Eutectic Patterns Research Articles

Influence of FeS2 and FeSi75 in Double-Chamber Sample Cup on Thermal Analysis Curve and Graphite Morphology of Molten Iron

In the production of vermicular graphite cast iron, the allowable range of residual magnesium content in molten iron after treatment is very narrow, amounting to only 0.008%. Therefore, thermal analysis technology was used to quickly evaluate the vermiculation and inoculation level of molten iron at the furnace itself, thus allowing the molten iron to be adjusted in time. The additives in the sample cups play a crucial role in obtaining cooling curves with remarkable characteristics. In this study, either FeS2 or FeSi75 additives were added to one chamber of a double-chamber sample cup made of resin sand, in which the cavities of the double chambers were spherical with diameters of 30 mm. The thermal analysis curves of molten iron in the double-chamber sample cup were acquired using a double channel temperature recorder, and the solidified spherical samples were analyzed quantitatively. The influence of FeS2 or FeSi75 additives on both the cooling curves of molten iron and the graphite morphology were investigated. The experiment’s results indicated that when 0.05% FeS2 is added to one chamber of the sample cup, the cooling curve changes to the solidification pattern of gray cast iron. The continuous increase in the FeS2 additive has little influence on the shape of cooling curves, and the graphite changes form from vermicular to flaked. When the amount of FeS2 is increased from 0.05% to 0.10%, the resulting graphite changes from D-type and E-type to A-type and B-type. When the amount of FeS2 reaches 0.20%, the morphology of graphite is short and thick. With the increase in the amount of FeSi75 additive, the amount of spherical graphite in the sample cup increases gradually, and the vermicularity decreases gradually from 89% to 46%. With the increase in FeSi75 additive from 0 to 0.45%, we observed that the average diameter of graphite decreases from 23 μm to 19 μm and then increases to 22 μm. The eutectic recalescence temperature shows a decreasing trend, and the cooling curve gradually changes from a hypoeutectic to a eutectic pattern. The addition of 0.05% FeS2 or 0.45% FeSi75 to one chamber is more appropriate for a double-chamber sample cup with two spherical cavities with diameters of 30 mm. This lays a foundation for the optimization of additives when using the double-chamber sample cup for thermal analysis of vermicular graphite cast iron.

Gabriel Faivre: his legacy on eutectic solidification

In the honor of Gabriel Faivre (1944-2020), I will present a review of major scientific contributions to the understanding of the dynamics of eutectic growth patterns. From the end of the 1980s, Gabriel Faivre undertook a systematic research in solidification guided by the new concepts of the nonlinear physics of out-of-equilibrium pattern formation. Drawing on his outstanding capabilities as an experimentalist, he refined the method of in situ directional solidification of model alloys. With constant reference to physics and metallurgy, he succeeded in carrying out a high-level research, keen to reach strong qualitative impact and quantitative accuracy. Gabriel Faivre made key discoveries, together with coworkers and young researchers in Paris, and in collaboration with materials scientists and physicists in France and abroad. From symmetry breaking instabilities to eutectic cells and dendrites, over rod-like and labyrinth patterns, full light has been shed onto new phenomena, fascinating to the eye and the mind. During the last decade, Gabriel Faivre mentored an in-depth analysis of interfacial-anisotropy effects on coupled-growth patterns, thus reconciliating the theories of regular eutectics and crystal-orientation dependent eutectic-grain growth. Being both a rigorous scientist and a generous colleague, he left us a vast legacy of prospective research topics in solidification and crystal-growth science. Sharing his knowledge of fine arts and humanities, Gabriel Faivre also instilled the best of intellectual thinking in those who were fortunate enough to work with him.

Short-range ordering heredity in eutectic high entropy alloys: A new model based on pseudo-ternary eutectics

Eutectic high entropy alloys (EHEAs) have garnered wide attention in the metal community due to their excellent castability and unique microstructures. However, the formation mechanisms of these eutectic microstructures and their compositional design remain puzzling. In this paper, we have developed a simple yet unified pseudo-ternary model to unravel the puzzle of multiple eutectics in Ni-Al-containing high entropy alloys (HEAs) deploying a combination of the chemical similarity/dissimilarity coefficient concept, CALPHAD technique and first principle molecular dynamics simulation. Using the chemical similarity/dissimilarity parameters derived from CALPHAD model parameters and the eutectic valleys of Ni-Al-Cr, we reproduce the multiple eutectic patterns in the Ni-Al-containing HEAs and present a general approach for pinpointing the composition of eutectic HEA (EHEA) in the vast temperature-composition space. Aided by the first principle molecular dynamics calculation, we have shown that although the eutectic structures of Ni-Al containing EHEAs are different, the formation mechanism of the eutectic structure is similar, which stems from the short-range-ordering (SRO) heredity of EHEA liquid from the eutectic valleys of the pseudo Ni-Al-Cr ternary. Two EHEAs, EHEA 1 (Al16.95Cr16.95Fe19.1Ni47) with L12+B2 eutectic structures and EHEA 2 (Al33.5Cr33Co4Ni29.5) with BCC+B2 eutectic structures were designed using the model and experimentally verified. This unified Ni-Al-Cr ternary model, validated by experimental data in both literature and our fabricated EHEAs, presents a compelling solution to the long-debated grouping strategy in EHEA design and offers a new paradigm to map the complicated but intriguing eutectic microstructures in EHEAs and conventional alloys.

