Crystal Solidification Research Articles

DenMap single crystal solidification structure feature extraction: Automation and application

A fully automatic, standardised, and validated dendritic core detection algorithm, DenMap, is applied to analyse CMSX-4® and CMSX-10® single crystal microstructure. Through the utilisation of novel imaging techniques such as Gaussian deconvolution and minimisation-based thresholding, the newly enhanced version of DenMap demonstrates a significant improvement in detection accuracy and range of applications. The results indicate dendrites preferentially form channels, with array disorder increasing with height from the chill plate. A new twisting phenomenon has been observed that may have significant impact on the development of low and high angle grain boundaries and porosity formation within the microstructure. DenMap provides the foundation for 3D reconstruction methodologies and advanced pattern recognition techniques. This new standardised approach will facilitate the development of machine learning algorithms and eventually AI for single crystal solidification studies, particularly for the purpose of process optimisation.

Kinetics of geopolymer’s solidification: Effect of concentrations and curing temperatures

This paper report the experimental study on the kinetic of geopolymer’s solidification by determining setting time by varying activator concentrations of 10 M, 12 M, 14 M and 16 M, and curing temperatures of 30, 60, 80 and 100°C. However prior to the study of the effect the feasiblity of equipment using Vicat Needle. The transformation process of geopolymer crystal formation is analyzed by Avrami’s kinetica theory. From the results of the experimental showed the increase activator concentration and curing temperature produce shorter setiing time for geopolymer’s solidification. From the Avrami kinetic teory’s the growth form of crystal in the geopolymerization showed constant (K) of particle growth is 5.42 × 10-2 and the value of Avrami’s component n = 2.310 so that it can be concluded from the perspective of Avrami’s kinetic theory, the rate of crystal growth solidification in this geopolymerization process shows a two-dimensional structure.

Rapid crystallization of precious-metal-mineralized layers in mafic magmatic systems

The solidified remnants of mafic magmatic systems host the greatest concentrations of platinum-group metals in the Earth’s crust. Our understanding of precious-metal mineralization in these intrusive bodies is underpinned by a traditional view of magma chamber processes and crystal mush solidification. However, considerable uncertainty remains regarding the physical and temporal controls on concentrating these critical metals, despite their importance to modern society. We present high-precision 87Sr/86Sr analyses of plagioclase and clinopyroxene from within centimetre-thick precious-metal-enriched layers in the Palaeogene open-system Rum layered intrusion (northwest Scotland). Isotopic heterogeneity is present between plagioclase crystals, between clinopyroxene and plagioclase and within plagioclase crystals throughout the studied section. On the basis of these observations, we demonstrate that platinum-group element mineralization formed by repeated small-volume reactive melt percolation events. The preservation of strontium isotope heterogeneities at 10–100 µm length scales implies cooling of the melts that formed the precious-metal-rich layers occurred at rates greater than 1 °C per year, and cooling to diffusive closure within tens to hundreds of years. Our data highlight the importance of cyclic dissolution–recrystallization events within the crystal mush and raise the prospect that precious-metal-bearing mafic intrusions may form by repeated self-intrusion during cooling and solidification. Mineralization of platinum-group elements in mafic intrusions occurs due to repeated self-intrusion of magma, according to strontium isotope heterogeneities preserved in the Rum layered intrusion, Scotland.

The relationship between crystal morphology and solidification characteristics for VT3-1 alloy during vacuum arc remelting

We consider the crystallization morphology formation of VT3-1 (Ti-6.5Al-2.5Mo-1.5Cr-0.5Fe-0.3Si) titanium alloy during vacuum arc remelting (VAR). Combining a mathematical model and data acquired from radiograph experiments, unknown model parameters are determined. A refined mathematical model is compared to radiograph data with quite similar results. Using a ”tuned” model, important solidification characteristics, such as the temperature gradient G at the solidification front, and its velocity V are calculated. An industrial ingot remelting trajectory is presented in GV-space using a GV-map. The essential importance of the GV-map to the VAR process is demonstrated.

