Solidification Process Research Articles

Study on the Solidification and Heat Release Characteristics of Flexible Heat Storage Filled with PCM Composite

Phase change materials (PCMs) have significant potential for utilization due to their high energy storage density and excellent safety in energy storage. In this research, a flexible heat storage device using the stable supercooling of sodium acetate trihydrate composite is developed, enabling on-demand heat release through controlled solidification initiation. The solidification and heat release characteristics are investigated in experiments. The results indicate that the heat release characteristics of this heat storage device are closely linked to the crystallization process of the PCM. During the experiment, based on whether external intervention was needed for the solidification process, the PCM manifested two separate solidification modes—specifically, spontaneous self-solidification and triggered-solidification. Meanwhile, the heat release rates, temperature changes, and crystal morphologies were observed in the two solidification modes. Compared with spontaneous self-solidification, triggered-solidification achieved a higher peak surface temperature (53.6 °C vs. 46.2 °C) and reached 45 °C significantly faster (5 min vs. 15 min). Spontaneous self-solidification exhibited slower, uncontrollable heat release with dendritic crystals, while triggered-solidification provided rapid, controllable heat release with dense filamentous crystals. This controllable switching between modes offers key practical advantages, allowing the device to provide either rapid, high-power heat discharge or slower, sustained release as required by the application. According to the crystal solidification theory, the different supercooling degrees are the main reasons for the two solidification modes exhibiting different solidification characteristics. During solidification, the growth rate of SAT crystals exhibits substantial disparities across diverse experiments. In this research, the maximum axial growth rate is 2564 μm/s, and the maximum radial growth rate is 167 μm/s.

The Effect of Yttrium Addition on the Solidification Microstructure and Sigma Phase Precipitation Behavior of S32654 Super Austenitic Stainless Steel

This study focuses on S32654 super austenitic stainless steel (SASS) and systematically characterizes the morphology of the sigma (σ) phase and the segregation behavior of alloying elements in its as-cast microstructure. High-temperature confocal scanning laser microscopy (HT-CSLM) was employed to investigate the effect of the rare earth element yttrium (Y) on the solidification microstructure and σ phase precipitation behavior of SASS. The results show that the microstructure of SASS consists of austenite dendrites and interdendritic eutectoid structures. The eutectoid structures mainly comprise the σ phase and the γ2 phase, exhibiting lamellar or honeycomb-like morphologies. Regarding elemental distribution, molybdenum displays a “concave” distribution pattern within the dendrites, with lower concentrations at the center and higher concentrations at the sides; when Mo locally exceeds beyond a certain threshold, it easily induces the formation of eutectoid structures. Mo is the most significant segregating element, with a segregation ratio as high as 1.69. The formation mechanism of the σ phase is attributed to the solid-state phase transformation of austenite (γ → γ2 + σ). In the late stages of solidification, the concentration of chromium and Mo in the residual liquid phase increases, and due to insufficient diffusion, there are significant compositional differences between the interdendritic regions and the matrix. The enriched Cr and Mo cause the interdendritic austenite to become supersaturated, leading to solid-state phase transformation during subsequent cooling, thereby promoting σ phase precipitation. The overall phase transformation process can be summarized as L → L + γ → γ → γ + γ2 + σ. Y microalloying has a significant influence on the solidification process. The addition of Y increases the nucleation temperature of austenite, raises nucleation density, and refines the solidification microstructure. However, Y addition also leads to an increased amount of eutectoid structures. This is primarily because Y broadens the solidification temperature range of the alloy and prolongs grain growth perio, which aggravates the microsegregation of elements such as Cr and Mo. Moreover, Y raises the initial precipitation temperature of the σ phase and enhances atomic diffusion during solidification, further promoting σ phase precipitation during the subsequent eutectoid transformation.