An interface-oriented data-driven scheme applying into eutectic patterns evolution

Solid-liquid interface dynamics plays a crucial role in microstructure evolution during solidification. However, it is difficult to extract sufficient spatial information to describe the variation in the irregular and non-periodic solid-liquid interface domains, resulting in a challenge remaining in quantifying analysis by a quick and low-dimensionally visualized way. We proposed an interface-oriented two-point statistics method to solve the unbiassed statistics of the spatial information in these irregular and non-periodic interfaces. The challenge was successfully overcome by a carefully designed data-driven scheme, which has the advantages of easy to operate, high accuracy and efficiency. Taking the eutectic microstructure evolution simulated by phase-field method as an example, we also obtained novel insights on tailoring eutectic patterns, that is, the transformation of four patterns (lamellar elimination, regular lamellae, oscillatory eutectics and branching lamellae) depends on initial lamella spacing whether the interface energy is isotropic or anisotropic. Additionally, interfacial energy anisotropy, compared to the isotropic case, not only prolongs the time of patterns transformation, but also narrows the spacing range between elimination and creation of lamellae. Our proposed scheme is also able to be applied into more occasions about microstructure evolution in different materials systems.

Grain size, carbide distribution and hardness issues pertaining to cutting tools produced from high speed steel scraps

ABSTRACT Single point cutting tool blanks are prepared adopting the centrifugal casting method using only scrapped high-speed steel tools collected from different installations for better mechanical properties and economical production. The cast cylindrical blanks are cut into shapes by wire-cut EDM and subsequently heat-treated. Upon heat treatment, the centrifugal cast tool exhibited a reduction of grain size about 60% accompanied by about 22.7% increase in the hardness. The conventional cast HSS M2 tools procured from the market are compared with centrifugal cast tools. SEM images of both tools showed two different eutectic carbide patterns. Also, the precipitation of M6C and MC carbides are found in XRD analysis for both tools. Upon EDX analysis, W, V, and Cr are found to be the prime elements responsible for carbide formation. Wear characteristics of centrifugal cast tool observed are as par with the HSS M2 tool during turning of mild steel (ASTM A36) under identical environment. This method will be helpful for the development of cutting tools for industrial applications.

Numerical investigation of eutectic growth dynamics under convection by 3D phase-field method

Control of eutectic growth trajectory is a technologically important subject in metallurgy and applied physics. The interaction between solute transport and interface capillary determines eutectic growth under convection. By employing a multiphase-field lattice-Boltzmann method, together with a parallel-adaptive mesh refinement algorithm, the effect of convection on 3D eutectic growth is quantified including lamellar and rod eutectics. The flow-induced solute distribution changes eutectic growth dynamics by establishing a new solute transport equilibrium. The growth behaviors of different eutectic patterns are investigated, and the eutectic growth dynamics is largely dependent on the constitutional undercooling and the curvature undercooling ahead of the solidification front. The natural convection changes the width ratio of coexisting solid phases, while the forced convection causes a tilt band for both lamellar and rod eutectics. Rod-to-lamellar transition under larger convection intensity, which is first predicted by numerical techniques, is discussed and good agreement with previous works is achieved. The deep understanding of the convection effect can help guide how to regulate eutectic patterns through changing the solidification condition.

Rod eutectic growth in bulk undercooled melts

This article proposes an analytical model to understand the rod growth of eutectic in the bulk undercooled melt. Based on the previous derivations of the lamellar eutectic growth models, relaxing the assumptions of small Péclet numbers, the model is derived by considering melt kinetic and thermal undercoolings. The intent of this model is to predict the transitions in eutectic pattern for conditions of the low and high growth velocities. In addition to investigation of the transition between lamellar and rod eutectic patterns, mathematical simplifications of solving Bessel function are presented as well, which is the most important priority to model calculation.

