Search

Electromagnetic levitation of a liquid metal droplet is of great interest to study gas–liquid metal reactions. An important prerequisite for the evaluation of the overall mass transfer between the gas and metal is to characterize the geometry of the deforming molten droplet, which determines the interfacial reaction area. In this article, the free surface shape and dynamics of a molten 80%Ni–20%Cr droplet is investigated both experimentally and numerically. The frequencies associated to the oscillatory translational motions of the drop and to the vibrations of its free surface are measured using high-speed video image analysis. A 2D transient model is then presented, in which three interacting phenomena are considered: electromagnetic phenomena, the turbulent flow of liquid metal in the drop and the change in the drop shape. The numerical results presented demonstrate the capabilities of the model. [ABSTRACT FROM AUTHOR]

Pure, low-oxygen zirconium samples have been observed to nucleate a solid phase under conditions during which the sample was expected to remain liquid. This phenomenon was first seen during Spacelab Mission MSL-1R (materials science laboratory) experiments and has since also been observed in the International Space Station (ISS) electromagnetic levitation (EML) facility on a different sample. Current work has been able to replicate these anomalous solidification events under a range of conditions in the ISS MSL-EML facility. The solidification events are not well explained by classical homogeneous or heterogeneous nucleation. The current theory is that collapsing voids in the melt create a local region of high pressure that results in local material being deeply undercooled and a strong driving force for solidification. [ABSTRACT FROM AUTHOR]

The bulk metallic electromagnetic levitation technique has a promising application prospect in condensed physics and materials science. In order to resolve the problem of weak levitation force and the small size of samples, an optimized solution based on finite element analysis (FEA) is developed to seek the best electromagnetic field distribution in the levitation zone. The influence of material properties on the distribution of magnetic flux density, surface pressure, and the Lorentz force were studied by the FEA method with various sample sizes of titanium and copper balls. The levitation capability of cylindrical coil system which consists of a single-layer coil with an inner diameter of 30 mm and the levitated object with a diameter of 20 mm was analyzed. To keep a balance between the turn number and increment efficiency of force, the best number of 7 turns is confirmed. Then, two types of optimized coils were predicted by numerical simulations, and the levitation force is improved drastically. The double-layer coil displays an outstanding levitation capability owing to the strong electromagnetic field generated by multilayer turns. In addition, 5 to 50 g aluminum, titanium, copper, and nickel are levitated by the above three kinds of coils and the levitation capacities are validated from the recorded data of the minimum operating current that can levitate the samples. The experimental results show good agreements with the simulation results, and the minimum current for optimized coils is reduced efficiently. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) are advanced materials characterized by their unique and complex compositions. Characterized by a mixture of five or more elements in roughly equal atomic ratios, these alloys diverge from traditional alloy formulations that typically focus on one or two principal elements. This innovation has paved the way for subsequent studies that have expanded our understanding of HEAs, highlighting the role of high mixing entropy in stabilizing fewer phases than expected by traditional phase prediction methods like Gibbs's rule. In this review article, we trace the evolution of HEAs, discussing their synthesis, stability, and the influence of crystallographic structures on their properties. Additionally, we highlight the strength–ductility trade-off in HEAs and explore strategies to overcome this challenge. Moreover, we examine the diverse applications of HEAs in extreme conditions and their promise for future advancements in materials science. [ABSTRACT FROM AUTHOR]

The density and viscosity of ternary Cr-Fe-Ni liquid alloys have been investigated over a wide temperature range. The density was measured using electromagnetic levitation as a container-less technique, while viscosity was measured by means of a high-temperature oscillating cup viscometer. Although, the concentration dependence of density shows the influence of the second order (binary) interaction parameter in excess volume, the influence of a third order (ternary) interaction parameter in excess volume can be neglected. The temperature dependences of the viscosities are well described by the Arrhenius law. The viscosity increases monotonically as Fe or Cr concentration increases. For constant temperature, the viscosity as a function of iron molar faction can be described by a thermodynamic model using the enthalpy of mixing as input parameter. [ABSTRACT FROM AUTHOR]

