and realize high-speed welding. A three-dimensional model of arc and molten pool was developed to investigate the heat and mass transfer behavior in molten pool of tandem TIG welding process. The results indicate that, because of the thermo-mechanical control effect on the molten pool by the assistant TIG arc, a stable swelling zone forms between the two arcs and the formation of trail accumulation was prevented. The maximum backward velocity driven by the main TIG arc is decreased significantly, which suppresses the backward flow and premature solidification of liquid metal. The existence time of liquid metal is evidently longer by 70% than that of single TIG welding, which leads to the liquid flow at the tail of weld pool sufficiently moving forward to suppress the instability of depression zone. The heat and mass transfer in molten pool indicates that during tandem TIG welding process, the thermo-mechanical effect of assistant TIG arc prolongs the existence time of liquid metal and improves its flowing back, so the WADs were efficiently suppressed.

Scalable Synthesis of High Entropy Alloy Nanoparticles by Microwave Heating

High entropy alloy nanoparticles (HEA-NPs) are reported to have superior performance in catalysis, energy storage, and conversion due to the broad range of elements that can be incorporated in these materials, enabling tunable activity, excellent thermal and chemical stability, and a synergistic catalytic effect. However, scaling the manufacturing of HEA-NPs with uniform particle size and homogeneous elemental distribution efficiently is still a challenge due to the required critical synthetic conditions where high temperature is typically involved. In this work, we demonstrate an efficient and scalable microwave heating method using carbon-based materials as substrates to fabricate HEA-NPs with uniform particle size. Due to the abundant functional group defects that can absorb microwave efficiently, reduced graphene oxide is employed as a model substrate to produce an average temperature reaching as high as ∼1850 K within seconds. As a proof-of-concept, we utilize this rapid, high-temperature heating process to synthesize PtPdFeCoNi HEA-NPs, which exhibit an average particle size of ∼12 nm and uniform elemental mixing resulting from decomposition nearly at the same time and liquid metal solidification without diffusion. Various carbon-based materials can also be employed as substrates, including one-dimensional carbon nanofibers and three-dimensional carbonized wood, which can achieve temperatures of >1400 K. This facile and efficient microwave heating method is also compatible with the roll-to-roll process, providing a feasible route for scalable HEA-NPs manufacturing.

The enhanced light diffuse reflection of laser marking Al substrate for the back reflector purpose

This study set out with the aim of assessing the possibilities of incorporating the laser marking strategies for the purpose of diffuse back reflector fabrication. The correlation between the laser process parameters of fabricated samples’ microstructure and their optical properties has been determined. The laser texturizing was conducted on the aluminum substrate throughout the Nd:YAG (1064 nm) laser varying the laser process parameters, i.e. scanning speed (v) and pulse repetition rate (f). The effect of laser irradiation on surface nanostructure was investigated by means of confocal optical microscopy (COM) and scanning electron microscopy (SEM). In order to evaluate the phase composition and optical properties of fabricated nanotextures, the X-ray diffraction (XRD) and spectrophotometric measurements were performed. The obtained reflectance spectra of samples were used to perform the colorimetry analysis and calculate the luminous reflectance. The morphological evaluation of patterned surfaces gives evidence of periodic crater-shaped structures formation influenced by chaotic radial-ligaments patterns resulting from splashing liquid metal solidification. Laser-textured Al reflectors show almost similar total reflectance as the untreated substrate whereas the significant enhancement of diffuse reflectance of patterned sample series can be observed. The different hues of white colour appear on all laser-patterned Al surfaces. The calculated luminous reflectance of proceeded samples ranging from 65% to 75%. The overall results show the effectiveness of the laser marking process in order to obtain highly diffusive scattering layers on Al substrate without employing any additional coating.

Modeling the pressure-dependent melting temperature of metals

We present a model of pressure-dependent melting temperature to describe the physical fact that both cooling and pressurization can cause the solidification of liquid metal. Based on the Force-Heat Equivalence Energy Density Principle, an equivalent relationship between the heat energy variations during cooling and the mechanical work during pressurization is established as the molten metal solidifies. Then, this equivalent relationship is applied to develop a pressure-dependent melting temperature model without any adjustable parameter for metals. The model reveals the inner relationship between melting temperature, pressure, the bulk modulus and its first pressure derivative at zero pressure. The predicted results by our model are in good agreement with the available experimental data. Moreover, this study provides insights into the fundamental understanding of quantitative effect of pressure on melting temperature, which is in contrast to the well-known Lindemann's and Simon's equations that are both empirical melting temperature equations. It is worth noting that the melting curve of metals to very high pressure can be well predicted by our model only needing two experimental data at low pressures.

The glass transition during liquid metal solidification exemplified by a Zr-based glass-forming alloy: Experiments and numerical simulations

By using Zr41.2Ti13.8Ni10Cu12.5Be22.5 (Vit1) bulk metallic glass with a defined cooling history, the heat capacity (Cp) of liquid and glass, and the calorimetric glass transition in differential scanning calorimetry experiments were investigated. Then, a thermal equilibrium model related to the melting and solidifying process was established to extrapolate the solidification glass transition (SGT) temperature range during liquid to glassy solid phase transformation. By using the extrapolated SGT temperature range, the thermodynamic parameters, including the Cp and thermal conductivity (λ), were adjusted, which can make the simulated cooling temperature curves accurately reflect the recorded ones. The coincidence of experimental and simulation results indicates the rationality of the thermal equilibrium model established in the present work. Furthermore, it is proposed that the SGT is resulted from the falling out-of-equilibrium of the undercooled liquid metal that acts as an endothermic trap to suppress the occurrence of recalescence.

Effect of combining continuous casting and simultaneous solidliquid metal deformation on the structure and properties of alloy V95 products

It is known that the solidification of melts under the influence of external factors leads to the formation of a fine-grained structure in the work pieces which improves the mechanical characteristics of finished metal products. The production of lengthy profiles with a high level of mechanical properties in a short production cycle is a complex interdisciplinary task of great practical importance. The paper presents results of research of the properties of products from aluminum alloy V95, which were obtained by continuous vertical casting combined with deformation in the solid-liquid state during solidification. A diagram of a device that implements such a process of combining is presented; its operation is reviewed. Also, a description is given of a method for producing flat work pieces and sample preparation for studying their mechanical characteristics and microstructure.As research shows the metal products have a fine-grained structure with a dense directional arrangement of dislocations. The grain boundaries are wide, uneven, consisting of grids and dislocation plexuses. During the melt solidification a thin directional dislocation structure is formed in the crystallizer of the device providing increase of the mechanical characteristics of metal products without additional processing, and there are no shrinkage defects. The possibility of obtaining long metal products with high mechanical characteristics for a short production cycle with reduced power costs was shown.