Improving ductility via grain structure control in Sc/Zr modified Al-Cu-Li alloys by pulsed-laser powder bed fusion

ABSTRACT Sc/Zr modification significantly enhances the printability of high-strength Al-Cu-Li alloys, but poor ductility continues to limit the application of additive manufactured aluminum alloys as advanced component. Here, we proposed a point-by-point deposition strategy based on pulsed-laser powder bed fusion (PLPBF) to precisely control grain structures in Sc/Zr modified Al-Cu-Li alloys. This method successfully breaks the characteristic of melt pool under traditional continuous laser mode, making each ‘point’ melt pool has an independent solidification process. It facilitates the remelting of columnar grains within the melt pools while preserving the equiaxed grains at the edges. Leveraging the spatial distribution features, columnar grains are completely eliminated, resulting in a fully equiaxed grain structure in the printed sample. Meanwhile, the average grain size is reduced by 40%, accompanied by a slight increase in the volume fraction of Al3(Li,Sc,Zr) precipitates. The samples fabricated via pulsed laser exhibit a remarkable 211% improvement in elongation compared to those fabricated by continuous laser, with only a minor 7.6% decrease in tensile strength due to the shift from heterogeneous deformation induced (HDI) strengthening to grain refinement strengthening. This strategy enables tunable microstructural design in various alloy systems, offering enhanced flexibility to balance strength and ductility for advanced engineering applications.

Microstructure, Hardness and Tribological Characteristics of High-Entropy Coating Obtained by Detonation Spraying

In this study, powders based on a high-entropy AlCoCrFeNi alloy obtained by mechanical alloying were successfully applied to a 316L stainless steel substrate by detonation spraying under various conditions. Their microstructural features, phase composition, hardness, and wear resistance were studied. A comparative analysis between the initial powder and the coatings was performed, including phase transformation modeling using Thermo-Calc under non-equilibrium conditions. The results showed that the phase composition of the powder and coatings includes body-centered cubic lattice (BCC), its ordered modification (B2), and face-centered cubic lattice FCC phases, which is consistent with the predictions of the Scheil solidification model, describing the process of non-equilibrium solidification, assuming no diffusion in the solid phase and complete mixing in the liquid phase. Rapid solidification and high-speed impact deformation of the powder led to significant grain refinement in the detonation spraying coating, which ultimately improved the mechanical properties at the micro level. The data obtained demonstrate the high efficiency of the AlCoCrFeNi coating applied by detonation spraying and confirm its potential for use in conditions of increased wear and mechanical stress. AlCoCrFeNi coatings may be promising for use as structural materials in the future.

Composition Design of a Novel High-Temperature Titanium Alloy Based on Data Augmentation Machine Learning.

The application fields of high-temperature titanium alloys are mainly concentrated in the aerospace, defense and military industries, such as the high-temperature parts of rocket and aircraft engines, missile cases, tail rudders, etc., which can greatly reduce the weight of aircraft while resisting high temperatures. However, traditional high-temperature titanium alloys containing multiple types of elements (more than six) have a complex impact on the solidification, deformation, and phase transformation processes of the alloys, which greatly increases the difficulty of casting and deformation manufacturing of aerospace and military components. Therefore, developing low-component high-temperature titanium alloys suitable for hot processing and forming is urgent. This study used data augmentation (Gaussian noise) to expedite the development of a novel quinary high-temperature titanium alloy. Utilizing data augmentation, the generalization abilities of four machine learning models (XGBoost, RF, AdaBoost, Lasso) were effectively improved, with the XGBoost model demonstrating superior prediction accuracy (with an R2 value of 0.94, an RMSE of 53.31, and an MAE of 42.93 in the test set). Based on this model, a novel Ti-7.2Al-1.8Mo-2.0Nb-0.4Si (wt.%) alloy was designed and experimentally validated. The UTS of the alloy at 600 °C was 629 MPa, closely aligning with the value (649 MPa) predicted by the model, with an error of 3.2%. Compared to as-cast Ti1100 and Ti6242S alloy (both containing six elements), the novel quinary alloy has considerable high-temperature (600 °C) mechanical properties and fewer components. The microstructure analysis revealed that the designed alloy was an α+β type alloy, featuring a typical Widmanstätten structure. The fracture form of the alloy was a mixture of brittle and ductile fracture at both room and high temperatures.