Multiphase-field and experimental study of solidification behavior in a nickel-based single crystal superalloy

Understanding the solidification behavior in nickel-based single crystal superalloy solidification is essential for determining the following heat treatment process, while the experimental findings have led to contradictory results. On the one hand, the fine γ/γ′ structure in the interdendritic zone suggests a eutectic reaction. On the other hand, the coarse γ′ precipitates indicate a peritectic reaction. In this work, the CALPHAD-based multiphase-field model was used to investigate the superalloy solidification behavior and complex γ/γ′ morphology generation. The fine γ/γ′ and coarse γ′ patterns were reproduced in the γ/γ′ colony, which were compared with the interdendritic microstructure observed by experiments. And the eutectic and peritectic reactions were verified by analyzing the chemical driving force at the phase interfaces. The simulation results suggest that the coarsening of γ′ in the γ/γ′ colony was due to the fast decrease of chemical driving force at the γ/l and γ'/l interfaces. Besides, remelting of the γ dendrite was found near the bulk γ′, which can be mainly ascribe to the increasing of Mo concentration rejected by the growing γ'. The simulated microsegregation patterns of the alloy components were also obtained and the results were in good agreement with the experimental findings.

Investigation of Start Block and Corresponding Influence for Grain Selection during Casting of Single-Crystal Superalloys.

To figure out the impact of the parameters of a starter block (the diameter D and height H) on grain selection and the selecting mechanism, a spiral selector was measured with optical microscopy (OM) and electron backscatter diffraction (EBSD) during the solidification of Ni-based single crystal (SX) superalloys. In this experiment, starter blocks with diameters of 8 mm, 10 mm, 15 mm, and 30 mm and a height of 30 mm were designed to find the best parameters. Recommendations for optimizing starter block geometry are provided.

The formation of Al6 (Fe, Mn) phase in die-cast Al-Mg alloys

In aluminium alloys, iron is a common impurity as it is unavoidably picked up in practice. The excessive Fe is strongly prone to form various intermetallic phases. These Fe-rich intermetallics are generally brittle and act as stress raisers to weaken the coherence with Al matrix, therefore decreasing elongation. However, Fe addition in Al-Mg alloys may be beneficial because of the improvement in the yield strength with the scarification of ductility of die-cast aluminium alloys. The morphology of intermetallic phases has a vital effect on the properties of aluminium alloys. In the present work, the 3D morphology of Al6 (Fe, Mn) in die-cast Al-Mg-Mn alloys with different levels of Fe contents were revealed. The formation of Al6 (Fe, Mn) was also studied through crystal features and solidification behaviours.

Preparation of Glass-ceramics Using Chromium-containing Stainless Steel Slag: Crystal Structure and Solidification of Heavy Metal Chromium

It is a useful way to stabilize the elements of heavy metal in the glass-ceramics with the form of ions due to the environmental pollution of heavy metal, such as Cr. The glass-ceramics of excellent combination properties were prepared, and the effect of stabilizing Cr-containing stainless steel slag with different concentrations of nitric acid leaching test were investigated. It was found that the major crystalline phase was diopside or anorthite with or without the amount stainless steel slag. Moreover, the continuous refinement of grains exhibited with the increase of amount of stainless steel slag. The results indicated that the excellent physical and mechanical properties, including density (2.9 g/cm3), hardness (729.27HV0.3), bending strength (222.9 MPa), and the solid solution of Cr in excess of 0.00057% for the glass-ceramics were related to the change of microstructure and phase structure. There showed the potential for reusing and detoxifying stainless steel slag.

Effects of molecular complexation on phase equilibria in mixtures of urea/polyethylene glycol derivatives and electrochemical performance of urethane based polymer electrolyte membranes for solid-state lithium ion battery