Coexistence of rod-like and lamellar eutectic growth patterns

We present the first observations of a large-scale coexistence between rod-like and lamellar eutectic growth patterns during directional solidification of a eutectic alloy. In situ experiments with real-time optical monitoring were carried out under microgravity onboard the International Space Station (ISS). We used the transparent succinonitrile-d,camphor eutectic alloy that ordinarily forms rod-like patterns. At low growth velocity, short lamellae stabilized at the contact line with a sample glass wall. In the presence of a controlled transverse temperature gradient, the coupled-growth pattern experienced a global drift along an inclined isotherm, and a stable lamellar domain spread over the solidification front. The propagative nature of the lamellar-to-rod transition was evidenced. The advance of the lamellar/rod domain boundary was determined by a slowly amplifying varicose instability of the lamellae. On a large scale, the domain boundary underwent a dynamic faceting.

Microstructural evolution in directionally solidified Al-Cu-Mg ternary eutectic

This work seeks to increase our fundamental understanding of microstructure evolution and pattern formation in multi-component, multi-phase metallic materials during freezing. The solidification behavior of three-phase Al-Cu-Mg eutectic was investigated via directional solidification using a Bridgman furnace with varied thermal gradients (G = 3.0–14.4 K/mm) and velocities (0.625–4.0 µm/s). Precise quantification of the resulting microstructures was carried out using phase fraction, eutectic spacing, axis ratio, phase size, and nearest neighbor measurements. The results of the qualitative and quantitative assessments of the evolving structure showed that the modified two-lamellar, one-rod microstructure previously presented for this system breaks down below a critical velocity. The effect of velocity, gradient and composition on the stability of the three-phase coupled growth is considered, and results are compared to thermodynamically predicted values. Unlike in the related eutectic system of Al-Ag-Cu, thermal gradient was found to have no measurable effect on either eutectic spacing or pattern, results which were further supported with inferential statistical tests (ANOVA and Tukey’s HSD).

A synergy of different corrosion failure modes pertaining to T91 steel impacted by extreme lead–bismuth eutectic flow pattern

This paper reports an attempt to speculate about corrosion resistance of T91 steel to extreme lead–bismuth eutectic (LBE) flow pattern. We build a modified dynamic corrosion apparatus permitting assemblages of oxidation, erosion or dissolution attack proceeding together within oxygen-saturated LBE. After corrosion test at 400℃ up to 1000 h, discrepancies of corrosion performance under various flow patterns were described by diffusion or mass transfer kinetics as well as erosion mechanics. In justification of dense Fe-O layer and cracks across oxide scales detected within typical erosion cavities, we put forward oxide growth stress enhanced by high surface curvature.

In-situ observation of eutectic growth during directional solidification of succinonitrile - (D)camphor- neopentyl glycol alloys under imposed velocity transients

In the present work are reported ground-reference results from a series of transient solidification experiments with the organic eutectic alloys SCN-23.6 DC (wt.%) and SCN-24.2DC-0.5NPG (wt.%), which have been performed in preparation of microgravity experiments using a new multi-user facility called Transparent Alloys or DIRSOL. In 1g lab conditions we investigated the response of rod-like eutectic patterns to imposed transients, involving defined acceleration and deceleration of the growth velocity. The patterns have been recorded in-situ in oblique view using a long distance optics and were analysed for a region of interest of 640 μm x 320 μm over long periods of time. The time dependent growth velocity and the associated acceleration / deceleration were determined using images from a side-view camera.The reported results mainly refer to the spacing distribution and the hexagonal order parameter S0, dynamically attained at a defined time instant, i.e. at the moment when the local growth velocity reaches V = 40 nm s−1 along deceleration 80 → 10 nm s−1 or acceleration 10 → 80 nm s−1 paths. The major result is that the hexagonal order is deteriorating under transient growth conditions compared to steady state conditions. We could not observe an increase of order for either imposed acceleration or deceleration, mainly because spacing adjustment is accomplished by abrupt morphological transitions which destroy the previous order.The abrupt morphological transitions are clearly identified as sharp events along an experiment cycle 80 → 10 → 80 nm s−1 and could conveniently be seen in hysteresis loop diagrams. Upon deceleration the abrupt spacing adjustment event corresponds to a transition from fibrous to vermicular morphology. Upon acceleration the abrupt spacing adjustment event corresponds to spontaneous rod splitting.