Friction Stress Analysis of Slag Film in Mold of Medium-Carbon Special Steel Square Billet

Non-uniform friction and lubrication are the key factors affecting the surface quality of the casting billet. Based on the three-layer structure of the casting powder in the mold, the frictional stress in the mold was calculated and analyzed by using the relationship between the frictional stress and the thickness and viscosity of the liquid slag film, and the lubrication state between the cast billet and the mold was evaluated. Based on the actual production data of 40Mn2 steel and combined with the numerical simulation results of the solidification and shrinkage process of the molten steel in the mold by ANSYS 2022 R1 software, the frictional stress on the cast billet in the mold was calculated. It was found that within the range of 44~300 mm from the meniscus, the friction between the cast billet and the mold was mainly liquid friction, and the friction stress value increased from 0 to 145 KPa. Within 300–720 mm from the meniscus, the billet shell is in direct contact with the mold. The friction between the cast billet and the mold is mainly solid-state friction, and the friction stress value increases from 10.6 KPa to 26.6 KPa. It indicates that the excessive frictional stress inside the mold causes poor lubrication of the cast billet. By reducing the taper of the mold and optimizing the physical and chemical properties of the protective powder, within the range of 44~550 mm from the meniscus, the friction between the cast billet and the mold is mainly liquid friction, and the friction stress value varies within the range of 0–200 Pa. It reduces the frictional stress inside the mold, improves the lubrication between the billet shell and the mold, and completely solves the problem of mesh cracks on the surface of 40Mn2 steel cast billets.

An additively manufactured near-eutectic Al–Ce–Ni–Ti–Zr alloy: microstructure, mechanical properties and heat resistance

ABSTRACT Nowadays, heat resistance of additively manufactured aluminum alloys is highly in demand to meet the high-temperature strength requirements for lightweight components. However, existing commercially-available alloys exhibit severe strength degradation at elevated temperatures due to coarsening of strengthening phases. In this study, an additively manufactured near-eutectic Al–Ce–Ni–Ti–Zr alloy with superior heat resistance was developed based on the thermodynamic calculations. The new alloy possesses good printability thanks to the combination of the near-eutectic Al–Ce–Ni composition and inoculation treatment provided by Ti and Zr micro-additions. The eutectic solidification microstructure comprises a high volume of coarsening-resistant Al11Ce3 and Al3Ni phases and presents a typical hierarchical microstructure where refined equiaxed grains decorates melt boundaries. Such microstructure characteristics determine excellent heat resistance and good mechanical properties at ambient and elevated temperatures with 400°C. The alloy possesses a yield strength of 427 MPa and an elongation of 4.7% at ambient temperature. Even at 400°C, the alloy still retains a superb tensile yield strength of 104 MPa and an elongation of 17.86%. This work provides an effective pathway for heat-resistant aluminum alloy design via additive manufacturing and other rapid solidification processes.

Experimental Study on Slurry Ice Formation in Right Circular Cylinder and Its Empirical Model

Slurry ice has the potential to serve as a secondary working fluid for cooling purposes or as a cold storage medium due to its high energy intensity. In the latter application, it can overcome the drawbacks associated with using regular ice, such as ice bridging and insulation, thereby enhancing heat transfer between the exchanger surface and the surrounding medium. However, the solidification process depends on various factors, including the concentration of the freezing point depressant, the freezing point of the working medium, the size and shape of the storage medium, and its thermal properties. This study investigated the formation of slurry ice using water-ethanol and water-propylene glycol mixtures with different concentrations of freezing point depressants. The experiments were conducted in a freezer at temperatures around -15 and -20oC. The findings revealed that higher concentrations of freezing point depressants resulted in a faster growth rate of ice, however when the concentration exceeded 8 wt%, the opposite effect was observed. To better understand the process phenomena, a set of new empirical models was developed using polynomial curve fitting of related parameters in dimensionless forms to predict the amount of slurry ice formed over time. The results from the models showed good agreement with the experimental data across different concentrations of freezing point depressants and container sizes.