Electromagnetic levitation was used to determine Cu–Nb phase diagram and to study supercooling effects on solidification characteristics of the alloys containing 5–70 wt% Nb. The Cu–Nb stable phase diagram was found to exhibit near-flat liquidus with a peritectic reaction at 1093 °C. Melt separation was found only for specimens containing approximately 20 wt% Nb. The results indicate that melt separation in the alloy requires supercooling exceeding 230 K combined with high cooling rates during solidification. Some specimens quenched from the solid + liquid zone on a copper chill also show evidence of melt separation which is attributed to minor oxygen impurities. Nb-rich liquid which nucleates below the T 0 curve solidifies as a metastable Nb-bcc lattice containing only 67 wt% Nb as compared to 96 wt% of the regular Nb dendrites. [ABSTRACT FROM AUTHOR]

The effects of supercooling and cooling rate on the microstructure of ternary Cu–Fe–Co alloys were investigated. Electromagnetic levitation was used to supercool the liquids down by 180 K. Alloys with 11 at.% Cu and less than 19 at.% Fe contained fcc (Fe, Co) and fcc Cu phases; those with 19 to 23 at.% Fe contained bcc (Fe, Co), fcc (Fe, Co) and fcc Cu; those with more than 23 at.% Fe contained bcc (Fe, Co) and fcc Cu. The primary dendrites contained 10 to 20 at.% Cu, with Fe and Co contents depending on the alloy composition. Supercooling the melt below a certain temperature resulted in metastable separation of the melt into two liquids, one (Co + Fe)-rich, the other Cu-rich. The metastable phase separation temperatures and the two liquid compositions were determined experimentaly, and compared with calculated ones. Isothermal cross-sections at various temperatures were constructed for stable and metastable cases based on thermodynamic and experimental data of the Cu–Co, Cu–Fe, and Co–Fe systems. A peritectic reaction for the ternary alloys was found at approximately 1100°C. [ABSTRACT FROM AUTHOR]

Materials science is highly significant in space program investigation, energy production and others. Therefore, designing, improving and predicting advanced material properties is a crucial necessity. The high temperature creep and corrosion resistance of Ni-based superalloys makes them important materials for turbine blades in aircraft engines and land-based power plants. The investment casting process of turbine blades is costly and time consuming, which makes process simulations a necessity. These simulations require fundamental models for the microstructure formation. In this paper, we present advanced analytical techniques in describing the microstructures obtained experimentally and analyzed on different sample's cross-sectional images. The samples have been processed on board the International Space Station using the MSL-EML device based on electromagnetic levitation principles. We applied several aspects of fractal analysis and obtained important results regarding fractals and Hausdorff dimensions related to the surface and structural characteristics of CMSX-10 samples. Using scanning electron microscopy (SEM), Zeiss LEO 1550, we analyzed the microstructure of samples solidified in space and successfully performed the fractal reconstruction of the sample's morphology. We extended the fractal analysis on the microscopic images based on samples solidified on earth and established new frontiers on the advanced structures prediction. [ABSTRACT FROM AUTHOR]

The article offers information on the field of high temperature thermophysics where only a few experimental methods deliver data from more than 1000 degrees above the melting point. It discusses that as in fast pulse-heating, the high temperature region is the focus of interest we consider that the results are worth being published as a compilation.

With the liquid phase being (more or less) transparent and the solid phase opaque, the use of such substances enables the time-dependent imaging of the solidification process, in this case in a Bridgman furnace that allows for well-controlled directional solidification in flat samples. The observed growth and pattern formation for the studied near-peritectic compositions and various processing conditions provide scientific insights into the solidification mechanisms in equivalent metallic peritectic alloy systems. Long-term experiments in microgravity have a long history - from the early days of spaceflight to current experiments onboard the International Space Station (ISS). [Extracted from the article]

High undercooling has been achieved in CoPd melts by employing the method of molten glass denucleating combined with cyclic superheating, and the microstructure evolution with undercooling was systematically investigated. Within the achieved range of undercooling, 0-415 K, two kinds of grain refinements have been observed in the solidification microstructures. The three critical undercoolings are 72, 95, and 142 K, respectively. When undercooling is less than 72 K, the coarse dendritic morphology is formed, which is similar to the conventional as-cast microstructure. The first grain refinement occured in the range of undercooling, 72-95 K can be attributed to the breakup of dendrite-skeleton owing to remelting. When undercooling locates within 95-142 K, highly developed directional fine dendrite can be obtained because the severe solute trapping weakens the effect of solute diffusion during the dendrite growth. The second grain refinement occurred when undercooling exceeds the critical undercooling (∆ T* = 142 K), the formation of fined equiaxed microstructure can be ascribed to the stress that originates from the extremely rapid solidification process, which resulted in the dendrite fragmentation finally. [ABSTRACT FROM AUTHOR]