Phase diagram approach has been extended to the determination of phase diagram of a binary pair of urea with polyethylene glycol (PEG) in order to providence guidance to the formulation window of isotropic polymer electrolyte membranes (PEMs) with emphasis on the electrochemical performance. Effect of molecular weight of PEG on solid-liquid phase diagrams of its mixtures with urea has been demonstrated experimentally and theoretically. The observed change of eutectic, immiscibility loop, azeotrope type phase diagrams with increasing PEG molecular weight (or decreasing chain-ends) has been analyzed in the context of the combined Flory-Huggins (FH) theory of liquid-liquid demixing and phase field (PF) theory of crystal solidification. This rich phase behavior has been captured via the variation of crystalline-crystalline interaction strength of the combined FH-PF free energies. Subsequently, the phase diagram of poly (ethylene glycol) diacrylate (PEGDA)/urea was constructed in the framework of the aforementioned FH-PF theory. The incorporation of urea not only dissociates lithium cation from its salt, but also enhances the ionic conductivity of urea-modified polymer electrolytes dramatically. However, small molecule hydrophilic urea was found to be electrochemically unstable in the charge/discharge cycling test. To alleviate such shortcoming, urea (or urethane) linkage was imparted into the network chains by synthesizing PEG-bis(carbamate dimethacrylate) (PEGBCDMA) and subsequently photopolymerizing in the presence of SCN plasticizer and LiTFSI salt to afford the ion conductive PEM network. The as-synthesized PEGBCDMA based PEM consisting of PEGBCDMA/SCN/LiTFSI (20/40/40 ratio by weight) turned out to be completely amorphous and transparent before and after photo-crosslinking. The incorporation of urethane linkages in the PEM network exhibited enhanced ionic conductivity, improved thermal stability, and superior tensile properties with improved capacity retention during charge/discharge cycling, suggesting potentials for application in solid-state lithium ion battery.

High Resolution 3D Phase Field Simulations of Single Crystal and Polycrystalline Solidification

High Resolution 3D Phase Field Simulations of Single Crystal and Polycrystalline Solidification

Phase-field model for growth and dissolution of a stoichiometric compound in a binary liquid.

We propose a simple formulation of the phase-field model for a stoichiometric compound growing in a binary liquid. In previous models, chemical free energies of stoichiometric compounds have been approximated by parabolic functions of composition; however, the curvature has been determined arbitrarily in spite of the fact that the stoichiometric composition was undesirably modified depending on the curvature. To avoid this uncertainty, we supposed that the chemical free energy of the stoichiometric compound is represented by a single value at a given temperature and derived the phase-field equations without the parabolic free-energy approximation. The phase mobility was derived both for diffusion- and interface-controlled solidification based on a thin interface limit analysis. We carried out numerical simulations of one-dimensional calculations both in diffusion-controlled and interface-controlled cases and found that the growth velocities agreed with the analytic predictions. We also examined two-dimensional solidification of a circular crystal and confirmed that the equilibrium state was shifted, as suggested by the Gibbs-Thomson effect. This study is an important step for phase-field modeling that includes stoichiometric compounds with their accurate thermodynamic properties.

Pengaruh Variasi Temperatur Terhadap Kinetika Reaksi Solidifikasi Fly Ash Paving Blok Geopolimer

This paper reported about the investigated of fly ash solidification with geopolymer process that studied temperature variation on the rate of solidification using Vicat Nidle apparatus and leaching tests on the content of heavy metals Cu, Pb, Cr and Cd in paving blocks after solidification. The transformation process of geopolymer crystalline formation was analyzed by Avrami’s kinetics theory (Avrami’s kinetica theory). From the results of the study obtained the optimum temperature of 80 oC, the highest rate of crystal growth solidification (K) value of 0.0475 and the Avrami exponent value (n) of 2.310 in this geopolymerization process shows a two-dimensional structure. From the results of leaching levels of heavy metals Cu, Pb, Cr and Cd in fly ash paving blocks are very small degraded in water and still below the environmental threshold.

Trace Element Constraints on the Differentiation and Crystal Mush Solidification in the Skaergaard Intrusion, Greenland

New major and trace element analyses of plagioclase and clinopyroxene in gabbros from the Skaergaard intrusion are used to understand the mechanisms of crystallization in the main magma body and in the crystal mush. Crystal cores show a continuous chemostratigraphic evolution in the Layered Series, with compatible elements (e.g. Cr and Ni in clinopyroxene) being progressively depleted from the bottom up, whereas incompatible elements (e.g. Sr, Ba, REE in plagioclase and clinopyroxene) become progressively enriched. We performed numerical models and showed that these trends can be explained by a simple process of fractional crystallization, except for the upper 20% of the intrusion where plagioclase and clinopyroxene trace element compositions depart from fractional crystallization trends. At this stage of magma chamber solidification, fractional crystallization becomes less efficient and is replaced by a major proportion of in situ, equilibrium crystallization. Trace elements also show significant variations in interstitial overgrowths on plagioclase and clinopyroxene cumulus crystals. They result from crystallization of the interstitial liquid in the liquid + crystal mush. However, incompatible elements, and especially REE, show a degree of enrichment in plagioclase rims (> 20 ppm Ce) that strongly exceeds the highest concentrations observed in plagioclase cores (up to 4 ppm Ce) at the top of the Layered Series. Such a strong enrichment is difficult to reconcile with a simple process of fractional crystallization of the interstitial liquid in the crystal mush, but may be related to the development of silicate liquid immiscibility in the crystal mush or to delayed nucleation of apatite. After the crystallization of plagioclase and clinopyroxene overgrowths, diffusive re-equilibration during a period of 0.1-0.25 Myr significantly changed the original zoning profiles. Ce flux from clinopyroxene into the plagioclase lattice of adjacent crystals could also have contributed to the strong Ce enrichment observed in plagioclase rims.