First-principles study of work functions and micro-galvanic corrosion between Mg and Mg–Dy intermetallics

Abstract The rare earth element Dy, as an alloying element, is applied in the preparation of binary magnesium alloys and has a positive impact on the corrosion resistance and mechanical properties of magnesium alloys. However, during the solidification process of Mg–Dy alloys, second phases with different electrochemical potentials from the magnesium matrix precipitate, significantly affecting the localized corrosion of the alloy. To reveal the causes of micro-galvanic corrosion in Mg–Dy alloys, this study, based on first-principles calculations using density functional theory, calculates the work functions of different crystal planes of four second phases (Mg1Dy1, Mg2Dy, Mg3Dy, and Mg24Dy5) in Mg–Dy alloys, and analyzes the results at the electronic level. Meanwhile, the focus was placed on comparing the work functions between the second phases and the matrix phase to determine their roles in micro-galvanic corrosion. The intrinsic potential differences between these four second phases and the magnesium matrix were determined. In addition, to verify the accuracy of the simulation results, Mg–Dy alloy samples—Sample 1 (mainly containing Mg3Dy) and Sample 2 (mainly containing Mg24Dy5)—were prepared, and electrochemical experiments were conducted. The calculation results indicate that the work function values of the different terminating planes of the four intermetallic phases (Mg1Dy1, Mg2Dy, Mg3Dy, and Mg24Dy5) in Mg–Dy binary alloys are all greater than the electronic work function of the magnesium matrix, suggesting that these phases act as the anodic phases in micro-galvanic corrosion and are preferentially corroded, thereby alleviating the corrosion rate of the matrix. The experimental results showed that, compared to Sample 1 (Mg3Dy), Sample 2 (Mg24Dy5) exhibited better corrosion resistance, which was consistent with the results obtained from computational analysis. This study also found that the work functions of different exposed surfaces of different crystal planes, as well as the same crystal planes, vary, and the corrosion behavior differs accordingly. The exposure of different surfaces has a significant impact on the intrinsic potential difference. These first-principles based electronic-level explanations provide insights into the micro-galvanic corrosion mechanisms of Mg–Dy alloys and offer theoretical guidance for the design and research of corrosion resistant magnesium based alloys.

Comparative Study on the Microstructure and Simulation of High-Speed and Conventional Fe-Based Laser-Cladding Coatings

High-speed and conventional laser cladding technologies were used to prepare Fe-based alloy cladding layers on the surface of 45 steel, compare and analyze the microstructure, microhardness, and phase structure of the two cladding layers, and study and analyze the morphology of the molten pool under the two cladding technologies, as well as the mechanism of evolution of the microstructure of the molten pool during the solidification process. The results show that, compared with the conventional laser melting coating, the grain size of the high-speed laser melting coating is finer, and the cooling rate at the top for conventional laser melting is 5.72 × 103 K/s, and the cooling rate for high-speed laser melting is 3.53 × 105 K/s. The microhardness of the high-speed laser melting coating has been significantly improved, and the solidification rates at the top for the two types of laser melting are the highest, namely 5.84 mm/s and 24.7 mm/s; the molten pool in conventional laser melting is usually larger and deeper, presenting a wide and deep shape, whereas the high-speed laser molten pool is usually shallower and narrower, with a flatter shape, presenting a comet trail, and the fast-cooling and fast-heating effects of high-speed laser melting are more significant.