Phase boundary anisotropy and its effects on the maze-to-lamellar transition in a directionally solidified Al[sbnd]Al2Cu eutectic

Solid-solid phase boundary anisotropy is a key factor controlling the selection and evolution of non-faceted eutectic patterns during directional solidification. This is most remarkably observed during the so-called maze-to-lamellar transition. By using serial sectioning, we followed the spatio-temporal evolution of a maze pattern over long times in a large AlAl2Cu eutectic grain with known crystal orientation of the Al and Al2Cu phases, hence known crystal orientation relationship (OR). The corresponding phase boundary energy anisotropy (γ-plot) was also known, as being previously estimated from molecular-dynamics computations. The experimental observations reveal the time-scale of the maze-to-lamellar transition and shed light on the processes involved in the gradual alignment of the phase boundaries to one distinct energy minimum which nearly corresponds to one distinct plane from the family {120}Al||{110}Al2Cu. This particular plane is selected due to a crystallographic bias induced by a small disorientation of the crystals relative to the perfect OR. The symmetry of the OR is thus slightly broken, which promotes lamellar alignment. Finally, the maze-to-lamellar transition leaves behind a network of fault lines inherited from the phase boundary alignment process. In the maze pattern, the fault lines align along the corners of the Wulff shape, thus allowing us to propose a link between the pattern defects and missing orientations in the Wulff shape.

Effect of Destabilisation Period and Post Destabilisation Cooling Rate on the Evolution of Microstructure in 8.0 wt% Chromium White Cast Iron

To study the effect of destabilisation period and post-destabilisation cooling rate on the as-cast microstructure, continuous annealing involving prolonged austenitisation for 4 h followed by furnace cooling and cyclic annealing using repeated austenitisation, each of 0.66 h duration, followed by forced-air cooling were carried out at 900, 950, 1000, 1050 and 1100 °C on a 8.0 wt% chromium white iron. Destabilised microstructures show precipitation of secondary carbides on a pearlite plus martensite matrix after continuous annealing treatment and on a martensite plus austenite matrix after cyclic annealing treatment. Both the treatments exhibit characteristic role in monitoring the size and distribution of the secondary carbides and also in modifying the eutectic pattern with varying annealing temperature. At higher temperatures of 1050 and 1100 °C, absence of the secondary carbides becomes a common feature for both the heat treatments; while fragmentation of the eutectic carbides happens to be an additional feature after cyclic annealing of the as-cast alloy.

Quasi-isotropic and locked grain growth dynamics in a three-phase eutectic system

The anisotropy of the interphase boundaries has a substantial impact on the eutectic pattern formation. Using rotating directional solidification (RDS) technique, two distinct eutectic grains, namely quasi-isotropic (floating) and crystallographically-locked grains, were identified in three-phase In-Bi-Sn alloy system. The growth dynamics of these grains were investigated in thin samples. The ABAC-type growth pattern, where A, B, C are eutectic phases, is preserved in the quasi-isotropic grains upon evolution of the pattern over the entire crystallographic orientations in RDS experiments. In the locked grains, however, the regularity of the ABAC pattern is disturbed due to the existence of two-fold singularities, i.e. cusps over a well-defined angular range at the surface energy plot. Nevertheless, the ABAC pattern is recovered after the sequence of the unlocked/transient/locked/transient states. The characteristics of both grains are analogous to the nearly steady-state pattern formed upon standard directional solidification experiments. The quasi-isotropic and locked grains in a three-phase ternary eutectic system essentially have the similar dynamical features as the two-phase binary eutectic systems although the microstructural details are highly complex in the three-phase system. These similarities designate that the formation of quasi-isotropic and locked patterns is merely due to the inherent characteristics of the eutectic grains.

Eutectic pattern transition under different temperature gradients: A phase field study coupled with the parallel adaptive-mesh-refinement algorithm

Eutectic pattern transition under an externally imposed temperature gradient was studied using the phase field method coupled with a novel parallel adaptive-mesh-refinement (Para-AMR) algorithm. Numerical tests revealed that the Para-AMR algorithm could improve the computational efficiency by two orders of magnitude and thus made it possible to perform large-scale simulations without any compromising accuracy. Results showed that the direction of the temperature gradient played a crucial role in determining the eutectic patterns during solidification, which agreed well with experimental observations. In particular, the presence of the transverse temperature gradient could tilt the eutectic patterns, and in 3D simulations, the eutectic microstructure would alter from lamellar to rod-like and/or from rod-like to dumbbell-shaped. Furthermore, under a radial temperature gradient, the eutectic would evolve from a dumbbell-shaped or clover-shaped pattern to an isolated rod-like pattern.