Orientation determination and manipulation of single ice crystal via unidirectional solidification

The growth of ice crystal has been widely investigated by researchers from various fields, but efficient method that can meet the experimental requirements for identifying and reproducing the ice crystal with specific orientation is still lacking. In this paper, an ice crystal can be characterized with unique orientation information, where tilt angle of optical axis α, extinction angle β and the angle γ relative to preferred orientation 〈1120〉 in the basal plane (0001) and the direction of temperature gradient G are determined based on the properties of optic polarization of hexagonal ice in the directional solidification. An integrated criterion for determining the orientation of hexagonal ice is proposed by combining the crystal optics and solidification interface morphology. Precise manipulation of the orientation of single ice crystal is achieved by using a step-by-step method via a unidirectional platform combined with a polarized optical microscope. Three coordinate systems are established to achieve the manipulation of ice. They are the microscope coordinate system termed as “A-P-L”, where A, P and L refer to the directions of analyzer, polarizer and incident beam of the optical microscope, respectively, the specimen box coordinate system named “xyz”, and the crystallographic coordinate system described by the optical axis and 〈1120〉 in the basal plane (0001). Ice crystals are all confined in a series of glass specimen boxes filled with KCl solution (0.2 mol/L) and the growth sequence of the single ice crystal from one specimen box to another is specially designed to ensure the specific orientation relations among specimen boxes, and the orientation relations among the specimen boxes are adjusted according to the integrated criterion. Single ice crystals with three typical orientations (α3=90°, β3 a=0°; α3=90°, β3b=90°; α4=90°, β4 dose not exist, γ ≈ 33°) relative to the microscope coordinate A-P-L are obtained, and their morphological characteristics of S/L interface are observed in situ under different pulling velocities (10.3 μm/s, 13.4 μm/s and 100 μm/s, respectively). In this paper we successfully solve the problem of orientation determination and manipulation of ice orientation in the study of directional solidification of ice crystal, which may provide an effective experimental approach for investigating the theoretical problems concerning ice crystal growth.

Temperature evolution and grain defect formation during single crystal solidification of a blade cluster

In order to investigate the asymmetry of thermal conditions during directional solidification, the temperature evolution and correspondingly developed undercooling in a simplified single crystal blade cluster were numerically simulated. Simulation results demonstrate that the temperature distribution at the blade platforms is obviously asymmetrical. On the outside of the blade which directly faces the heating element, the liquidus (TL) isotherms progress relatively smoothly. On the inside of the blades facing the central rod, however, the TL-isotherms are in concave shape and the slope goes upwards to the platform extremities. The average undercooling extent ΔT and undercooling time Δt at the inside are much higher than those at the outside. It was then predicted that the inside platform extremities have significantly higher probabilities of stray grain formation compared to the outside ones. A corresponding experiment was carried out and the metallographic examination exhibited the same side- and height-dependence of stray grain formation in the blades as predicted. On the inside of the blades, all platforms are occupied by stray grains, while the platforms on the outside are nearly stray grain free. The simulation result agrees very well with the experimental observation.