A particle-based approach for the prediction of grain microstructures in solidification processes

A particle-based approach for the prediction of grain microstructures in solidification processes

Microstructure evolution upon directional solidification process of Nb-Si based ultrahigh temperature alloy

Microstructure evolution upon directional solidification process of Nb-Si based ultrahigh temperature alloy

Retraction notice to “Solidification process of hybrid nano-enhanced phase change material in a LHTESS with tree-like branching fin in the presence of thermal radiation” [J. Mol. Liq. 275 (2019) 10019

Retraction notice to “Solidification process of hybrid nano-enhanced phase change material in a LHTESS with tree-like branching fin in the presence of thermal radiation” [J. Mol. Liq. 275 (2019) 10019

The Effect of Forced Melt Flow by a Rotating Magnetic Field and Solid/Liquid Front Velocity on the Size and Morphology of Primary Si in a Hypereutectic Al-18 wt.% Si Alloy.

Hypereutectic Al-Si alloys containing primary Si exhibit unique material properties that make them suitable for various industrial applications. Understanding the characteristics of primary Si is crucial for predicting the effect of solidification conditions on the microstructure of these alloys. This paper presents a comprehensive characterisation study of primary Si in hypereutectic alloys. This study provides a detailed analysis of the size, distribution, and morphology of primary Si, providing valuable insights into the alloy structure, mechanical properties, and even the performance of the production process. The effect of forced melt flow by a rotating magnetic field (RMF) and solid/liquid front velocity on the size and morphology of primary Si in a hypereutectic Al-18 wt.% Si alloy was investigated. The purpose of using the RMF technique during the solidification process of Al-Si alloys is to enhance the alloy's microstructure by inducing electromagnetic stirring. The hypereutectic samples were solidified at five different front velocities (0.02, 0.04, 0.08, 0.2, and 0.4 mm/s), under an average temperature gradient (G) of 8 K/mm, in a crystalliser equipped with an RMF inductor. Each sample was divided into two parts: the first solidified without stirring, while the second underwent electromagnetic stirring using RMF at an induction (B) of 7.2 mT. The results revealed that increasing the front velocity during solidification refined the primary Si in stirred and non-stirred parts. In non-stirred parts, it decreased dendritic forms and increased star-like Si, while polyhedral shapes remained nearly constant. Stirred parts showed stable Si morphology across velocities. Higher velocities also promoted equiaxed over elongated Si forms in both parts.

Investigation of the Mechanism of Central Crack Formation During the Solidification and Reduction Process of GCr15 Bearing Steel

Investigation of the Mechanism of Central Crack Formation During the Solidification and Reduction Process of GCr15 Bearing Steel

Application of stabilized contaminated soils as metaconcrete aggregates

Abstract We present an initial study on the use of contaminated soils, effectively treated through a solidification and stabilization (S/S) process that renders them inert, as encapsulated aggregates in the creation of novel metaconcretes. Several mix designs of solidified and stabilized soils are carefully examined, and their physical and mechanical properties are characterized experimentally. These properties are crucial for determining how these treated soils can be effectively incorporated into metaconcretes, a class of materials known for their unique ability to attenuate mechanical waves through resonant structures. The frequency bandgap response of metaconcretes incorporating rubber-coated aggregates made from solidified soils is studied using analytical formulations. The results indicate that the proposed reutilization technique for contaminated soils not only ensures their safety but also offers significant potential for applications in the construction of blast-protective structures and seismic-shielding metamaterials.

Modeling two-ways fluid-solid phase transitions in lava using Smoothed Particle Hydrodynamics

Phase transitions are a key phenomenon in the evolution of lava flows, significantly influencing their emplacement and the formation of geological features such as lava channels and lava tubes. Here, a numerical model employing Smoothed Particle Hydrodynamics (SPH) to simulate two-way phase transitions between solid and fluid states in lava is presented. By accurately representing the solidification dynamics and incorporating a temperature range that accounts for the solidus and liquidus temperatures, the model addresses limitations in previous approaches that relied on oversimplified phase transition assumptions. We validate the model against Stefan’s benchmark test case and apply it to two illustrative volcanic scenarios using artificial volcanic-like environments, demonstrating how the model effectively captures the processes of solidification and fusion within the modeled lava flow. The results underscore the importance of phase transition modeling in understanding the complex behavior of lava flows in real-world volcanic contexts.