Phase-field modeling of eutectic structures on the nanoscale: the effect of anisotropy

A simple phase-field model is used to address anisotropic eutectic freezing on the nanoscale in two (2D) and three dimensions (3D). Comparing parameter-free simulations with experiments, it is demonstrated that the employed model can be made quantitative for Ag–Cu. Next, we explore the effect of material properties and the conditions of freezing on the eutectic pattern. We find that the anisotropies of kinetic coefficient and the interfacial free energies (solid–liquid and solid–solid), the crystal misorientation relative to pulling, the lateral temperature gradient play essential roles in determining the eutectic pattern. Finally, we explore eutectic morphologies, which form when one of the solid phases are faceted, and investigate cases, in which the kinetic anisotropy for the two solid phases is drastically different.

Eutectic solidification patterns: Interest of microgravity environment

The solidification of binary eutectic alloys produces two-phase composite materials in which the microstructure, that is, the geometrical distribution of the two solid phases, results from complex pattern-formation processes at the moving solid–liquid interface. Since the volume fraction of the two solids depends on the local composition, solidification dynamics can be strongly influenced by thermosolutal convection in the liquid. In this contribution, we review our experimental and numerical work devoted to the understanding of eutectic solidification under purely diffusive conditions, which will soon be tested and extended during the microgravity experiment TRANSPARENT ALLOYS planned by the European Space Agency (ESA).

Composition, Microstructure, Phase Constitution and Fundamental Physicochemical Properties of Low-Melting-Point Multi-Component Eutectic Alloys

Low-melting-point alloys have an extensive applications in the fields of materials processing, phase change energy storage, electronic and electrical automatic control, continuous casting simulation, welding, etc. Specifically, the eutectic compositions make up a large number of low-melting-point alloys that are exploited because of their desirable features like single melting peaks, excellent operational reliability, and casting fluidity. However, the fundamental physicochemical properties from the current available literature on low-melting-point multi-component eutectic alloys (LMP-MCEAs) are rather rare and lowly accurate, including the exact melting temperatures and compositions, constituent phases, microstructures and morphologies, melting enthalpies, specific heats, densities, and so on. This lack of information seriously limits the development and application of low-melting-point multi-component eutectic alloys. In this paper, the low-melting-point multi-component eutectic alloys composed of Bi, Cd, Sn, Pb, and In elements synthesized by high vacuum induction melting and fundamental data were investigated by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and density analysis instrument. Most of the LMP-MCEAs with complex eutectic morphology structures and XRD diffraction patterns could be explained with the fact that they were three-phase eutectic alloys with mixed growth way. Generally, LMP-MCEAs present an extremely low melting point between 48.3 and 124 °C and high density between 8 and 10 g/cm3.

In situ observation of solidification patterns in diffusive conditions

We present a review of recent in situ experimentation studies of solidification front patterns and microstructures in alloys. Front-tracking diagnostics and real-time observation methods using high-resolution optical or X-ray imaging devices currently apply to model transparent systems as well as metallic alloys in thin and bulk samples. On a theoretical basis that spans the physics of nonequilibrium pattern formation and materials science, in combination with time-resolved numerical simulations, conclusive results of both fundamental- and applied-science interest have been obtained on major problems relative to multiscale microstructure selection, morphological transitions, and crystallographic effects during single- and multi-phase solidification. We will mainly focus on the dynamics of cellular, dendritic, and eutectic growth patterns in diffusive-growth conditions, that is, in the absence of convection in the liquid. This can be achieved in (semi-)thin samples, or, for bulk solidification, in the reduced-gravity environment of orbiting facilities. A selection of emerging work on, e.g., faceted growth and adaptive control of solidification patterns will furthermore be reported. We conclude by pointing out open questions and new perspectives for future research.

Microstructure transformation from irregular eutectic to complex regular eutectic in directionally solidified Al2O3/GdAlO3/ZrO2 ceramics by laser floating zone melting

Directionally solidified Al2O3/GdAlO3(GAP)/ZrO2(GdSZ) ternary eutectic ceramics have been grown by laser floating zone melting. The microstructure evolution rule is investigated as a function of growth rate. The as-solidified samples present high density (>99%), smooth surface and high diameter stability free of pores and cracks. Increasing the growth rate from 4 to 100μm/s, the microstructures undergo a transformation from “Chinese script” irregular eutectic pattern to eutectic colony and to complex regular eutectic patterns (lamellae or rods). The average interphase spacing of the “Chinese script” microstructure presents an inverse square relationship according to λ=10.46×ν−1/2, where the average interphase spacing λ has the dimension of μm and growth rate ν is in μm/s. While the interphase spacing of the complex regular microstructure is finer. The mechanisms of the microstructure evolution and the effects of ZrO2 phase on the morphology and domain size of microstructure are discussed in detail.