Phase‐Field Modeling of Microstructural Evolution by Freeze‐Casting

Freeze‐casting has attracted great attention as a potential method for manufacturing bioinspired materials with excellent flexibility in microstructure control. The solidification of ice crystals in ceramic colloidal suspensions plays an important role during the dynamic process of freeze‐casting. During solidification, the formation of a microstructure results in a dendritic pattern within the ice‐template crystals, which determines the macroscopic properties of materials. In this paper, the authors propose a phase‐field model that describes the crystallization in an ice template and the evolution of particles during anisotropic solidification. Under the assumption that ceramic particles represent mass flow, namely a concentration field, the authors derive a sharp‐interface model and then transform the model into a continuous initial boundary value problem via the phase‐field method. The adaptive finite‐element technique and generalized single‐step single‐solve (GSSSS) time‐integration method are employed to reduce computational cost and reconstruct microstructure details. The numerical results are compared with experimental results, which demonstrate good agreement. Finally, a microstructural morphology map is constructed to demonstrate the effect of different concentration fields and input cooling rates. The authors observe that at particle concentrations ranging between 25 and 30% and cooling rate lower than −5° min−1 generates the optimal dendrite structure in freeze casting process.

Discussion on Modeling Capability for Macrosegregation

Abstract Macrosegregation originates from the solute partitioning at the liquid-solid interface and the relative motion between liquid and solid phases during solidification of metal alloys. A suitable macrosegregation model should incorporate solidification thermodynamics, crystal growth kinetics, multiphase computational fluid dynamics, and even thermal-structural mechanics. No current model includes all those phenomena, hence leading to assumptions having to be made. This paper discusses some modeling assumptions regarding the treatment of (1) diffusion kinetics of crystal growth, (2) crystal dendritic morphology and (3) solidification shrinkage. Theoretical analyses based on test calculations were made. We find that some previous models, which over-simplified some of the aspects mentioned above for the purpose of computational efficiency, can only be applied to study macrosegregation qualitatively. They lead to significant error estimations of macrosegregation. When the quantitative accuracy for macrosegregation is of primary importance, the multiphase-based models with an appropriate treatment of these aspects, despite the sophisticated computational requirements, are recommended.

Orientation Characteristics of Single Crystal Superalloys with Different Preparation Methods

Single crystal superalloys have been prepared separately by a grain selector and a seeding technique in a high temperature gradient directional solidification furnace. The orientation characteristics were measured by XRD. Results indicate that for the grain selector method, the crystal solidification begins at the cooling plate with random nucleation, and through mutual competitive growth at the starter block. The grains enter the spiral selector, and finally the single crystal superalloys which are close to <001> direction are obtained. By the seeding technique, by epitaxial growth of partially melted seed crystals, single crystal superalloys which have the same orientation as the seed crystal are obtained.

Simulation of stray grain formation in Ni-base single crystal turbine blades fabricated by HRS and LMC techniques

The simulation models of the thermal and macrostructural evolutions during directional solidification of Ni-base single crystal (SX) turbine blades under high rate solidification (HRS) and liquid metal cooling (LMC) have been constructed using ProCAST software, coupled with a 3D Cellular Automaton Finite Element (CAFE) model. The models were used to investigate the tendencies of stray grain (SG) formation in the platform region of turbine blades fabricated by HRS and LMC techniques. The results reveal that the LMC technique can prohibit SG formation by smoothing the concaved isotherm and in turn alleviating the undercooling in the platform ends to let the dendrites fill up the undercooled zone before SG nucleation. The simulation results agreed well with the experimental results, indicating that these models could be used to analyze the macrostructural evolution or to optimize process parameters to suppress SG formation. Using these models, the critical withdrawal rate for casting SX turbine blades without SG formation were determined to be around 75 μm·s-1 and 100 μm·s-1 for HRS and LMC respectively, suggesting that LMC can be used as an efficient technique in fabricating SX turbine blades without any SG defect formation.

Role of molecular complexation in solid-liquid phase diagram of poly-ethylene oxide/urea mixture

Thermodynamic phase diagram of polyethylene oxide (PEO)/urea blend has been investigated with emphasis on the formation of induced crystals driven by molecular complexation. Of particular interest is that the complexed α crystal is more stable than those of neat constituents. The experimental solid-liquid phase diagram of PEO/urea blends has been analyzed in the context of the combined Flory-Huggins free energy for liquid-liquid demixing and phase field free energy of crystal solidification. The self-consistently calculated coexistence lines of the PEO/urea mixture exhibit an azeotrope type, accompanied by eutectoid reactions in the submerged regions, wherein the complexed α crystal decomposes into two coexistence crystalline phases. These coexistence crystalline phases were further analyzed by means of polarized optical microscopy, Fourier transform infrared spectroscopy, and wide-angle x-ray diffraction. A possible phase diagram of the complexed PEO/urea is constructed and discussed.