Coupled Temperature-Flow Field and Microstructure Numerical Simulation of the Solidification Process for Cu-3Ti-0.2Fe Alloy.

This work investigates the time-dependent changes in temperature, flow, and solidification microstructure under various cooling conditions. The mechanism of the effects of different pouring temperatures on the morphology and evolution of the solidification microstructure is explored. During gradual cooling, the temperature distribution remained consistent and the solid-liquid interface extended to its furthest extent. In contrast, water cooling generated the most pronounced temperature gradient at the solidification front, which was conducive to the development of columnar grains. Specifically, the maximum solidification rates at the center of the casting under the water-cooled copper mold, copper mold, and ceramic mold conditions were 2.71 mm/s, 1.45 mm/s, and 0.95 mm/s, respectively, with water cooling achieving the fastest rate. In the early stages of solidification, the flow velocity at the casting center was relatively high, and during slow cooling, the molten material tended to flow toward the surface. When air cooling was applied, the molten material at the center migrated outward, while under water cooling, the fluid moved in an upward direction. At a heat transfer coefficient of 100 W/(m2·K), the alloy primarily formed equiaxed grains; however, at 5000 W/(m2·K), the proportion of columnar grains increased significantly, and the average grain area expanded from 3.664 × 10-6 m2 to 4.441 × 10-6 m2. Additionally, as the pouring temperature increased from 1100 °C to 1200 °C, the number of grains decreased, while the average radius grew from 1.665 × 10-3 m to 1.820 × 10-3 m, resulting in a reduced fraction of equiaxed grains. This study provides valuable theoretical insights for optimizing the solidification process of this particular alloy.

Effect of Aluminum Content on Solidification Process and Microsegregation of δ-TRIP Steel

As a third-generation advanced high-strength steel (AHSS), δ-TRIP steel exhibits the characteristics of high strength, high plasticity, and low density. However, the addition of Al to steel will affect solidification and segregation, which may impact the final microstructure and mechanical properties of the product. In this study, thermodynamic calculations and microsegregation model analysis were employed to investigate the effects of Al addition on the solidification path, peritectic reaction range, equilibrium partition coefficients, and microsegregation behavior of δ-TRIP steel. The results show that with an increase in the Al content, the carbon content range in which δ ferrite is retained without complete transformation during the solid-state phase transition becomes broader. Simultaneously, the carbon concentration range of the peritectic zone expands. The segregation of the C, Si, Mn, P, and S elements increases with increasing Al content, whereas the segregation of Al decreases as the Al content increases. Under non-equilibrium solidification conditions, unlike equilibrium solidification, the temperature difference between the solid and liquid phases initially increases, then decreases, and subsequently levels off with further Al addition. This study provides information for the composition design and production process optimization of δ-TRIP steel, and the research results can provide a reference for similar high-aluminum, low-density steels.

Decoding the formation of barred olivine chondrules: Realization of numerical replication.

Millimeter-sized silicate spherules embedded in primitive meteorites, namely, "chondrules," are the primary solid component of the early solar nebula. They exhibit distinctive solidification textures, formed through rapid cooling from a molten state. The formation conditions of these textures have primarily been inferred on the basis of dynamic crystallization experiments; however, the theoretical verification of the solidification process has been largely neglected. Here, we conducted numerical simulations of the solidification of chondrule melt and successfully reproduced a crystal growth pattern resembling a typical barred olivine chondrule texture. This pattern emerged under conditions of rapid cooling, exceeding 104kelvins hour-1, which is substantially larger than those inferred experimentally. These results suggest that theories of chondrule formation in the nebula, which have been developed based on experimental results, should be reexamined.